The immediate social environment dynamically shapes movement and foraging in wild Sumatran Orangutans (Pongo abelii)

The immediate social environment dynamically shapes movement and foraging in wild Sumatran Orangutans (Pongo abelii) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The immediate social environment dynamically shapes movement and foraging in wild Sumatran Orangutans (Pongo abelii) Emma Lokuciejewski, Margaret Crofoot, Maria van Noordwijk, Odd Jacobson, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9574845/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Background Social associations have well-established costs and benefits, and likely play a fundamental role in shaping animals’ movement. Individuals are predicted to balance the benefits of associating, including social learning and mating opportunities, against key costs such as feeding competition, resulting in context-dependent movement patterns. However, the effects of the immediate social environment on movement remain poorly understood, likely because most movement ecology research focusses on either strictly group living or solitary species. We investigate how social associations shape fine-scale movement patterns and food resource exploitation in wild, semi-solitary Sumatran orangutans ( Pongo abelii ) who show fission-fusion social dynamics. We integrated 16 years of spatial data on 72 individuals with detailed behavioural observations. We predicted that associations shape movement in ways that reflect distinct benefits and costs across age-sex classes. Methods We quantified the effects of associations on daily path length (a proxy for energetic investment in movement) using continuous-time movement models, path sinuosity (as a measure of movement efficiency), and the use of key food hotspots (as an indicator of feeding competition and spatial knowledge). Using linear mixed models, we tested how these metrics varied with time spent in association and age-sex class, controlling for ecological factors. Results Across all age-sex classes, daily path length increased with time in association, driven by longer active periods. At the population level, there was a trend towards straighter paths when individuals were with associates, though this depended on the class of the focal and the associate. Foraging behaviour was socially-sensitive, with all age-sex classes visiting fewer feeding hotspots when in associations, and spending less time feeding within them. Social influences on movement and foraging were most apparent in mothers, although flanged males also exhibited significant effects, including the greatest reduction in overall feeding time when in the presence of unflanged males compared to when alone. Conclusions Together, these results suggest that social associations entail costs and benefits for orangutans that are tangibly reflected in their movement and foraging decisions. Furthermore, different age-sex classes showed distinct adjustments in movement depending on who they associated with, highlighting the dynamic nature of social influences on behaviour. Foraging behaviour spatial ecology movement patterns daily path length sinuosity fission-fusion dynamics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 BACKGROUND Animal movement is shaped by an interplay of social and ecological factors, as well as individual- and group-level characteristics [ 1 , 2 ]. Movement ecology seeks to understand how these interacting factors generate patterns of movement across space and time that represent evolved adaptive responses [ 3 ]. Among these factors, sociality plays a central role: at the species level, it can facilitate or constrain individuals’ spatial decisions, while within species the immediate social environment (e.g., the duration and composition of social associations) may both drive movement and emerge as a consequence of individuals’ movement trajectories as they balance experienced costs and benefits [ 4 ]. The reciprocal relationship between the immediate social environment and movement remains poorly understood, largely owing to the complexities of social contexts that may influence individuals differently. Moreover, most movement ecology research has focused on species that are either strictly group-living or strictly solitary. Orangutans represent a particularly informative system for disentangling the interplay between the immediate social environment and movement because of their flexible and context dependent sociality. Orangutans are unique among great apes in exhibiting characteristically low and dynamic tendencies to associate with conspecifics, typically described as a semi-solitary fission-fusion dynamic [ 5 – 7 ]. This social system has been attributed to a combination of high energetic needs and predominantly frugivorous diet [ 8 ], which together impose a high caloric need in a habitat characterised by temporally fluctuating and spatially patchy food resources [ 9 ]. Despite being less gregarious than African great apes [ 10 , 11 ], orangutans do nonetheless associate more frequently than expected by chance [ 7 , 10 , 12 , 13 ], suggesting that social factors play a meaningful role in shaping their spatial ecology. Orangutan associations may be passive in nature with no direct social interactions, commonly observed at foraging sites [ 12 ], or active involving coordinated movement and social attraction [ 12 , 14 ]. They vary in size (i.e., the number of individuals involved) and composition (i.e., the identities of those individuals) and range from brief encounters lasting only minutes, to stable associations persisting over multiple consecutive days [ 5 , 13 , 15 ]. Association frequencies and sizes systematically vary across populations [ 7 , 10 ], age-sex classes [ 5 , 16 ], reproductive state [ 17 ], and habitat productivity [ 10 , 18 ], likely reflecting a dynamic balance between ecological and social costs and benefits. Orangutans are subject to pronounced energetic constraints arising from the combination of their relatively large brains, large body size, energetically costly arboreal locomotion [ 19 ], and reside in low-food-density habitats that limit energy acquisition. Together, these factors place individuals under persistent energetic pressure, requiring careful trade-offs in how energy is allocated, particularly with respect to movement. Given that locomotion in orangutans is already energetically demanding, deviations from energetically efficient movement due to the presence of conspecifics likely generates costs [ 15 , 20 ] that must be offset by social benefits [ 21 ]. Within this context, associations can provide important social benefits, such as facilitating mating [ 22 ], enabling social learning [ 23 , 24 ], and providing play opportunities for immatures [ 25 ]. However, associations can also impose costs, such as increased feeding competition [ 26 ], forced copulations [ 17 ], and potential infanticide risks [ 17 ]. Previous studies further suggest that association size increases an orangutan’s travel distance [ 5 , 15 , 27 ], though these studies acknowledge that individuals may differ in their intrinsic costs, such as direct locomotor costs and nutritional needs [ 5 ]. Conversely, avoiding associations with conspecifics may alleviate costs, though also reduce beneficial opportunities. All in all, the infrequency and conditional nature of orangutan associations and social interactions seem to reflect a trade-off between ecological constraints, energetic expenditure, and the potential advantages of sociality. The aforementioned costs and benefits of associations are predicted to shape movement decisions by influencing when orangutans tolerate or seek proximity to others versus when they prioritize being on their own and avoid associations. Each age-sex class of orangutan likely experiences a different balance of these costs and benefits. Oestrus females without dependent offspring actively seek mates, with associations primarily occurring for mating opportunities, however this can expose them to increased feeding competition, and also harassment from coercive mating attempts [ 17 , 22 , 28 ]. Mothers, in contrast, maintain prolonged associations to their dependent offspring [ 29 , 30 ], and seemingly adjust movement to reduce risk of harassment to the infant [ 5 , 31 , 32 ], prioritising offspring safety [ 17 ] over social opportunities. Flanged males, with their larger body size and secondary sexual characteristics, can monopolise access to food resources and females, influencing the movement of others [ 15 , 33 ], such as attracting females [ 34 ], and displacing other males [ 33 ]. However, because of their large body size, they face more pronounced energetic costs [ 34 ], which may limit their travel [ 9 ]. Unflanged males, on the other hand, being smaller, have lower energy demands, allowing them to allocate more energy toward searching for females. Adult females and flanged males are often resident individuals, therefore likely benefit from their greater knowledge and familiarity of the spatial distribution of resources, and social dynamics. Unflanged males, are more likely to be new to an area because of recent dispersal from their natal range leading to reduced spatial knowledge. Unflanged males are thus predicted to benefit from associating with more familiar individuals to acquire information on resource locations and social dynamics [ 35 , 36 ], although this entails risks such as displacement by dominant males and increased competition. Immature, and therefore likely more naïve, individuals are expected to benefit from associations by gaining social learning opportunities [ 37 , 38 ], important for the development of ecological competence [ 24 , 39 ]. However, they may face increased energetic costs associated with the increased exploratory behaviour, and likelihood of displacement by residents [ 35 ]. Across all classes, these trade-offs are likely to be context-dependent, with greater social tolerance at high-value (high abundance) feeding sites, whereby feeding competition and energetic costs are balanced by nutritional gains and temporary social advantages [ 18 , 40 ]. Studying spatial metrics offers a powerful tool for examining the costs and benefits of social associations. Previous research on primate movement ecology has demonstrated the influence of social factors on travel speed [ 41 – 43 ], route choice [ 44 ], foraging patch visitation [ 45 ], and resource competition [ 46 ]. However, these studies have typically focused on relatively broad social influences, such as group size, group cohesion and collective movement of group living species. Research on orangutan movement in particular has primarily focussed on individual-level spatial metrics, such as home ranges [ 47 – 52 ], and daily path lengths [ 47 , 49 ], treating individuals as solitary units, rather than temporally associating conspecifics and neighbours. As a result, few empirical studies have quantified how associate identity shapes spatial metrics in semi-solitary species such as orangutans, meaning the social drivers of these unique and ephemeral interactions are therefore often overlooked. In this study, we address this knowledge gap by investigating how the presence of different age-sex classes of conspecifics, and the time spent with them, shapes movement patterns and visitation of high value food sites of wild Sumatran orangutans ( Pongo abelii ). Specifically, we quantify spatial metrics - measurable properties of how individuals move through and use space, including the length and shape of daily travel paths and the use of high-value foraging locations. We then examine how the presence of mothers, independent immatures, flanged males, and unflanged males influences these spatial metrics. By integrating fine-scale movement data, with simultaneous behavioural observations, we aim to identify how the immediate social environment modulates movement behaviour. In doing so, we provide new insight into the costs and benefits of sociability. Based on the age-sex class specific costs and benefits of associations outlined above, we hypothesize that associations will differentially shape orangutan movement behaviour depending on the specific immediate social environment. As a result, we predict that both daily path length and path shape will vary systematically across age-sex classes and will shift as a function of time spent in association. Specifically, we predict that increased time in association will generally to lead to longer and more tortuous travel paths overall due to coordination demands and social interactions, whereas more solitary conditions should favour more direct and energy-efficient movement patterns. In particular, we predict that unflanged males increase path length and path sinuosity when in longer associations, reflecting mate-searching behaviour and limited spatial knowledge, whereas flanged males should show weaker social effects due to their social dominance and more pronounced energetic constraints. We further predict that mothers will reduce path length and adopt more direct (less sinuous) travel when associating with potentially risky partners such as adult males, reflecting efforts to balance infant protection, foraging efficiency, and avoidance of sexual coercion. Immatures should show reduced path length and increased linearity when associating with more spatially knowledgeable individuals. We further expect that associations alter visitation of high value food hotspots. In particular, we predict that increased time spent with others increases the number of foraging hotspots visited due to scramble competition and the need to seek alternative resources, but reduce residence time within a hotspot due to resource depletion. Finally, we expect these effects to be dyad-specific at the age-sex class level, with associations involving competitors increasing travel distance and reducing food resource residence time, and associations with potential mates, more tolerant or knowledgeable individuals producing more linear travel and shared space use. METHODS Data collection Between 2007 and 2023, we conducted focal follows on wild Sumatran orangutans ( Pongo abelii ) at the Suaq Balimbing field site within the Gunung Leuser National Park, in South Aceh, Indonesia (97.431°E, 3.050°N). We categorised individuals into four age-sex classes; unflanged males (adult males exhibiting arrested development), flanged males (adult males with secondary sexual characteristics such as cheek flanges), mothers (adult females with dependent immatures), and independent immatures (who range independently from their mother). We excluded unidentified individuals, and adult females of reproductive age without offspring, due to the brief duration of this reproductive state and insufficient sample size. We located focal individuals by systematically traversing predefined transects within the study area, while actively surveying for recent indicators of orangutan presence (e.g., feeding traces, nests), and auditory cues such as vocalizations or canopy movement. We recorded behavioural data at 2-minute intervals using standardised behavioural ethograms [ 53 ], and we logged corresponding GPS locations at 10-minute intervals, using handheld GPS devices. Behavioural data were collected from 110 individuals, including 39 unflanged males, 27 flanged males, 30 independent immatures, and 22 mothers. Of these, 72 individuals also had corresponding GPS data, comprising 20 unflanged males, 18 flanged males, 22 independent immatures, and 16 mothers. Over the course of the study, eight individuals were observed to transition between age-sex classes. We quantified movement using the following metrics: 1. Daily Path Length (DPL) : We estimated daily path lengths using the continuous-time speed and distance (CTSD) framework [ 54 ] in the ctmm R package [ 55 ]. Unlike conventional approaches that sum straight-line distances between successive GPS fixes, CTSD fits a continuous-time movement model to estimate mean speed, which is scaled by the daily observation duration to obtain distance travelled. This approach is robust to variation in sampling rate and path tortuosity [ 54 ]. To reduce inflation from GPS error, we incorporated an error model with a weakly informative prior on the root mean square (RMS) user equivalent range error (UERE) centred at 15 meters (95% credible interval: ~2–29 m), allowing error variance to be estimated jointly with movement parameters [ 56 ]. For each follow-day, the best-supported model was selected using AIC ( ctmm.select ), and daily path length was calculated as mean speed multiplied by sampling duration. 2. Sinuosity : Sinuosity is a measure of path tortuosity derived from the directional persistence and step length variation of the trajectory [ 57 ], where higher values indicate increasingly tortuous movement. Values were calculated using the trj_sinuosity2 function in the ‘trajR’ package [ 58 ]. $$\:Sinuosity=2\:[p\left(\frac{1+c}{1-c}\right)+{b}^{2}){]}^{-0.5}$$ Where p is the mean step length, c is the mean cosine of turning angles, and b is the coefficient of variation of the step length [ 57 ]. This method provides a corrected sinuosity index that generalizes the original formulation by Bovet & Benhamou (1988) [ 59 ] to accommodate a wider range of turning angle distributions and variable step lengths. 3. Number of feeding hotspots visited per day. 4. Time (minutes) spent in a feeding hotspot. We defined feeding hotspots as individual trees or small clusters of trees (within a 15 m crown radius) where the focal individual remained feeding continuously for more than 30 minutes. The distribution of feeding bout durations was strongly right-skewed, with a mean of 22 minutes and a modal duration of 9 minutes, revealing two distinct behavioural modes; brief sampling often whilst travelling, and prolonged feeding. Based on this distribution, we applied a conservative threshold of 30 minutes to define a feeding hotspot, as extended residence time likely reflects access to a particularly favourable food source of high abundance, when time spent feeding is used as a proxy for item value. 20.1% of feeding bouts lasted longer than 30 minutes. We measured total daily rainfall in millimetres, using a graduated measuring cylinder at a consistent open location at the research station, recorded at the same time each evening, representing rainfall during the day. We quantified fruit availability through monthly phenology surveys identifying fruit baring trees, performed at predefined transects spanning north to south and west to east throughout the study site, encompassing approximately 1000 trees with a diameter at breast height of > 20 cm. We calculated the proportion of fruiting trees and averaged this value to provide a monthly site-wide index of fruit availability. We analysed DPL, sinuosity and number of feeding hotspots per day using full-day focal follows, from departure from the sleeping nest to the construction of a new nest in the evening (nest-to-nest). For analyses of time spent in each hotspot, we also included shorter observation days to increase sample size, as these still captured complete feeding bouts within hotspots. For analyses of path length and sinuosity, we included only focal follows in which GPS data were available for at least 75% of the total active period length, to ensure paths were sufficiently complete and not biased by large temporal gaps. For each observation day, we calculated the total number of GPS waypoints recorded at 10-minute intervals as an index of sampling density, and included this variable as a control in analyses of sinuosity to account for variation in track resolution. Because sinuosity metrics depend on sampling density, we expected greater number of waypoints to inflate estimated sinuosity, as additional points capture more small-scale turns and deviations along the path. Because we expected longer active periods to correspond to greater hotspot use, reflecting increased opportunity for feeding during extended observations, we controlled for the active period duration (hours) in the analyses on hotspot usage. Path length estimates from CTMMs already account for sampling density. For each observation day, and during times spent in a feeding hotspot, we systematically recorded the presence or absence of associates from each of the four age-sex classes, along with percentage of time spent in association, thereby capturing the immediate social environment defined as the duration and composition of social associations. We considered associates present when they were located within 50m of the focal individual, a range that permits visual contact despite dense foliage. Given the potential for multiple associate classes to be present at the same time, we checked for multicollinearity among predictors. Model diagnostics indicated low variance inflation factors (VIFs), suggesting that the effects of different associate classes could be distinguished and were not strongly correlated. Analyses We quantified movement behaviour using four complementary metrics, each capturing a different aspect of spatial ecology: 1) daily path length (DPL) as a proxy for overall energetic investment in daily movement effort, 2) path sinuosity as a measure of movement efficiency, indicating whether travel was goal-directed or exploratory, 3) the number of feeding hotspots as a measure of key resource identification and utilisation, providing insights into spatial knowledge and potential cognitive maps, and 4) time spent in the feeding hotspot to assess resource exploitation and displacement from the hotspot. Together, these metrics link energy expenditure with spatial decision-making and resource use strategies. We implemented a three-tiered analytical framework to examine movement patterns at three different scales, considering focal age-sex class, immediate social environment and ecological factors (Fig. 1 ). We first analysed differences in spatial metrics across all focal age-sex classes (Population-level), to evaluate overall population-level effects of age-sex class and contextual variables. Secondly (Within-class level), we ran separate models for each focal age-sex class to capture within-class variation. This approach acknowledges that behavioural responses may not be uniform across age-sex classes, and it provides class-specific estimates while retaining the same set of predictors used in the population level analyses. Third, at a dyadic level, we evaluated how the presence of associates from each age-sex class influenced the movement of each focal (Dyadic-level). For population and within-class levels we included percentage of the day spent in association as a predictor. For the dyadic level analyses we used presence and absence rather than duration as this approach was more robust given limited sample sizes of some rare dyads ( Additional table 1 ). This approach is based on the assumption that mere presence of the associate can alter movement, regardless of association duration. Population level analyses involved the largest sample sizes and thus provided more robust population-level estimates. Building on this, within-class analyses allowed social and ecological predictors to have class-specific effects and capturing heterogeneity in behavioural responses, and the dyadic level analyses added critical understanding of dyad-specific variation, helping to explain the patterns detected at the prior levels. Full models were fitted including the factors of age-sex class, percentage of time in association, or associate presence, as predictors, in addition to control variables: fruit availability, rainfall, and, depending on the response variable, number of GPS waypoints, or active period duration. Random intercepts for focal ID accounted for repeated measures of individuals, and follow ID for multiple measures of hotspots per day. We used mixed effect models to account for the non-independence of repeated measures (i.e., multiple observations per individual and multiple daily records within individuals). We used linear mixed models (LMMs; lmer) for the response variables DPL, Sinuosity, and log-transformed Time spent in a hotspot as they were continuous and approximately normally distributed. For the number of hotspots visited per day (as a count variable), we used generalised linear mixed models (GLMMs; glmmTMB) with a Conway-Maxwell Poisson distribution. We used packages ‘lme4’ [ 60 ] to fit LMMs, and ‘glmmTMB’ [ 61 ] to fit GLMM models, with appropriate diagnostic checks performed to verify model assumptions. Detailed model structures and sample sizes are provided in Additional table 1. All analyses were conducted in R [ 62 ]. We used Likelihood Ratio Tests (LRTs) via the anova function to compare full models (containing all predictors and random intercepts) to null models (containing only random intercepts). We assessed significance of fixed effects using Type III Wald χ² tests, and we conducted Tukey-adjusted post-hoc pairwise comparisons [ 63 ] to evaluate differences among age-sex classes. To complement quantitative analyses of movement and association patterns, we also investigated behaviours occurring during the recorded associations. We calculated activity budgets by summarising the percentage of time the focal spent feeding, resting, moving, nesting, socialising, and engaging in other behaviours, when with an associate, per follow, and then averaged per age-sex class dyad. We identified which individual initiated and which followed in each movement bout to distinguish individuals seeking social opportunities from those serving as the target. For each follow, we calculated the daily proportion of bouts in which the focal led or followed, then averaged these values across age-sex class dyads to ensure equal weighting. By linking movement and foraging behaviour to its social context, we provide a rare test of how the presence and class of associates modulates animal decision-making. RESULTS Population-level effects of associations and age-sex class on movement and foraging patterns On average, orangutans at Suaq Balimbing were alone 53.6% of the time, and with 1 other individual (excluding dependent immatures) 26.9% of the time, and with 2 or more individuals 19.6% of the time. In particular, independent immatures were the most social class, being with at least one associate 57.9% of the time, followed by unflanged males (50.0%) and mothers (46.1%), whereas flanged males were with an associate only 32.7% of the time. Daily path length : Orangutans at Suaq Balimbing travelled 1130 m per day on average (± 503m SD) when alone, but the more time they spend in social associations the farther they travel each day (1201m on average when in association all day; ±425m SD). A likelihood ratio test (LRT) indicated that the full model explained significantly more variation in daily path length (DPL) than the corresponding null model (χ²(6) = 18.103, p = 0.006). Time spent in association (χ²(1) = 4.58, p = 0.032) showed a significant positive effect on DPL (Fig. 2 ). Age-sex class also had a significant overall effect on DPL (χ²(3) = 8.53, p = 0.036); however, Tukey-adjusted pairwise comparisons of estimated marginal means revealed no significant differences between specific classes (all p > 0.05), suggesting that while class explains some variance in path length, no individual class differs clearly from the others. Fruit availability had a significant positive effect on DPL (χ²(1) = 3.88, p = 0.048). Rainfall did not significantly affect DPL. Complete model outputs are provided in Additional table 2. To determine whether longer paths were mediated by associate presence leading to longer observational periods, we re-ran the full model on DPL, with the inclusion of active period duration as a control variable. The results revealed no significant effect of time in association in this model (Additional table 3), signifying that individuals that spend more time in association do not travel farther per unit time, but they are active for longer, which results in greater total movement distances. Sinuosity of the daily path : Orangutans’ paths became straighter when individuals were with associates, and unflanged males in particular tended to travel in more linear trajectories than mothers. The full model explained significantly more variation in path sinuosity than the corresponding null model (χ²(7) = 63.538, p < 0.001). Model results showed a trend towards a negative effect of time spent in association on daily path sinuosity (χ²(1) = 3.76, p = 0.053) (Fig. 2 ). The overall effect of age-sex class on trajectory sinuosity was significant (χ²(3) = 18.44, p < 0.001). Post-hoc pairwise comparisons showed that mothers had significantly higher sinuosity than unflanged males (mean difference = 0.039, p < 0.001), whereas all other pairwise contrasts were not significant. Fruit availability and rainfall did not significantly affect daily path sinuosity. Daily path sinuosity increased with the number of waypoints recorded per day (χ²(1) = 43.80, p < 0.001) (Additional table 4). Number of feeding hotspots visited per day : Orangutans generally focused on a few key feeding sites per day, which varies per age-sex class (on average, the mean observed number of hotspots visited per day was 5.4 for flanged males, 4.8 for mothers, 4.6 for independent immatures, and 4.4 for unflanged males), with fewer hotspots visited when in association. The full model explained significantly more variation in the number of hotspots visited per day compared to the corresponding null model (χ²(7) = 59.957, p < 0.001). There was a significant negative effect of time spent in association on the number of feeding hotspots visited per day (χ²(1) = 25.79, p < 0.001) (Fig. 2 ). Age-sex class had a significant overall effect on the number of hotspots visited per day (χ²(3) = 15.77, p = 0.001). Post-hoc comparisons indicated that flanged males visited more hotspots than independent immatures (rate ratio = 1.18, p = 0.003), mothers (rate ratio = 1.15, p = 0.021), and unflanged males (rate ratio = 1.20, p = 0.014), while all other pairwise contrasts were not significant. The number of hotspots visited per day increased significantly with active period duration (χ²(1) = 21.74, p < 0.001). Fruit availability and rainfall did not significantly affect the number of hotspots visited per day. Time spent in feeding a hotspot : Orangutans spent less time at a feeding hotspot when associating with others, and the extent of this varied per age-sex class. The observed mean time spent in a hotspot was 57 minutes for flanged males, 54 minutes for unflanged males, 52 minutes for mothers, and 51 minutes for independent immatures. The full model explained significantly more variation in time spent in a feeding hotspot than the corresponding null model (χ²(7) = 34.49, p < 0.001). Model results showed a significant negative effect of time spent in association on the time spent in a hotspot (χ²(1) = 13.31, p < 0.001) (Fig. 2 ). Age-sex class had a significant overall effect on time spent in a hotspot (χ²(3) = 15.12, p = 0.002). Post-hoc comparisons of estimated marginal means (back-transformed from the log scale) indicated that flanged males spent significantly longer (~ 6–8%) in a hotspot than independent immatures (ratio = 1.08, p = 0.002) and mothers (ratio = 1.07, p = 0.009), while all other pairwise contrasts were not significant. Active period duration, fruit availability, and rainfall did not significantly affect time in a hotspot. Panels show the relationship between the percentage of time spent in association per day and (a) daily path length, (b) daily path sinuosity, (c) number of feeding hotspots visited per day, and (d) time spent in a feeding hotspot. A value of 0% time in association represents days when the focal individual was alone. The black line represents the population-level average, while coloured lines denote individual age-sex classes. Lines are derived from model-estimated values with all predictors, except time in association, held at their mean (estimated using the emmeans() function in R), and shaded ribbons indicate 95% confidence intervals. Asterix represents significant effect of % Time in association (p < 0.05), n.s = non-significant. Within-class effects of associations on movement and foraging patterns Daily path length : Within classes, individuals did not consistently increase their daily travel distance when spending more time in association (Fig. 3 ). For unflanged males, the full model on DPL did not explain significantly more variation than the respective null model (χ²(3) = 7.689, p = 0.053), although there was a trend. The full model revealed a positive effect of time spent in association on daily path length (χ²(1) = 4.951, p = 0.026). For flanged males (χ²(3) = 7.123, p = 0.068), mothers (χ²(3) = 1.095, p = 0.778), and immatures (χ²(3) = 0.623, p = 0.890), the full models did not explain more variance in daily path length than the respective null models. Fruit availability and rainfall had no significant effects on DPL in any class (all p > 0.05). Sinuosity of the daily path : Within age-sex classes, path shapes were generally unaffected by time spent in association (Fig. 3 ). The full model explained significantly more variance in daily path sinuosity than their corresponding null model for unflanged males (χ²(4) = 14.297, p = 0.006), flanged males (χ²(4) = 18.161, p = 0.001), and mothers (χ²(4) = 28.73, p < 0.001), but not for independent immatures (χ²(4) = 2.158, p = 0.707). Time spent in association did not significantly affect sinuosity in any class, however, across classes, the total number of waypoints per path consistently positively affected sinuosity (unflanged males: χ²(1) = 7.74, p = 0.005; flanged males: χ²(1) = 15.19, p < 0.001; mothers: χ²(1) = 25.36, p < 0.001). Rainfall reduced path sinuosity for unflanged males (χ²(1) = 4.514, p = 0.034). Fruit availability had a positive effect on sinuosity for flanged males (χ²(1) = 6.059, p = 0.014). Number of feeding hotspots visited per day : Flanged males and mothers visited fewer feeding hotspots when associating with others, while unflanged males and immatures showed no clear social effect (Fig. 3 ). The full model explained significantly more variance in the number of feeding hotspots visited per day than the corresponding null model for flanged males (χ²(4) = 18.04, p = 0.001) and mothers (χ²(4) = 19.76, p < 0.001), but not for unflanged males (χ²(4) = 5.15, p = 0.272) or immatures (χ²(4) = 8.56, p = 0.073). For both flanged males and mothers, time spent in association negatively affected the number of hotspots (flanged males: χ²(1) = 9.67, p = 0.002; mothers: χ²(1) = 9.67, p = 0.002). Active period duration had a positive effect on the number of hotspots for both flanged males (χ²(1) = 9.97, p = 0.002) and mothers (χ²(1) = 11.09, p < 0.001). Fruit availability and rainfall had no significant effect on the number of hotspots visited for any class. Time spent in feeding a hotspot : Flanged males spent less time at a feeding hotspot when associating with others, whereas unflanged males, immatures and mothers’ hotspot visitation duration was unaffected by social context (Fig. 3 ). The full model explained significantly more variance in the time spent in a feeding hotspot than the corresponding null model for flanged males (χ²(4) = 13.81, p = 0.008) and marginally so for independent immatures (χ²(4) = 9.46, p = 0.051). For unflanged males and mothers, the full model did not explain significantly more variance than the null model (unflanged: χ²(7) = 4.7473 p = 0.691; mothers: χ²(4) = 2.90, p = 0.575). Time spent in association at the hotspot negatively affected hotspot duration for flanged males (χ²(1) = 9.16, p = 0.002) and immatures (χ²(1) = 8.02, p = 0.005). Active period duration, fruit availability, and rainfall had no significant effects for any class. Panels show the relationship between the percentage of time spent in association per day and (a) daily path length, (b) daily path sinuosity, (c) number of feeding hotspots visited per day, and (d) time spent in a feeding hotspot. A value of 0% time in association represents days when the focal individual was alone. Coloured lines represent each age-sex class, with separate slopes for each. Asterix represents a significant effect of % Time in association (p < 0.05), coloured per age-sex class. Lines are derived from model-estimated values with all predictors, except time in association, held at their mean (estimated using the emmeans() function in R), and shaded ribbons indicate 95% confidence intervals. Dyadic effects of focal–associate class combination on movement and foraging patterns Daily Path Length : Mothers adjusted their daily travel distances depending on which associates were present, whereas immatures, unflanged and flanged males’ distances were unaffected by different classes of associates. The full models explained significantly more variance in DPL than the corresponding null models for mothers (χ²(6) = 14.672, p = 0.023), but not for immatures (χ²(6) = 3.655, p = 0.723), unflanged males (χ²(6) = 5.560, p = 0.474) or flanged males (χ²(5) = 3.424, p = 0.635). For Mothers, the presence of flanged males (χ²(1) = 7.733, p = 0.005) affected DPL, while the presence of other classes did not (Fig. 4 ). Fruit availability and rainfall had no significant effect. Sinuosity of the daily path : At the dyadic level, different classes of association partners had generally limited effects on path sinuosity, although unflanged males’ trajectories became more sinuous in the presence of immatures, and mothers’ trajectories became less sinuous in the presence of flanged males. The full models explained significantly more variance in path sinuosity compared to the null models for unflanged males (χ²(7) = 17.06 p = 0.017), flanged males (χ²(6) = 13.93, p = 0.030), and mothers (χ²(7) = 9.27, p = 0.234), but not for immatures (χ²(7) = 6.30, p = 0.505). For unflanged males, path sinuosity was positively affected by number of waypoints (χ²(1) = 8.19, p = 0.004), and rainfall (χ²(1) = 4.38, p = 0.036). For flanged males, path sinuosity was positively affected by number of waypoints (χ²(1) = 8.39, p = 0.004). For mothers, path sinuosity was positively affected by flanged males (χ²(1) = 4.01, p = 0.045), fruit availability (χ²(1) = 4.33, p = 0.038), and number of waypoints (χ²(1) = 33.84, p < 0.001) (Fig. 4 ). Number of feeding hotspots visited per day : Mothers visited fewer feeding hotspots when male associates were present, whereas flanged and unflanged males and immatures’ hotspot use was largely unaffected by different classes of associates. For mothers, the full model explained significantly more variance in the number of feeding hotspots visited per day than corresponding the null model (χ²(7) = 27.35, p < 0.001). Mothers visited fewer hotspots when unflanged males (χ²(1) = 9.23, p = 0.002) or flanged males (χ²(1) = 4.06, p = 0.044) were present (Fig. 4 ), while follows of longer duration were associated with a greater number of hotspots visited (χ²(1) = 15.21, p < 0.001). Other predictors were non-significant. For unflanged males, flanged males and independent immatures, the full models did not explain significantly more variance in hotspot use than the null models. Time spent in a feeding hotspot : Mothers adjusted how long they stayed at a feeding hotspot depending on the class of the associate, whereas hotspot durations were unaffected by the presence of different classes of associates for the other focal classes. For mothers, the full model explained significantly more variance in the time spent in a feeding hotspot than the null model (χ²(7) = 19.95, p = 0.006). The presence of flanged males increased mothers’ time in a hotspot (χ²(1) = 12.01, p < 0.001), whereas the presence of other mothers decreased it (χ²(1) = 4.49, p = 0.034). Other predictors, including the presence of unflanged males, immatures, fruit availability, active period duration, and rainfall, had no significant effects. All other predictors were non-significant. For unflanged and flanged males, likelihood ratio tests indicated that the full models did not explain more variance than the null. Activity Budget : The dyad-specific activity budgets revealed differences in how focal individuals allocate time across behaviours depending on their associate. Feeding was the most prevalent behaviour across all focal individuals; this pattern held true for every focal-associate dyad as well as when individuals were alone (Fig. 5 ) . The highest proportion of time spent moving was when flanged males were in association with unflanged males (22.0%), whereas their movement was lowest (15.8%) when with other flanged males. Resting was most prominent for flanged males, peaking at 24.8% when with independent immatures, though least for independent immatures overall (14.8–19.6%). Social interactions were generally rare, with independent immatures consistently allocating the least time (0.3–0.7%). Notably the highest proportion of social behaviour was when flanged males associated with unflanged males (2.6%), primarily in the form of social watching and social aggression towards the associate. Movement order : Analysis of movement sequence behaviour revealed the proportion of times the focal followed associates or led movement bouts. Independent immatures generally led movement when paired with flanged and unflanged males, but tended to follow mothers (Fig. 6 ). Mothers led movement more often than followed regardless of associate class. Flanged males tended to follow mothers, while unflanged males tended to follow associates from all classes, except in the presence of flanged males, where proportions were more equal. DISCUSSION By integrating fine-scale movement data with detailed behavioural observations, we move beyond describing how orangutans travel, to explaining why they make these movement decisions. This study provided a multidimensional view of how orangutans dynamically adjust movement in response to their immediate social environment and, in doing so, sheds novel light on the costs of sociality. This socially responsive movement supports predictions that this semi-solitary ape experiences measurable locomotor and foraging trade-offs when associating with conspecifics, and also that these trade-offs vary across age-sex classes. Previous research shows that orangutan associations vary across age-sex class [ 5 , 16 ], reproductive state [ 17 ], and habitat productivity [ 10 , 18 ]. In line with this, our analyses identified the immediate social environment as a consistent driver of movement decisions, with effects varying between focal-associate dyads. Effects of associations on daily path length We predicted that time spent in association increases daily path length due to coordination demands and social interactions, whereas solitary conditions favour more direct and energy-efficient movement. Our results partially supported this prediction, showing that sociality imposes a measurable locomotor cost for orangutans: individuals travelled farther on days with greater social engagement (population level analyses), but this effect was not consistent across all age-sex classes and social contexts. Unflanged males generally travelled the farthest, followed by immatures, flanged males, and then mothers. For unflanged males, long paths likely reflect mating strategies involving active tracking and monitoring of potential mates. Moreover, unflanged males typically have less familiarity with the area, and must therefore expand their knowledge of the distribution of resources and conspecifics, through exploration similar to immatures, after dispersing out of their natal range to avoid inbreeding [ 7 ]. Similarly, long paths for immatures are consistent with the exploratory ranging behaviour of dispersing immatures, who must gain spatial knowledge of resource distribution during the development of ecological competence [ 64 , 65 ], and home range establishment [ 65 ]. However, the absence of reduced travel distance during associations, even with knowledgeable residents, may indicate that immatures do not use others’ spatial knowledge to optimise movement. It is also possible that the influence of associates varies across immature age and was therefore not captured in the present model. Longitudinal or cross-sectional analyses would help determine whether immatures benefit from associations at specific ages. Mothers and flanged males, who often have established stable home ranges, and are therefore more knowledgeable of resource locations, are constrained by the need to balance energy expenditure against foraging gains and thus have shorter paths overall. Mothers in particular bear the high costs of pregnancy and offspring care, whilst flanged males mostly bear the cost of large body size, therefore prioritise energy conservation. Importantly, at the population level, increased daily path length reflected longer periods of activity rather than faster movement. This indicates that individuals in social contexts do not necessarily move more intensively, but instead remain active for longer periods, resulting in greater total daily travel distances. Given the high energetic costs of locomotion in orangutans, driven by their large body size and arboreal lifestyle, even modest increases in daily travel may create significant energetic costs [ 66 ]. Dyadic analyses further highlighted that the effects of social context are partner-specific. Mothers increased their daily path length when in the presence of flanged males. Females are generally thought to preferentially associate with flanged males as mating partners, while tending to avoid unflanged males, which are more often associated with coercive mating attempts. Consequently, longer paths when with flanged males may reflect mate seeking behaviour driven by female choice. Longer movement paths away from males, prioritising infant protection, would be expected to be more pronounced in the presence of unflanged males. However, flanged males that are newly immigrated or only recently attained dominance likely have a lower probability of paternity and could therefore represent a potential threat to infants [ 67 ]. This cost is further reflected in mothers leading movement bouts during their longer daily paths to avoid flanged males. Subsequently, associations with males can impose costs on females, reflecting a form of sexual conflict, with variation depending on male morph and context, aligning with published research on costs of associating with males [ 15 ]. In this light, our findings suggest that mothers adjust their movement not simply in response to associate presence per se, but according to the perceived risks and benefits associated with flanged males. The absence of dyadic effects in immatures and both flanged and unflanged males may indicate that social influences on path length are only expressed during periods of coordinated travel. Across the full day, other activities such as resting, feeding, or socialising with an associate may not substantially affect overall path length or its structure. Moreover, there were no data available on the presence of flanged males with other flanged males for full-day observations with sufficient GPS data, which provides some evidence for avoidance behaviour between the dominant males. Moreover, activity budget behavioural data revealed that when flanged males and unflanged males associated with other flanged males, they had the highest proportions of time spent travelling, and the greatest reduction in time spent feeding, compared to other dyads, providing further evidence for avoidance and displacement behaviour, and subsequent energetic costs. Effects of associations on daily path sinuosity We predicted that increased time spent in association would increase path sinuosity due to the need to coordinate movement decisions, or avoid others. Results showed that path sinuosity appeared relatively stable across immediate social environments but differed among age-sex classes. This suggests that while social factors such as feeding competition or the opportunity to benefit from another’s spatial knowledge do not influence the directness of travel routes, energetic requirements and nutritional needs may. At the population level, mothers exhibited more sinuous paths than unflanged males, which most likely reflects contrasting ranging strategies. Mothers may adopt more sinuous movement patterns as they forage intensively within localised areas, repeatedly revisiting resource patches to meet the high energetic demands, and potential nutrient requirements of pregnancy, lactation [ 68 – 70 ] and infant care, while minimising travel costs. Mothers may also deviate from spatially efficient travel paths, as they must select routes with smaller canopy gaps that allow offspring to cross [ 71 ], and occasionally return to retrieve them if they fall behind. More linear movement paths in unflanged males may reflect direct, goal-oriented travel toward resources or social targets, potentially increasing encounters with receptive females. Such straighter trajectories could indicate a strategy that enhances encounter rates while improving travel efficiency, thereby offsetting the energetic costs of their long daily paths. This interpretation contrasts with the expectation that unflanged males have limited spatial knowledge, instead suggesting they can navigate their environment efficiently. Overall, dyadic social context had varying effects on path sinuosity. Some class-specific associations were evident (e.g., increased sinuosity in unflanged males in the presence of immatures and reduced sinuosity in mothers when accompanied by flanged males). Taken together, these results suggest that path sinuosity is primarily structured by focal age-sex class, but also the immediate social environment can shape movement patterns in specific contexts. Effects of associations on feeding hotspot use We predicted that sociality would increase the number of feeding hotspots visited due to scramble competition, and reduce the time spent at each hotspot because of resource depletion. At the population level, our results showed that foraging behaviour, as measured by hotspot visitation and time spent in each hotspot, varied across immediate social environments and between age-sex classes. Contrary to our predictions, individuals visited fewer hotspots as time in association increased and also spent less time at each hotspot (population level analyses). These findings provide detailed insight into feeding competition, suggesting that individuals do not compensate for visiting fewer hotspots by prolonging their visits. Instead, sociality appears to constrain both the breadth and intensity of resource exploitation. However, this pattern may also partly reflect a methodological effect driven by patch depletion rates. When individuals are in association, increased feeding competition may lead to faster resource depletion, resulting in shorter visits that fall below the threshold required for a location to be classified as a hotspot. In contrast, when alone, individuals may exploit the same patches for longer due to lower depletion rates, increasing the likelihood that these locations are identified as hotspots. Thus, some patches with high resource potential may be underrepresented as hotspots in social contexts, potentially exemplified by our result of fewer hotspots visited and less time spent in them when in longer associations. Age-sex class differences were also evident, flanged males exploited the greatest number of feeding hotspots, and also spent more time in them, than the other age-sex classes. This pattern may reflect greater local knowledge, and a strategy of exploiting and exhausting foraging resources without the added costs of searching for alternative resources, given the high energetic costs of locomotion in flanged males [ 34 , 70 , 72 ]. The social dominance of flanged males also likely allows them to monopolise resources and therefore displace associates. However, despite exploiting hotspots the most, as the percentage of time spent in association increased, they visited fewer hotspots, and spent less time in them (within-class level analyses). Similar effects were seen for mothers, who visited fewer hotspots as association time increased, and immatures, whose time spent in a hotspot also decreased when spending longer time in associations. We found several dyad-specific trends suggesting that the class of associates may differentially influence levels of feeding competition and evidence for individuals’ strategies to compensate for it (dyadic level analyses). For instance, mothers visited less hotspots when around flanged and unflanged males, but extended hotspot residence time in the presence of flanged males. This result suggests that mothers compensate for the reduced number of hotspots visited when with flanged males by exploiting them more thoroughly, consistent with energy conservation strategies. This result may also reflect increased social tolerance between females and flanged males. Females regularly actively seek the presence of flanged males [ 17 , 27 ] whereas they tend to avoid unflanged males who actively seek and often perturb them [ 73 ]. Orangutan mothers are known to display high levels of social tolerance to other females and immatures, especially their close relatives [ 74 – 76 ]. However, the results of this current study reveal that the presence of mothers reduces time in a hotspot in other mothers. This highlights that competition and resource depletion are likely the key drivers of foraging patch exploitation, when mating benefits are absent. Examining dyad-specific associations revealed that the class of social partners, rather than sociality as a whole, plays a critical role in shaping movement and foraging behaviour for some age-sex classes, particularly mothers. In contrast, adult males, particularly flanged males, showed relatively limited sensitivity to the identity of associates, suggesting greater autonomy in their movement and foraging decisions. Social modulation of activity budgets and movement initiation Overall, being in association did not substantially alter the pattern of activity budgets. Across all contexts, whether alone or with different classes of associates, individuals devoted the largest proportion of their time to feeding (around 50–60%), followed by movement and resting. However, associations may influence the functional basis of these activities. Feeding in close proximity to associates may be particularly important for spatially naïve individuals, such as immatures and unflanged males, by facilitating the acquisition of food locating, and extractive foraging skills. Travel with partners may enhance spatial learning of resource distribution, while resting alongside associates may provide opportunities for observational social learning. Overall, associations generally led to a larger proportion of the activity budget spent moving, longer total active periods, and consequently increased path length, all of which carry energetic costs. However, individuals did not appear to offset these costs by increasing energy intake by spending more time feeding. Flanged males in particular faced the greatest reduction in time spent feeding when associating with unflanged males. Instead, there was a modest increase in time allocated to resting, socialising, and other activities (such as independent exploration, and long-call vocalisations). Movement bout order adds another layer of evidence to what factors underly movement decisions. Following an associate can create opportunities for social learning, particularly from more knowledgeable individuals, whereas leading the movement shows active spatial decision making. Patterns of dyadic movement order were consistent with female mate choice and the contrasting mating strategies of the two male morphs; unflanged males tended to follow mothers, and to a lesser extent immatures, consistent with their strategy of seeking mates. Females instead tended to seek out flanged males, reflecting their mating preference. Unflanged males were frequently displaced when in associations with flanged males, a pattern reflected in the proportions of movement bouts and the lack of these dyadic associations in general. Independent immatures were the most social class, with an associate more often than alone, though engaged in relatively little direct social interactions, compared to the other age-sex classes. Despite limited direct interactions, their greater level of sociality may confer indirect social benefits: by being within sight of more experienced individuals, they could gain access to information about resource locations, conspecific location, or predator avoidance without the costs of direct interaction or conflict. In this way, social association acts as a low-risk learning environment, allowing immatures to benefit from the knowledge and experience of others. They followed tolerant or knowledgeable resident individuals [ 77 ], especially their own mothers [ 23 ], but seemed to avoid potentially risky males, indicating selective social use of information. This combination supports published literature stating an exploratory [ 14 , 65 , 78 ], learning oriented [ 64 ] movement strategy. Conversely, flanged males were the least social class, though when with an associate, they did invest more time in direct social behaviour, particularly mating and observing mothers, and displaying aggression to other males. Their large body size and social dominance suggests priority access to resources and reduced need to modify travel due to associates, aligning with an energy-conserving, dominance-based movement strategy. Mothers had a more stable activity budget regardless of associate class, and they frequently led movement, likely avoiding costly associations [ 5 ]. They were sensitive to associate identity, reflected with their longer daily paths, and use of fewer foraging hotspots when with flanged males, but varied time spent in a hotspot depending on associate class. Together, these patterns indicate an energetic conservation and infant protection driven strategy shaped by the demands of caregiving. Unflanged males varied in their allocation of time to social behaviours depending on the age-sex class of the associate, likely due to seeking mates and avoiding rival males. Interestingly, unflanged males and independent immature dyads devoted the highest proportion of time in association to feeding, which likely helps these classes, who have relatively limited knowledge of resource locations, share information about where to find food. Overall, these patterns suggest that associations actively structure behavioural investment and learning opportunities across age-sex classes. Ecological effects on movement and foraging behaviour Interestingly, ecological variation, specifically fruit availability, did not have a consistent influence on movement, despite the largest proportion of the active period devoted to foraging and consuming food. Only some age-sex class specific ecological effects emerged at the within-class level analyses, such as unflanged males travelling more direct under challenging environmental conditions of increased rainfall, and flanged males increasing path sinuosity to exploit higher fruit availability in the local area, consistent with more localised searching or patch use when resources are abundant. This absence of consistent effects of fruit availability may be specific to the Suaq Balimbing site, which benefits from relatively high and stable food availability, compared to other orangutan research sites. Similar observations have been reported in other studies at Suaq, such as when alternative measures of fruit availability (eFAI; which calculated the actual fruit availability experienced by the individual, rather than habitat-level availability) showed minimal effects on ranging [ 79 ]. A different study on the same population found that fruit availability did not show any impact on day journey length [ 47 ], whereas another found contrasting results on male path length [ 80 ]. Moreover, additional studies found that fruit availability at Suaq Balimbing was not strongly linked to party size [ 5 ], insect-feeding preferences [ 81 ], or social play [ 25 ], in contrast to other sites where stronger effects have been observed. Hence, the effects of fruit availability are likely to be less pronounced at Suaq than other sites. Limitations Several limitations should be considered. The number of GPS waypoints strongly influenced sinuosity, so we included it as a control covariate because it correlates with both active period duration and data resolution. While active duration limits total movement, resolution directly affects calculated metrics by capturing more fine-scale path deviations, making this control essential to distinguish biological from methodological effects. However, the nature of the effect of the number of way points on sinuosity would need to be explored in detail to assure that adding it as a linear control is the best practice. Importantly, the observed age-sex differences in movement remained robust after accounting for waypoint number, indicating that our main conclusions are driven by genuine behavioural differences rather than artefacts of active period duration or GPS sampling density. Secondly, dyad-specific analyses varied in sample size, particularly for males, whereby low sample size itself provides evidence for social intolerance, but also reduced power to detect subtle social effects. The absence of significant effects in the current data set therefore does not fully rule out their presence. Conversely, because of sample size limitations, we did not control for repeated testing, for example by adjusting our significance threshold [ 82 ]. While it is common practice for studies with sample size limitations to not adjust significant thresholds to avoid reducing statistical power, it does inflate the risk of false positive effects. Finally, fruit availability, though a method consistent within published literature, is measured at relatively course temporal scales, which do not accurately reflect fine-scale resource depletion, or orangutans dietary preference. Future work integrating high resolution resource mapping may reveal additional ecological influences not captured in this study. CONCLUSION By using orangutans as a model system and leveraging an exceptionally detailed long-term dataset on movement and behaviour, we generated broader insights into the energetic costs of social associations, in relation to movement and foraging, and the mechanisms through which potential benefits can offset them. As semi-solitary apes that, due to their large body size and arboreal lifestyle, face pronounced energetic constraints [ 70 ], orangutans provide a valuable framework to investigate the costs and benefits of social association [ 10 , 13 , 83 ]. Our study concludes that Orangutan movement is best understood as demographically structured (age-sex driven) and individually expressed, yet socially shaped in many aspects. Social interactions may influence when and how far individuals travel, and how they utilize foraging hotspots, but they do not appear to strongly restructure the fine-scale geometry of daily movement paths. This study sheds novel light on the mechanisms underlying feeding competition as well as how these costs of associations are dynamically weighted by the benefits of spatial knowledge sharing, such as skill acquisition [ 14 , 37 ], enhanced discovery of resources [ 39 ], protection from harassment [ 5 ], and mating opportunities [ 12 , 22 ]. More broadly, these results contribute to the growing evidence that even species traditionally characterised by their semi-solitary nature, exhibit socially responsive movement strategies, akin to those observed in more gregarious species, challenging simple dichotomies between solitary and group living species. By integrating spatial metrics with fine-scale behavioural data, such as activity budgets and order of movement bouts, we were able to move beyond describing how individuals move, to shed novel light on why . Taken together, our study emphasises that trade-offs between costs and benefits of associations are flexible and context dependent, and should be considered central to understanding ranging behaviour. Recognising this socially mediated flexibility is particularly important for conservation, as changes in population density particularly in fragmented habitats may alter these trade-offs and, consequently, the energetic balance of individuals. Abbreviations DPL Daily Path Length LMMs Linear mixed models GLMMs Generalised linear mixed models LRTs Likelihood ratio tests HS Hotspot ANOVA Analysis of variance i.e. Id est n Number m Meters χ² Chi-squared statistic CTSD Continuous-time speed and distance CTMM Continuous time movement model Declarations Ethics approval and consent to participate : Research was conducted in compliance with relevant institutional and national guidelines, and approved by The National Research and Innovation Agency’s ethics committee (BRIN Ethical clearance Ref No.: 026/KE.02/SK/8/2022) Consent for publication : Not applicable. Availability of data and materials : The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Competing interests : The authors declare that they have no competing interests. Funding : This research was supported and funded by the Max Planck Institute of Animal Behavior (C.S., E.L.), University of Zurich (C.S.), the A.H. Schultz Foundation (C.S.), the Leakey Foundation (Primate Research Fund and project grant) (C.S.), the SUAQ Foundation (C.S.), the Volkswagen Stiftung (Freigeist fellowship to C.S.), the Stiftung für Mensch und Tier (Freiburg i.Br. to C.S.), and the International Max Planck Research School for Quantitative Behaviour, Ecology and Evolution (IMPRS-QBEE)(E.L). Authors' contributions : E.L contributed to data collection, conducted statistical analyses, interpreted the data, wrote and edited the manuscript, created plots and visualisations. C.S contributed to data collection, provided conceptual guidance and contributed to editing the manuscript. S.S.U.A. provided administrative support. O.J contributed to movement data analysis. All authors commented on and approved the final manuscript. Acknowledgements : We acknowledge the help and support of the National Research and Innovation Agency (BRIN) and the Gunung Leuser National Park (TNGL) for the permission and essential administrative support provided to conduct this long-term research at the Suaq Balimbing Research Station. We also thank our affiliated institutions: the Magister of Biology Program, Faculty of Biology and Agriculture, Universitas Nasional, Jakarta, and the Max Planck Institute of Animal Behaviour, Germany, for their support. We thank YEL (Yayasan Ekosistem Lestari) and SOCP (Sumatran Orangutan Conservation Programme) for their collaboration, for hosting our project at the Suaq Balimbing Research station, and their contributions to supporting the research and conservation efforts in area. 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Springer US; 1987 [cited 2018 Jun 13];8:17–41. https://doi.org/10.1007/BF02737112 Additional Declarations No competing interests reported. Supplementary Files ADDITIONALINFORMATION.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 06 May, 2026 Reviewers invited by journal 04 May, 2026 Editor assigned by journal 04 May, 2026 Submission checks completed at journal 04 May, 2026 First submitted to journal 30 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9574845","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":636023964,"identity":"b67069b9-adeb-4c47-96c1-46e8bc7400b0","order_by":0,"name":"Emma Lokuciejewski","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFElEQVRIiWNgGAWjYDACdgZmICnBwNjAAMQGNgwGEHFm3FqYUbWkEa0FAoDaDhPWws/MfNiYp8ZCjrm9x/jjjILz8uYM3GkPvzBYy+HSItnMlpzMc0zCmLHnjJnkBoPbhjsbeLcbyzCkG+PSYnCYx/gwb4NEYuOM3G2MDwxuM244wLtNWoLhcGIDDi32UC31jfPfbv74wOCcPUxLPS4tBsw8xslALQmMM3g3AB12IBGkRfIDw+EEXA6TOMyWbDjnmIRhY0/+N8kZBsnJO5uBfmEwSDfEZQt/e/NhiTc1dfKG7ceSP/b8sbPdzt677eGPCmt5XLbAAcJQZgY2Zh4DghoYGJANZWP8QYSOUTAKRsEoGDEAALynU1KBktGSAAAAAElFTkSuQmCC","orcid":"","institution":"Max Planck Institute of Animal Behavior","correspondingAuthor":true,"prefix":"","firstName":"Emma","middleName":"","lastName":"Lokuciejewski","suffix":""},{"id":636023969,"identity":"4553a58a-c616-467a-aa58-917a52dd7c10","order_by":1,"name":"Margaret Crofoot","email":"","orcid":"","institution":"Max Planck Institute of Animal Behavior","correspondingAuthor":false,"prefix":"","firstName":"Margaret","middleName":"","lastName":"Crofoot","suffix":""},{"id":636023974,"identity":"a5c4ed99-d6c9-47aa-bb73-8915b769b5ca","order_by":2,"name":"Maria van Noordwijk","email":"","orcid":"","institution":"Max Planck Institute of Animal Behavior","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"van","lastName":"Noordwijk","suffix":""},{"id":636023976,"identity":"e3b1905e-0948-4a26-9791-f2e5b01fb01a","order_by":3,"name":"Odd Jacobson","email":"","orcid":"","institution":"Max Planck Institute of Animal Behavior","correspondingAuthor":false,"prefix":"","firstName":"Odd","middleName":"","lastName":"Jacobson","suffix":""},{"id":636023981,"identity":"837d7b0c-d6cd-4def-a677-c8568b430b3d","order_by":4,"name":"Carel van Schaik","email":"","orcid":"","institution":"Max Planck Institute of Animal Behavior","correspondingAuthor":false,"prefix":"","firstName":"Carel","middleName":"van","lastName":"Schaik","suffix":""},{"id":636023985,"identity":"f9774781-bc59-4b2a-bbce-5d72053f40e4","order_by":5,"name":"Fitriah Basalama","email":"","orcid":"","institution":"Nasional University","correspondingAuthor":false,"prefix":"","firstName":"Fitriah","middleName":"","lastName":"Basalama","suffix":""},{"id":636023995,"identity":"3749dbb7-0918-4d85-9bd5-2b8b7a28c319","order_by":6,"name":"Sri Suci Utami-Atmoko","email":"","orcid":"","institution":"Nasional University","correspondingAuthor":false,"prefix":"","firstName":"Sri","middleName":"Suci","lastName":"Utami-Atmoko","suffix":""},{"id":636024009,"identity":"ea3fe169-8d24-46e2-a7b1-b1720b1574d5","order_by":7,"name":"Caroline Schuppli","email":"","orcid":"","institution":"Max Planck Institute of Animal Behavior","correspondingAuthor":false,"prefix":"","firstName":"Caroline","middleName":"","lastName":"Schuppli","suffix":""}],"badges":[],"createdAt":"2026-04-30 09:24:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9574845/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9574845/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109093787,"identity":"a7c4bccd-9c3c-43e0-8816-bea736df662d","added_by":"auto","created_at":"2026-05-12 13:48:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":300994,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eConceptual overview of an orangutan’s daily movement and the analytical framework we used to analyse the effects of associations.\u003c/strong\u003e\u003c/em\u003e\u003cem\u003eThe figure visualises an orangutan’s daily movement path with an associate. Output metrics include daily path length (DPL), sinuosity, number of feeding hotspots visited, and time spent within a hotspot. The three-tiered analysis structure is shown whereby UF=Unflanged males, F=Flanged males, M=Mothers, and II=Independent immatures.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/51cb9258befafcba65e34681.png"},{"id":109093639,"identity":"8a488564-52eb-4784-a205-184f81aaa97a","added_by":"auto","created_at":"2026-05-12 13:47:48","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":258386,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eEffects of associations on different spatial metrics of Sumatran orangutans at the population level.\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e \u003cbr\u003e\nPanels show the relationship between the percentage of time spent in association per day and (a) daily path length, (b) daily path sinuosity, (c) number of feeding hotspots visited per day, and (d) time spent in a feeding hotspot. A value of 0% time in association represents days when the focal individual was alone. The black line represents the population-level average, while coloured lines denote individual age-sex classes. Lines are derived from model-estimated values with all predictors, except time in association, held at their mean (estimated using the emmeans() function in R), and shaded ribbons indicate 95% confidence intervals. Asterix represents significant effect of % Time in association\u003c/em\u003e \u003cem\u003e(p \u0026lt; 0.05), n.s= non-significant.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/5265966eab12d144f869f1c0.png"},{"id":109093743,"identity":"6f6083bd-0979-4e9d-9bc4-a666f35454a6","added_by":"auto","created_at":"2026-05-12 13:48:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":251255,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eEffects of associations on different spatial metrics of Sumatran orangutans, at the within-class level.\u003cbr\u003e\n \u003c/strong\u003e\u003c/em\u003e\u003cem\u003ePanels show the relationship between the percentage of time spent in association per day and (a) daily path length, (b) daily path sinuosity, (c) number of feeding hotspots visited per day, and (d) time spent in a feeding hotspot. A value of 0% time in association represents days when the focal individual was alone. Coloured lines represent each age-sex class, with separate slopes for each. Asterix represents a significant effect of % Time in association (p \u0026lt; 0.05), coloured per age-sex class. Lines are derived from model-estimated values with all predictors, except time in association, held at their mean (estimated using the emmeans() function in R), and shaded ribbons indicate 95% confidence intervals.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/502963cfe68f4ca78dceda22.png"},{"id":109093741,"identity":"004ec3ad-ed00-4952-b975-38de44191cf7","added_by":"auto","created_at":"2026-05-12 13:48:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":447951,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eDyadic spatial metrics by focal and associate age-sex class. \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eEach row represents a focal age-sex class, and each column represents either no associate (alone) or the age-sex class of the associate. Within each cell, four stacked tiles show the metrics: daily path length (DPL), sinuosity, number of hotspots visited per day (No. of HS), and time spent in a hotspot (Time in HS). Tile colour indicates the relative observed value of each metric across dyads, from green (lowest) to orange (highest), with missing values shown in light grey. Black boxes depict significant results. n = sample size per metric.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/f4909e9345e561d3f485c8e7.png"},{"id":109093809,"identity":"5a75df1f-69f5-4a54-837d-5364fc60c48b","added_by":"auto","created_at":"2026-05-12 13:48:31","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":288555,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eActivity budgets during associations with different associate classes compared to solitary periods, across focal–associate dyads.\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Each cell in the 4 × 4 matrix represents a focal–associate dyad and shows the activity budget of the focal individual. Bars indicate the percentage of time spent in each activity: feeding (F), moving (M), resting (R), nesting (N), social (S), and (O) other, per active period of a full-day observation. n=total hours of observation per dyad.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/801723e4558f4035fdd54f13.png"},{"id":109093814,"identity":"6002f2f7-6589-4abc-a7c9-6d51a481ec0b","added_by":"auto","created_at":"2026-05-12 13:48:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":139724,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eMovement order across focal–associate dyads.\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Each cell in the 4 × 4 matrix represents a focal–associate dyad and shows lead–follow movement dynamics. Stacked bars indicate the proportion of time the focal individual leads or follows movement bouts with the associate, per active period of a full-day observation. The dotted line at 50% indicates equal lead–follow proportions. n=number of observation days per dyad.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/fdbb848baf412c6c590c2e1d.png"},{"id":109204505,"identity":"8db625af-1989-4881-88fe-c98390be4b20","added_by":"auto","created_at":"2026-05-13 15:00:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1756808,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/f8455a32-e14f-4a74-a949-ba7df1f74d7f.pdf"},{"id":109093744,"identity":"dc9c119d-6eb6-440f-bcea-1df492e03cb0","added_by":"auto","created_at":"2026-05-12 13:48:11","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":92600,"visible":true,"origin":"","legend":"","description":"","filename":"ADDITIONALINFORMATION.docx","url":"https://assets-eu.researchsquare.com/files/rs-9574845/v1/50681733b7f4ede953b0b8cb.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"The immediate social environment dynamically shapes movement and foraging in wild Sumatran Orangutans (Pongo abelii)","fulltext":[{"header":"BACKGROUND","content":"\u003cp\u003eAnimal movement is shaped by an interplay of social and ecological factors, as well as individual- and group-level characteristics [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Movement ecology seeks to understand how these interacting factors generate patterns of movement across space and time that represent evolved adaptive responses [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Among these factors, sociality plays a central role: at the species level, it can facilitate or constrain individuals\u0026rsquo; spatial decisions, while within species the immediate social environment (e.g., the duration and composition of social associations) may both drive movement and emerge as a consequence of individuals\u0026rsquo; movement trajectories as they balance experienced costs and benefits [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The reciprocal relationship between the immediate social environment and movement remains poorly understood, largely owing to the complexities of social contexts that may influence individuals differently. Moreover, most movement ecology research has focused on species that are either strictly group-living or strictly solitary.\u003c/p\u003e \u003cp\u003eOrangutans represent a particularly informative system for disentangling the interplay between the immediate social environment and movement because of their flexible and context dependent sociality. Orangutans are unique among great apes in exhibiting characteristically low and dynamic tendencies to associate with conspecifics, typically described as a semi-solitary fission-fusion dynamic [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. This social system has been attributed to a combination of high energetic needs and predominantly frugivorous diet [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], which together impose a high caloric need in a habitat characterised by temporally fluctuating and spatially patchy food resources [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Despite being less gregarious than African great apes [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], orangutans do nonetheless associate more frequently than expected by chance [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], suggesting that social factors play a meaningful role in shaping their spatial ecology.\u003c/p\u003e \u003cp\u003eOrangutan associations may be passive in nature with no direct social interactions, commonly observed at foraging sites [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], or active involving coordinated movement and social attraction [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. They vary in size (i.e., the number of individuals involved) and composition (i.e., the identities of those individuals) and range from brief encounters lasting only minutes, to stable associations persisting over multiple consecutive days [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Association frequencies and sizes systematically vary across populations [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], age-sex classes [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], reproductive state [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], and habitat productivity [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], likely reflecting a dynamic balance between ecological and social costs and benefits.\u003c/p\u003e \u003cp\u003eOrangutans are subject to pronounced energetic constraints arising from the combination of their relatively large brains, large body size, energetically costly arboreal locomotion [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], and reside in low-food-density habitats that limit energy acquisition. Together, these factors place individuals under persistent energetic pressure, requiring careful trade-offs in how energy is allocated, particularly with respect to movement. Given that locomotion in orangutans is already energetically demanding, deviations from energetically efficient movement due to the presence of conspecifics likely generates costs [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] that must be offset by social benefits [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Within this context, associations can provide important social benefits, such as facilitating mating [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], enabling social learning [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], and providing play opportunities for immatures [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. However, associations can also impose costs, such as increased feeding competition [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], forced copulations [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], and potential infanticide risks [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Previous studies further suggest that association size increases an orangutan\u0026rsquo;s travel distance [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], though these studies acknowledge that individuals may differ in their intrinsic costs, such as direct locomotor costs and nutritional needs [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Conversely, avoiding associations with conspecifics may alleviate costs, though also reduce beneficial opportunities. All in all, the infrequency and conditional nature of orangutan associations and social interactions seem to reflect a trade-off between ecological constraints, energetic expenditure, and the potential advantages of sociality.\u003c/p\u003e \u003cp\u003eThe aforementioned costs and benefits of associations are predicted to shape movement decisions by influencing when orangutans tolerate or seek proximity to others versus when they prioritize being on their own and avoid associations. Each age-sex class of orangutan likely experiences a different balance of these costs and benefits.\u003c/p\u003e \u003cp\u003eOestrus females without dependent offspring actively seek mates, with associations primarily occurring for mating opportunities, however this can expose them to increased feeding competition, and also harassment from coercive mating attempts [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Mothers, in contrast, maintain prolonged associations to their dependent offspring [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], and seemingly adjust movement to reduce risk of harassment to the infant [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], prioritising offspring safety [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] over social opportunities. Flanged males, with their larger body size and secondary sexual characteristics, can monopolise access to food resources and females, influencing the movement of others [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], such as attracting females [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], and displacing other males [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. However, because of their large body size, they face more pronounced energetic costs [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], which may limit their travel [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Unflanged males, on the other hand, being smaller, have lower energy demands, allowing them to allocate more energy toward searching for females.\u003c/p\u003e \u003cp\u003eAdult females and flanged males are often resident individuals, therefore likely benefit from their greater knowledge and familiarity of the spatial distribution of resources, and social dynamics. Unflanged males, are more likely to be new to an area because of recent dispersal from their natal range leading to reduced spatial knowledge. Unflanged males are thus predicted to benefit from associating with more familiar individuals to acquire information on resource locations and social dynamics [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], although this entails risks such as displacement by dominant males and increased competition. Immature, and therefore likely more na\u0026iuml;ve, individuals are expected to benefit from associations by gaining social learning opportunities [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], important for the development of ecological competence [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. However, they may face increased energetic costs associated with the increased exploratory behaviour, and likelihood of displacement by residents [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAcross all classes, these trade-offs are likely to be context-dependent, with greater social tolerance at high-value (high abundance) feeding sites, whereby feeding competition and energetic costs are balanced by nutritional gains and temporary social advantages [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eStudying spatial metrics offers a powerful tool for examining the costs and benefits of social associations. Previous research on primate movement ecology has demonstrated the influence of social factors on travel speed [\u003cspan additionalcitationids=\"CR42\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], route choice [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], foraging patch visitation [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], and resource competition [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. However, these studies have typically focused on relatively broad social influences, such as group size, group cohesion and collective movement of group living species. Research on orangutan movement in particular has primarily focussed on individual-level spatial metrics, such as home ranges [\u003cspan additionalcitationids=\"CR48 CR49 CR50 CR51\" citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], and daily path lengths [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e], treating individuals as solitary units, rather than temporally associating conspecifics and neighbours. As a result, few empirical studies have quantified how associate identity shapes spatial metrics in semi-solitary species such as orangutans, meaning the social drivers of these unique and ephemeral interactions are therefore often overlooked.\u003c/p\u003e \u003cp\u003eIn this study, we address this knowledge gap by investigating how the presence of different age-sex classes of conspecifics, and the time spent with them, shapes movement patterns and visitation of high value food sites of wild Sumatran orangutans (\u003cem\u003ePongo abelii\u003c/em\u003e). Specifically, we quantify spatial metrics - measurable properties of how individuals move through and use space, including the length and shape of daily travel paths and the use of high-value foraging locations. We then examine how the presence of mothers, independent immatures, flanged males, and unflanged males influences these spatial metrics. By integrating fine-scale movement data, with simultaneous behavioural observations, we aim to identify how the immediate social environment modulates movement behaviour. In doing so, we provide new insight into the costs and benefits of sociability.\u003c/p\u003e \u003cp\u003eBased on the age-sex class specific costs and benefits of associations outlined above, we hypothesize that associations will differentially shape orangutan movement behaviour depending on the specific immediate social environment. As a result, we predict that both daily path length and path shape will vary systematically across age-sex classes and will shift as a function of time spent in association.\u003c/p\u003e \u003cp\u003eSpecifically, we predict that increased time in association will generally to lead to longer and more tortuous travel paths overall due to coordination demands and social interactions, whereas more solitary conditions should favour more direct and energy-efficient movement patterns. In particular, we predict that unflanged males increase path length and path sinuosity when in longer associations, reflecting mate-searching behaviour and limited spatial knowledge, whereas flanged males should show weaker social effects due to their social dominance and more pronounced energetic constraints. We further predict that mothers will reduce path length and adopt more direct (less sinuous) travel when associating with potentially risky partners such as adult males, reflecting efforts to balance infant protection, foraging efficiency, and avoidance of sexual coercion. Immatures should show reduced path length and increased linearity when associating with more spatially knowledgeable individuals.\u003c/p\u003e \u003cp\u003eWe further expect that associations alter visitation of high value food hotspots. In particular, we predict that increased time spent with others increases the number of foraging hotspots visited due to scramble competition and the need to seek alternative resources, but reduce residence time within a hotspot due to resource depletion.\u003c/p\u003e \u003cp\u003eFinally, we expect these effects to be dyad-specific at the age-sex class level, with associations involving competitors increasing travel distance and reducing food resource residence time, and associations with potential mates, more tolerant or knowledgeable individuals producing more linear travel and shared space use.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eData collection\u003c/h2\u003e\n \u003cp\u003eBetween 2007 and 2023, we conducted focal follows on wild Sumatran orangutans (\u003cem\u003ePongo abelii\u003c/em\u003e) at the Suaq Balimbing field site within the Gunung Leuser National Park, in South Aceh, Indonesia (97.431\u0026deg;E, 3.050\u0026deg;N). We categorised individuals into four age-sex classes; unflanged males (adult males exhibiting arrested development), flanged males (adult males with secondary sexual characteristics such as cheek flanges), mothers (adult females with dependent immatures), and independent immatures (who range independently from their mother). We excluded unidentified individuals, and adult females of reproductive age without offspring, due to the brief duration of this reproductive state and insufficient sample size.\u003c/p\u003e\n \u003cp\u003eWe located focal individuals by systematically traversing predefined transects within the study area, while actively surveying for recent indicators of orangutan presence (e.g., feeding traces, nests), and auditory cues such as vocalizations or canopy movement. We recorded behavioural data at 2-minute intervals using standardised behavioural ethograms [\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e], and we logged corresponding GPS locations at 10-minute intervals, using handheld GPS devices.\u003c/p\u003e\n \u003cp\u003eBehavioural data were collected from 110 individuals, including 39 unflanged males, 27 flanged males, 30 independent immatures, and 22 mothers. Of these, 72 individuals also had corresponding GPS data, comprising 20 unflanged males, 18 flanged males, 22 independent immatures, and 16 mothers. Over the course of the study, eight individuals were observed to transition between age-sex classes.\u003c/p\u003e\n \u003cp\u003eWe quantified movement using the following metrics:\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e1. Daily Path Length (DPL)\u003c/strong\u003e:\u003c/p\u003e\n \u003cp\u003eWe estimated daily path lengths using the continuous-time speed and distance (CTSD) framework [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e] in the \u003cem\u003ectmm\u003c/em\u003e R package [\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e]. Unlike conventional approaches that sum straight-line distances between successive GPS fixes, CTSD fits a continuous-time movement model to estimate mean speed, which is scaled by the daily observation duration to obtain distance travelled. This approach is robust to variation in sampling rate and path tortuosity [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e]. To reduce inflation from GPS error, we incorporated an error model with a weakly informative prior on the root mean square (RMS) user equivalent range error (UERE) centred at 15 meters (95% credible interval: ~2\u0026ndash;29 m), allowing error variance to be estimated jointly with movement parameters [\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e]. For each follow-day, the best-supported model was selected using AIC (\u003cem\u003ectmm.select\u003c/em\u003e), and daily path length was calculated as mean speed multiplied by sampling duration.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e2. Sinuosity\u003c/strong\u003e:\u003c/p\u003e\n \u003cp\u003eSinuosity is a measure of path tortuosity derived from the directional persistence and step length variation of the trajectory [\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e], where higher values indicate increasingly tortuous movement. Values were calculated using the \u003cem\u003etrj_sinuosity2\u003c/em\u003e function in the \u0026lsquo;trajR\u0026rsquo; package [\u003cspan class=\"CitationRef\"\u003e58\u003c/span\u003e].\u003c/p\u003e\n \u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equa\" class=\"mathdisplay\"\u003e$$\\:Sinuosity=2\\:[p\\left(\\frac{1+c}{1-c}\\right)+{b}^{2}){]}^{-0.5}$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere \u003cem\u003ep\u003c/em\u003e is the mean step length, \u003cem\u003ec\u003c/em\u003e is the mean cosine of turning angles, and \u003cem\u003eb\u003c/em\u003e is the coefficient of variation of the step length [\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e]. This method provides a corrected sinuosity index that generalizes the original formulation by Bovet \u0026amp; Benhamou (1988) [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e] to accommodate a wider range of turning angle distributions and variable step lengths.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e3. Number of feeding hotspots visited per day.\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e4. Time (minutes) spent in a feeding hotspot.\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eWe defined feeding hotspots as individual trees or small clusters of trees (within a 15 m crown radius) where the focal individual remained feeding continuously for more than 30 minutes. The distribution of feeding bout durations was strongly right-skewed, with a mean of 22 minutes and a modal duration of 9 minutes, revealing two distinct behavioural modes; brief sampling often whilst travelling, and prolonged feeding. Based on this distribution, we applied a conservative threshold of 30 minutes to define a feeding hotspot, as extended residence time likely reflects access to a particularly favourable food source of high abundance, when time spent feeding is used as a proxy for item value. 20.1% of feeding bouts lasted longer than 30 minutes.\u003c/p\u003e\n \u003cp\u003eWe measured total daily rainfall in millimetres, using a graduated measuring cylinder at a consistent open location at the research station, recorded at the same time each evening, representing rainfall during the day. We quantified fruit availability through monthly phenology surveys identifying fruit baring trees, performed at predefined transects spanning north to south and west to east throughout the study site, encompassing approximately 1000 trees with a diameter at breast height of \u0026gt;\u0026thinsp;20 cm. We calculated the proportion of fruiting trees and averaged this value to provide a monthly site-wide index of fruit availability.\u003c/p\u003e\n \u003cp\u003eWe analysed DPL, sinuosity and number of feeding hotspots per day using full-day focal follows, from departure from the sleeping nest to the construction of a new nest in the evening (nest-to-nest). For analyses of time spent in each hotspot, we also included shorter observation days to increase sample size, as these still captured complete feeding bouts within hotspots. For analyses of path length and sinuosity, we included only focal follows in which GPS data were available for at least 75% of the total active period length, to ensure paths were sufficiently complete and not biased by large temporal gaps.\u003c/p\u003e\n \u003cp\u003eFor each observation day, we calculated the total number of GPS waypoints recorded at 10-minute intervals as an index of sampling density, and included this variable as a control in analyses of sinuosity to account for variation in track resolution. Because sinuosity metrics depend on sampling density, we expected greater number of waypoints to inflate estimated sinuosity, as additional points capture more small-scale turns and deviations along the path. Because we expected longer active periods to correspond to greater hotspot use, reflecting increased opportunity for feeding during extended observations, we controlled for the active period duration (hours) in the analyses on hotspot usage. Path length estimates from CTMMs already account for sampling density.\u003c/p\u003e\n \u003cp\u003eFor each observation day, and during times spent in a feeding hotspot, we systematically recorded the presence or absence of associates from each of the four age-sex classes, along with percentage of time spent in association, thereby capturing the immediate social environment defined as the duration and composition of social associations. We considered associates present when they were located within 50m of the focal individual, a range that permits visual contact despite dense foliage. Given the potential for multiple associate classes to be present at the same time, we checked for multicollinearity among predictors. Model diagnostics indicated low variance inflation factors (VIFs), suggesting that the effects of different associate classes could be distinguished and were not strongly correlated.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eAnalyses\u003c/h3\u003e\n\u003cp\u003eWe quantified movement behaviour using four complementary metrics, each capturing a different aspect of spatial ecology: 1) daily path length (DPL) as a proxy for overall energetic investment in daily movement effort, 2) path sinuosity as a measure of movement efficiency, indicating whether travel was goal-directed or exploratory, 3) the number of feeding hotspots as a measure of key resource identification and utilisation, providing insights into spatial knowledge and potential cognitive maps, and 4) time spent in the feeding hotspot to assess resource exploitation and displacement from the hotspot. Together, these metrics link energy expenditure with spatial decision-making and resource use strategies.\u003c/p\u003e\n\u003cp\u003eWe implemented a three-tiered analytical framework to examine movement patterns at three different scales, considering focal age-sex class, immediate social environment and ecological factors (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). We first analysed differences in spatial metrics across all focal age-sex classes (Population-level), to evaluate overall population-level effects of age-sex class and contextual variables. Secondly (Within-class level), we ran separate models for each focal age-sex class to capture within-class variation. This approach acknowledges that behavioural responses may not be uniform across age-sex classes, and it provides class-specific estimates while retaining the same set of predictors used in the population level analyses. Third, at a dyadic level, we evaluated how the presence of associates from each age-sex class influenced the movement of each focal (Dyadic-level). For population and within-class levels we included percentage of the day spent in association as a predictor. For the dyadic level analyses we used presence and absence rather than duration as this approach was more robust given limited sample sizes of some rare dyads (\u003cem\u003eAdditional table 1\u003c/em\u003e). This approach is based on the assumption that mere presence of the associate can alter movement, regardless of association duration. Population level analyses involved the largest sample sizes and thus provided more robust population-level estimates. Building on this, within-class analyses allowed social and ecological predictors to have class-specific effects and capturing heterogeneity in behavioural responses, and the dyadic level analyses added critical understanding of dyad-specific variation, helping to explain the patterns detected at the prior levels.\u003c/p\u003e\n\u003cp\u003eFull models were fitted including the factors of age-sex class, percentage of time in association, or associate presence, as predictors, in addition to control variables: fruit availability, rainfall, and, depending on the response variable, number of GPS waypoints, or active period duration. Random intercepts for focal ID accounted for repeated measures of individuals, and follow ID for multiple measures of hotspots per day.\u003c/p\u003e\n\u003cp\u003eWe used mixed effect models to account for the non-independence of repeated measures (i.e., multiple observations per individual and multiple daily records within individuals). We used linear mixed models (LMMs; lmer) for the response variables DPL, Sinuosity, and log-transformed Time spent in a hotspot as they were continuous and approximately normally distributed. For the number of hotspots visited per day (as a count variable), we used generalised linear mixed models (GLMMs; glmmTMB) with a Conway-Maxwell Poisson distribution. We used packages \u0026lsquo;lme4\u0026rsquo; [\u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e] to fit LMMs, and \u0026lsquo;glmmTMB\u0026rsquo; [\u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e] to fit GLMM models, with appropriate diagnostic checks performed to verify model assumptions. Detailed model structures and sample sizes are provided in Additional table 1.\u003c/p\u003e\n\u003cp\u003eAll analyses were conducted in R [\u003cspan class=\"CitationRef\"\u003e62\u003c/span\u003e]. We used Likelihood Ratio Tests (LRTs) via the \u003cem\u003eanova\u003c/em\u003e function to compare full models (containing all predictors and random intercepts) to null models (containing only random intercepts). We assessed significance of fixed effects using Type III Wald \u0026chi;\u0026sup2; tests, and we conducted Tukey-adjusted post-hoc pairwise comparisons [\u003cspan class=\"CitationRef\"\u003e63\u003c/span\u003e] to evaluate differences among age-sex classes.\u003c/p\u003e\n\u003cp\u003eTo complement quantitative analyses of movement and association patterns, we also investigated behaviours occurring during the recorded associations. We calculated activity budgets by summarising the percentage of time the focal spent feeding, resting, moving, nesting, socialising, and engaging in other behaviours, when with an associate, per follow, and then averaged per age-sex class dyad. We identified which individual initiated and which followed in each movement bout to distinguish individuals seeking social opportunities from those serving as the target. For each follow, we calculated the daily proportion of bouts in which the focal led or followed, then averaged these values across age-sex class dyads to ensure equal weighting. By linking movement and foraging behaviour to its social context, we provide a rare test of how the presence and class of associates modulates animal decision-making.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003ePopulation-level effects of associations and age-sex class on movement and foraging patterns\u003c/h2\u003e \u003cp\u003eOn average, orangutans at Suaq Balimbing were alone 53.6% of the time, and with 1 other individual (excluding dependent immatures) 26.9% of the time, and with 2 or more individuals 19.6% of the time. In particular, independent immatures were the most social class, being with at least one associate 57.9% of the time, followed by unflanged males (50.0%) and mothers (46.1%), whereas flanged males were with an associate only 32.7% of the time.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eDaily path length\u003c/span\u003e: Orangutans at Suaq Balimbing travelled 1130 m per day on average (\u0026plusmn;\u0026thinsp;503m SD) when alone, but the more time they spend in social associations the farther they travel each day (1201m on average when in association all day; \u0026plusmn;425m SD). A likelihood ratio test (LRT) indicated that the full model explained significantly more variation in daily path length (DPL) than the corresponding null model (χ\u0026sup2;(6)\u0026thinsp;=\u0026thinsp;18.103, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.006). Time spent in association (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.58, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.032) showed a significant positive effect on DPL (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Age-sex class also had a significant overall effect on DPL (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;8.53, p\u0026thinsp;=\u0026thinsp;0.036); however, Tukey-adjusted pairwise comparisons of estimated marginal means revealed no significant differences between specific classes (all p\u0026thinsp;\u0026gt;\u0026thinsp;0.05), suggesting that while class explains some variance in path length, no individual class differs clearly from the others. Fruit availability had a significant positive effect on DPL (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;3.88, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.048). Rainfall did not significantly affect DPL. Complete model outputs are provided in Additional table 2.\u003c/p\u003e \u003cp\u003eTo determine whether longer paths were mediated by associate presence leading to longer observational periods, we re-ran the full model on DPL, with the inclusion of active period duration as a control variable. The results revealed no significant effect of time in association in this model (Additional table 3), signifying that individuals that spend more time in association do not travel farther per unit time, but they are active for longer, which results in greater total movement distances.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSinuosity of the daily path\u003c/span\u003e: Orangutans\u0026rsquo; paths became straighter when individuals were with associates, and unflanged males in particular tended to travel in more linear trajectories than mothers. The full model explained significantly more variation in path sinuosity than the corresponding null model (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;63.538, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Model results showed a trend towards a negative effect of time spent in association on daily path sinuosity (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;3.76, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.053) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The overall effect of age-sex class on trajectory sinuosity was significant (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;18.44, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Post-hoc pairwise comparisons showed that mothers had significantly higher sinuosity than unflanged males (mean difference\u0026thinsp;=\u0026thinsp;0.039, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), whereas all other pairwise contrasts were not significant. Fruit availability and rainfall did not significantly affect daily path sinuosity. Daily path sinuosity increased with the number of waypoints recorded per day (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;43.80, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Additional table 4).\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eNumber of feeding hotspots visited per day\u003c/span\u003e: Orangutans generally focused on a few key feeding sites per day, which varies per age-sex class (on average, the mean observed number of hotspots visited per day was 5.4 for flanged males, 4.8 for mothers, 4.6 for independent immatures, and 4.4 for unflanged males), with fewer hotspots visited when in association. The full model explained significantly more variation in the number of hotspots visited per day compared to the corresponding null model (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;59.957, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001). There was a significant negative effect of time spent in association on the number of feeding hotspots visited per day (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;25.79, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Age-sex class had a significant overall effect on the number of hotspots visited per day (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;15.77, p\u0026thinsp;=\u0026thinsp;0.001). Post-hoc comparisons indicated that flanged males visited more hotspots than independent immatures (rate ratio\u0026thinsp;=\u0026thinsp;1.18, p\u0026thinsp;=\u0026thinsp;0.003), mothers (rate ratio\u0026thinsp;=\u0026thinsp;1.15, p\u0026thinsp;=\u0026thinsp;0.021), and unflanged males (rate ratio\u0026thinsp;=\u0026thinsp;1.20, p\u0026thinsp;=\u0026thinsp;0.014), while all other pairwise contrasts were not significant. The number of hotspots visited per day increased significantly with active period duration (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;21.74, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Fruit availability and rainfall did not significantly affect the number of hotspots visited per day.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eTime spent in feeding a hotspot\u003c/span\u003e: Orangutans spent less time at a feeding hotspot when associating with others, and the extent of this varied per age-sex class. The observed mean time spent in a hotspot was 57 minutes for flanged males, 54 minutes for unflanged males, 52 minutes for mothers, and 51 minutes for independent immatures. The full model explained significantly more variation in time spent in a feeding hotspot than the corresponding null model (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;34.49, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Model results showed a significant negative effect of time spent in association on the time spent in a hotspot (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;13.31, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Age-sex class had a significant overall effect on time spent in a hotspot (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;15.12, p\u0026thinsp;=\u0026thinsp;0.002). Post-hoc comparisons of estimated marginal means (back-transformed from the log scale) indicated that flanged males spent significantly longer (~\u0026thinsp;6\u0026ndash;8%) in a hotspot than independent immatures (ratio\u0026thinsp;=\u0026thinsp;1.08, p\u0026thinsp;=\u0026thinsp;0.002) and mothers (ratio\u0026thinsp;=\u0026thinsp;1.07, p\u0026thinsp;=\u0026thinsp;0.009), while all other pairwise contrasts were not significant. Active period duration, fruit availability, and rainfall did not significantly affect time in a hotspot.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003ePanels show the relationship between the percentage of time spent in association per day and (a) daily path length, (b) daily path sinuosity, (c) number of feeding hotspots visited per day, and (d) time spent in a feeding hotspot. A value of 0% time in association represents days when the focal individual was alone. The black line represents the population-level average, while coloured lines denote individual age-sex classes. Lines are derived from model-estimated values with all predictors, except time in association, held at their mean (estimated using the emmeans() function in R), and shaded ribbons indicate 95% confidence intervals. Asterix represents significant effect of % Time in association (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), n.s\u0026thinsp;=\u0026thinsp;non-significant.\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eWithin-class effects of associations on movement and foraging patterns\u003c/h3\u003e\n\u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eDaily path length\u003c/span\u003e: Within classes, individuals did not consistently increase their daily travel distance when spending more time in association (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). For unflanged males, the full model on DPL did not explain significantly more variation than the respective null model (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;7.689, p\u0026thinsp;=\u0026thinsp;0.053), although there was a trend. The full model revealed a positive effect of time spent in association on daily path length (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.951, p\u0026thinsp;=\u0026thinsp;0.026). For flanged males (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;7.123, p\u0026thinsp;=\u0026thinsp;0.068), mothers (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;1.095, p\u0026thinsp;=\u0026thinsp;0.778), and immatures (χ\u0026sup2;(3)\u0026thinsp;=\u0026thinsp;0.623, p\u0026thinsp;=\u0026thinsp;0.890), the full models did not explain more variance in daily path length than the respective null models. Fruit availability and rainfall had no significant effects on DPL in any class (all p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSinuosity of the daily path\u003c/span\u003e: Within age-sex classes, path shapes were generally unaffected by time spent in association (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The full model explained significantly more variance in daily path sinuosity than their corresponding null model for unflanged males (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;14.297, p\u0026thinsp;=\u0026thinsp;0.006), flanged males (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;18.161, p\u0026thinsp;=\u0026thinsp;0.001), and mothers (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;28.73, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), but not for independent immatures (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;2.158, p\u0026thinsp;=\u0026thinsp;0.707). Time spent in association did not significantly affect sinuosity in any class, however, across classes, the total number of waypoints per path consistently positively affected sinuosity (unflanged males: χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;7.74, p\u0026thinsp;=\u0026thinsp;0.005; flanged males: χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;15.19, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001; mothers: χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;25.36, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Rainfall reduced path sinuosity for unflanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.514, p\u0026thinsp;=\u0026thinsp;0.034). Fruit availability had a positive effect on sinuosity for flanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;6.059, p\u0026thinsp;=\u0026thinsp;0.014).\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eNumber of feeding hotspots visited per day\u003c/span\u003e: Flanged males and mothers visited fewer feeding hotspots when associating with others, while unflanged males and immatures showed no clear social effect (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The full model explained significantly more variance in the number of feeding hotspots visited per day than the corresponding null model for flanged males (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;18.04, p\u0026thinsp;=\u0026thinsp;0.001) and mothers (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;19.76, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), but not for unflanged males (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;5.15, p\u0026thinsp;=\u0026thinsp;0.272) or immatures (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;8.56, p\u0026thinsp;=\u0026thinsp;0.073). For both flanged males and mothers, time spent in association negatively affected the number of hotspots (flanged males: χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;9.67, p\u0026thinsp;=\u0026thinsp;0.002; mothers: χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;9.67, p\u0026thinsp;=\u0026thinsp;0.002). Active period duration had a positive effect on the number of hotspots for both flanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;9.97, p\u0026thinsp;=\u0026thinsp;0.002) and mothers (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;11.09, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Fruit availability and rainfall had no significant effect on the number of hotspots visited for any class.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eTime spent in feeding a hotspot\u003c/span\u003e: Flanged males spent less time at a feeding hotspot when associating with others, whereas unflanged males, immatures and mothers\u0026rsquo; hotspot visitation duration was unaffected by social context (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The full model explained significantly more variance in the time spent in a feeding hotspot than the corresponding null model for flanged males (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;13.81, p\u0026thinsp;=\u0026thinsp;0.008) and marginally so for independent immatures (χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;9.46, p\u0026thinsp;=\u0026thinsp;0.051). For unflanged males and mothers, the full model did not explain significantly more variance than the null model (unflanged: χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;4.7473 p\u0026thinsp;=\u0026thinsp;0.691; mothers: χ\u0026sup2;(4)\u0026thinsp;=\u0026thinsp;2.90, p\u0026thinsp;=\u0026thinsp;0.575). Time spent in association at the hotspot negatively affected hotspot duration for flanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;9.16, p\u0026thinsp;=\u0026thinsp;0.002) and immatures (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;8.02, p\u0026thinsp;=\u0026thinsp;0.005). Active period duration, fruit availability, and rainfall had no significant effects for any class.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003ePanels show the relationship between the percentage of time spent in association per day and (a) daily path length, (b) daily path sinuosity, (c) number of feeding hotspots visited per day, and (d) time spent in a feeding hotspot. A value of 0% time in association represents days when the focal individual was alone. Coloured lines represent each age-sex class, with separate slopes for each. Asterix represents a significant effect of % Time in association (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), coloured per age-sex class. Lines are derived from model-estimated values with all predictors, except time in association, held at their mean (estimated using the emmeans() function in R), and shaded ribbons indicate 95% confidence intervals.\u003c/em\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDyadic effects of focal\u0026ndash;associate class combination on movement and foraging patterns\u003c/h2\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eDaily Path Length\u003c/span\u003e: Mothers adjusted their daily travel distances depending on which associates were present, whereas immatures, unflanged and flanged males\u0026rsquo; distances were unaffected by different classes of associates. The full models explained significantly more variance in DPL than the corresponding null models for mothers (χ\u0026sup2;(6)\u0026thinsp;=\u0026thinsp;14.672, p\u0026thinsp;=\u0026thinsp;0.023), but not for immatures (χ\u0026sup2;(6)\u0026thinsp;=\u0026thinsp;3.655, p\u0026thinsp;=\u0026thinsp;0.723), unflanged males (χ\u0026sup2;(6)\u0026thinsp;=\u0026thinsp;5.560, p\u0026thinsp;=\u0026thinsp;0.474) or flanged males (χ\u0026sup2;(5)\u0026thinsp;=\u0026thinsp;3.424, p\u0026thinsp;=\u0026thinsp;0.635). For Mothers, the presence of flanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;7.733, p\u0026thinsp;=\u0026thinsp;0.005) affected DPL, while the presence of other classes did not (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Fruit availability and rainfall had no significant effect.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSinuosity of the daily path\u003c/span\u003e: At the dyadic level, different classes of association partners had generally limited effects on path sinuosity, although unflanged males\u0026rsquo; trajectories became more sinuous in the presence of immatures, and mothers\u0026rsquo; trajectories became less sinuous in the presence of flanged males. The full models explained significantly more variance in path sinuosity compared to the null models for unflanged males (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;17.06 p\u0026thinsp;=\u0026thinsp;0.017), flanged males (χ\u0026sup2;(6)\u0026thinsp;=\u0026thinsp;13.93, p\u0026thinsp;=\u0026thinsp;0.030), and mothers (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;9.27, p\u0026thinsp;=\u0026thinsp;0.234), but not for immatures (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;6.30, p\u0026thinsp;=\u0026thinsp;0.505). For unflanged males, path sinuosity was positively affected by number of waypoints (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;8.19, p\u0026thinsp;=\u0026thinsp;0.004), and rainfall (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.38, p\u0026thinsp;=\u0026thinsp;0.036). For flanged males, path sinuosity was positively affected by number of waypoints (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;8.39, p\u0026thinsp;=\u0026thinsp;0.004). For mothers, path sinuosity was positively affected by flanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.01, p\u0026thinsp;=\u0026thinsp;0.045), fruit availability (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.33, p\u0026thinsp;=\u0026thinsp;0.038), and number of waypoints (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;33.84, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eNumber of feeding hotspots visited per day\u003c/span\u003e: Mothers visited fewer feeding hotspots when male associates were present, whereas flanged and unflanged males and immatures\u0026rsquo; hotspot use was largely unaffected by different classes of associates. For mothers, the full model explained significantly more variance in the number of feeding hotspots visited per day than corresponding the null model (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;27.35, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Mothers visited fewer hotspots when unflanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;9.23, p\u0026thinsp;=\u0026thinsp;0.002) or flanged males (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.06, p\u0026thinsp;=\u0026thinsp;0.044) were present (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), while follows of longer duration were associated with a greater number of hotspots visited (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;15.21, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Other predictors were non-significant. For unflanged males, flanged males and independent immatures, the full models did not explain significantly more variance in hotspot use than the null models.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eTime spent in a feeding hotspot\u003c/span\u003e: Mothers adjusted how long they stayed at a feeding hotspot depending on the class of the associate, whereas hotspot durations were unaffected by the presence of different classes of associates for the other focal classes. For mothers, the full model explained significantly more variance in the time spent in a feeding hotspot than the null model (χ\u0026sup2;(7)\u0026thinsp;=\u0026thinsp;19.95, p\u0026thinsp;=\u0026thinsp;0.006). The presence of flanged males increased mothers\u0026rsquo; time in a hotspot (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;12.01, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), whereas the presence of other mothers decreased it (χ\u0026sup2;(1)\u0026thinsp;=\u0026thinsp;4.49, p\u0026thinsp;=\u0026thinsp;0.034). Other predictors, including the presence of unflanged males, immatures, fruit availability, active period duration, and rainfall, had no significant effects. All other predictors were non-significant. For unflanged and flanged males, likelihood ratio tests indicated that the full models did not explain more variance than the null.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eActivity Budget\u003c/span\u003e: The dyad-specific activity budgets revealed differences in how focal individuals allocate time across behaviours depending on their associate. Feeding was the most prevalent behaviour across all focal individuals; this pattern held true for every focal-associate dyad as well as when individuals were alone (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e\u003cem\u003e)\u003c/em\u003e. The highest proportion of time spent moving was when flanged males were in association with unflanged males (22.0%), whereas their movement was lowest (15.8%) when with other flanged males. Resting was most prominent for flanged males, peaking at 24.8% when with independent immatures, though least for independent immatures overall (14.8\u0026ndash;19.6%). Social interactions were generally rare, with independent immatures consistently allocating the least time (0.3\u0026ndash;0.7%). Notably the highest proportion of social behaviour was when flanged males associated with unflanged males (2.6%), primarily in the form of social watching and social aggression towards the associate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMovement order\u003c/span\u003e: Analysis of movement sequence behaviour revealed the proportion of times the focal followed associates or led movement bouts. Independent immatures generally led movement when paired with flanged and unflanged males, but tended to follow mothers (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Mothers led movement more often than followed regardless of associate class. Flanged males tended to follow mothers, while unflanged males tended to follow associates from all classes, except in the presence of flanged males, where proportions were more equal.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eBy integrating fine-scale movement data with detailed behavioural observations, we move beyond describing \u003cem\u003ehow\u003c/em\u003e orangutans travel, to explaining \u003cem\u003ewhy\u003c/em\u003e they make these movement decisions. This study provided a multidimensional view of how orangutans dynamically adjust movement in response to their immediate social environment and, in doing so, sheds novel light on the costs of sociality. This socially responsive movement supports predictions that this semi-solitary ape experiences measurable locomotor and foraging trade-offs when associating with conspecifics, and also that these trade-offs vary across age-sex classes.\u003c/p\u003e \u003cp\u003ePrevious research shows that orangutan associations vary across age-sex class [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], reproductive state [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], and habitat productivity [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In line with this, our analyses identified the immediate social environment as a consistent driver of movement decisions, with effects varying between focal-associate dyads.\u003c/p\u003e\n\u003ch3\u003eEffects of associations on daily path length\u003c/h3\u003e\n\u003cp\u003eWe predicted that time spent in association increases daily path length due to coordination demands and social interactions, whereas solitary conditions favour more direct and energy-efficient movement. Our results partially supported this prediction, showing that sociality imposes a measurable locomotor cost for orangutans: individuals travelled farther on days with greater social engagement (population level analyses), but this effect was not consistent across all age-sex classes and social contexts.\u003c/p\u003e \u003cp\u003eUnflanged males generally travelled the farthest, followed by immatures, flanged males, and then mothers. For unflanged males, long paths likely reflect mating strategies involving active tracking and monitoring of potential mates. Moreover, unflanged males typically have less familiarity with the area, and must therefore expand their knowledge of the distribution of resources and conspecifics, through exploration similar to immatures, after dispersing out of their natal range to avoid inbreeding [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Similarly, long paths for immatures are consistent with the exploratory ranging behaviour of dispersing immatures, who must gain spatial knowledge of resource distribution during the development of ecological competence [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e], and home range establishment [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. However, the absence of reduced travel distance during associations, even with knowledgeable residents, may indicate that immatures do not use others\u0026rsquo; spatial knowledge to optimise movement. It is also possible that the influence of associates varies across immature age and was therefore not captured in the present model. Longitudinal or cross-sectional analyses would help determine whether immatures benefit from associations at specific ages. Mothers and flanged males, who often have established stable home ranges, and are therefore more knowledgeable of resource locations, are constrained by the need to balance energy expenditure against foraging gains and thus have shorter paths overall. Mothers in particular bear the high costs of pregnancy and offspring care, whilst flanged males mostly bear the cost of large body size, therefore prioritise energy conservation.\u003c/p\u003e \u003cp\u003eImportantly, at the population level, increased daily path length reflected longer periods of activity rather than faster movement. This indicates that individuals in social contexts do not necessarily move more intensively, but instead remain active for longer periods, resulting in greater total daily travel distances. Given the high energetic costs of locomotion in orangutans, driven by their large body size and arboreal lifestyle, even modest increases in daily travel may create significant energetic costs [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDyadic analyses further highlighted that the effects of social context are partner-specific. Mothers increased their daily path length when in the presence of flanged males. Females are generally thought to preferentially associate with flanged males as mating partners, while tending to avoid unflanged males, which are more often associated with coercive mating attempts. Consequently, longer paths when with flanged males may reflect mate seeking behaviour driven by female choice. Longer movement paths away from males, prioritising infant protection, would be expected to be more pronounced in the presence of unflanged males. However, flanged males that are newly immigrated or only recently attained dominance likely have a lower probability of paternity and could therefore represent a potential threat to infants [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. This cost is further reflected in mothers leading movement bouts during their longer daily paths to avoid flanged males. Subsequently, associations with males can impose costs on females, reflecting a form of sexual conflict, with variation depending on male morph and context, aligning with published research on costs of associating with males [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. In this light, our findings suggest that mothers adjust their movement not simply in response to associate presence per se, but according to the perceived risks and benefits associated with flanged males.\u003c/p\u003e \u003cp\u003eThe absence of dyadic effects in immatures and both flanged and unflanged males may indicate that social influences on path length are only expressed during periods of coordinated travel. Across the full day, other activities such as resting, feeding, or socialising with an associate may not substantially affect overall path length or its structure.\u003c/p\u003e \u003cp\u003eMoreover, there were no data available on the presence of flanged males with other flanged males for full-day observations with sufficient GPS data, which provides some evidence for avoidance behaviour between the dominant males. Moreover, activity budget behavioural data revealed that when flanged males and unflanged males associated with other flanged males, they had the highest proportions of time spent travelling, and the greatest reduction in time spent feeding, compared to other dyads, providing further evidence for avoidance and displacement behaviour, and subsequent energetic costs.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eEffects of associations on daily path sinuosity\u003c/h2\u003e \u003cp\u003eWe predicted that increased time spent in association would increase path sinuosity due to the need to coordinate movement decisions, or avoid others. Results showed that path sinuosity appeared relatively stable across immediate social environments but differed among age-sex classes. This suggests that while social factors such as feeding competition or the opportunity to benefit from another\u0026rsquo;s spatial knowledge do not influence the directness of travel routes, energetic requirements and nutritional needs may.\u003c/p\u003e \u003cp\u003eAt the population level, mothers exhibited more sinuous paths than unflanged males, which most likely reflects contrasting ranging strategies. Mothers may adopt more sinuous movement patterns as they forage intensively within localised areas, repeatedly revisiting resource patches to meet the high energetic demands, and potential nutrient requirements of pregnancy, lactation [\u003cspan additionalcitationids=\"CR69\" citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e] and infant care, while minimising travel costs. Mothers may also deviate from spatially efficient travel paths, as they must select routes with smaller canopy gaps that allow offspring to cross [\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e], and occasionally return to retrieve them if they fall behind.\u003c/p\u003e \u003cp\u003eMore linear movement paths in unflanged males may reflect direct, goal-oriented travel toward resources or social targets, potentially increasing encounters with receptive females. Such straighter trajectories could indicate a strategy that enhances encounter rates while improving travel efficiency, thereby offsetting the energetic costs of their long daily paths. This interpretation contrasts with the expectation that unflanged males have limited spatial knowledge, instead suggesting they can navigate their environment efficiently.\u003c/p\u003e \u003cp\u003eOverall, dyadic social context had varying effects on path sinuosity. Some class-specific associations were evident (e.g., increased sinuosity in unflanged males in the presence of immatures and reduced sinuosity in mothers when accompanied by flanged males). Taken together, these results suggest that path sinuosity is primarily structured by focal age-sex class, but also the immediate social environment can shape movement patterns in specific contexts.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eEffects of associations on feeding hotspot use\u003c/h2\u003e \u003cp\u003eWe predicted that sociality would increase the number of feeding hotspots visited due to scramble competition, and reduce the time spent at each hotspot because of resource depletion. At the population level, our results showed that foraging behaviour, as measured by hotspot visitation and time spent in each hotspot, varied across immediate social environments and between age-sex classes. Contrary to our predictions, individuals visited fewer hotspots as time in association increased and also spent less time at each hotspot (population level analyses). These findings provide detailed insight into feeding competition, suggesting that individuals do not compensate for visiting fewer hotspots by prolonging their visits. Instead, sociality appears to constrain both the breadth and intensity of resource exploitation. However, this pattern may also partly reflect a methodological effect driven by patch depletion rates. When individuals are in association, increased feeding competition may lead to faster resource depletion, resulting in shorter visits that fall below the threshold required for a location to be classified as a hotspot. In contrast, when alone, individuals may exploit the same patches for longer due to lower depletion rates, increasing the likelihood that these locations are identified as hotspots. Thus, some patches with high resource potential may be underrepresented as hotspots in social contexts, potentially exemplified by our result of fewer hotspots visited and less time spent in them when in longer associations.\u003c/p\u003e \u003cp\u003eAge-sex class differences were also evident, flanged males exploited the greatest number of feeding hotspots, and also spent more time in them, than the other age-sex classes. This pattern may reflect greater local knowledge, and a strategy of exploiting and exhausting foraging resources without the added costs of searching for alternative resources, given the high energetic costs of locomotion in flanged males [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e]. The social dominance of flanged males also likely allows them to monopolise resources and therefore displace associates. However, despite exploiting hotspots the most, as the percentage of time spent in association increased, they visited fewer hotspots, and spent less time in them (within-class level analyses). Similar effects were seen for mothers, who visited fewer hotspots as association time increased, and immatures, whose time spent in a hotspot also decreased when spending longer time in associations.\u003c/p\u003e \u003cp\u003eWe found several dyad-specific trends suggesting that the class of associates may differentially influence levels of feeding competition and evidence for individuals\u0026rsquo; strategies to compensate for it (dyadic level analyses). For instance, mothers visited less hotspots when around flanged and unflanged males, but extended hotspot residence time in the presence of flanged males. This result suggests that mothers compensate for the reduced number of hotspots visited when with flanged males by exploiting them more thoroughly, consistent with energy conservation strategies. This result may also reflect increased social tolerance between females and flanged males. Females regularly actively seek the presence of flanged males [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] whereas they tend to avoid unflanged males who actively seek and often perturb them [\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e]. Orangutan mothers are known to display high levels of social tolerance to other females and immatures, especially their close relatives [\u003cspan additionalcitationids=\"CR75\" citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e]. However, the results of this current study reveal that the presence of mothers reduces time in a hotspot in other mothers. This highlights that competition and resource depletion are likely the key drivers of foraging patch exploitation, when mating benefits are absent.\u003c/p\u003e \u003cp\u003eExamining dyad-specific associations revealed that the class of social partners, rather than sociality as a whole, plays a critical role in shaping movement and foraging behaviour for some age-sex classes, particularly mothers. In contrast, adult males, particularly flanged males, showed relatively limited sensitivity to the identity of associates, suggesting greater autonomy in their movement and foraging decisions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eSocial modulation of activity budgets and movement initiation\u003c/h2\u003e \u003cp\u003eOverall, being in association did not substantially alter the pattern of activity budgets. Across all contexts, whether alone or with different classes of associates, individuals devoted the largest proportion of their time to feeding (around 50\u0026ndash;60%), followed by movement and resting. However, associations may influence the functional basis of these activities. Feeding in close proximity to associates may be particularly important for spatially na\u0026iuml;ve individuals, such as immatures and unflanged males, by facilitating the acquisition of food locating, and extractive foraging skills. Travel with partners may enhance spatial learning of resource distribution, while resting alongside associates may provide opportunities for observational social learning.\u003c/p\u003e \u003cp\u003eOverall, associations generally led to a larger proportion of the activity budget spent moving, longer total active periods, and consequently increased path length, all of which carry energetic costs. However, individuals did not appear to offset these costs by increasing energy intake by spending more time feeding. Flanged males in particular faced the greatest reduction in time spent feeding when associating with unflanged males. Instead, there was a modest increase in time allocated to resting, socialising, and other activities (such as independent exploration, and long-call vocalisations).\u003c/p\u003e \u003cp\u003eMovement bout order adds another layer of evidence to what factors underly movement decisions. Following an associate can create opportunities for social learning, particularly from more knowledgeable individuals, whereas leading the movement shows active spatial decision making. Patterns of dyadic movement order were consistent with female mate choice and the contrasting mating strategies of the two male morphs; unflanged males tended to follow mothers, and to a lesser extent immatures, consistent with their strategy of seeking mates. Females instead tended to seek out flanged males, reflecting their mating preference. Unflanged males were frequently displaced when in associations with flanged males, a pattern reflected in the proportions of movement bouts and the lack of these dyadic associations in general.\u003c/p\u003e \u003cp\u003eIndependent immatures were the most social class, with an associate more often than alone, though engaged in relatively little direct social interactions, compared to the other age-sex classes. Despite limited direct interactions, their greater level of sociality may confer indirect social benefits: by being within sight of more experienced individuals, they could gain access to information about resource locations, conspecific location, or predator avoidance without the costs of direct interaction or conflict. In this way, social association acts as a low-risk learning environment, allowing immatures to benefit from the knowledge and experience of others. They followed tolerant or knowledgeable resident individuals [\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e], especially their own mothers [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], but seemed to avoid potentially risky males, indicating selective social use of information. This combination supports published literature stating an exploratory [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e], learning oriented [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e] movement strategy. Conversely, flanged males were the least social class, though when with an associate, they did invest more time in direct social behaviour, particularly mating and observing mothers, and displaying aggression to other males. Their large body size and social dominance suggests priority access to resources and reduced need to modify travel due to associates, aligning with an energy-conserving, dominance-based movement strategy. Mothers had a more stable activity budget regardless of associate class, and they frequently led movement, likely avoiding costly associations [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. They were sensitive to associate identity, reflected with their longer daily paths, and use of fewer foraging hotspots when with flanged males, but varied time spent in a hotspot depending on associate class. Together, these patterns indicate an energetic conservation and infant protection driven strategy shaped by the demands of caregiving. Unflanged males varied in their allocation of time to social behaviours depending on the age-sex class of the associate, likely due to seeking mates and avoiding rival males. Interestingly, unflanged males and independent immature dyads devoted the highest proportion of time in association to feeding, which likely helps these classes, who have relatively limited knowledge of resource locations, share information about where to find food. Overall, these patterns suggest that associations actively structure behavioural investment and learning opportunities across age-sex classes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eEcological effects on movement and foraging behaviour\u003c/h2\u003e \u003cp\u003eInterestingly, ecological variation, specifically fruit availability, did not have a consistent influence on movement, despite the largest proportion of the active period devoted to foraging and consuming food. Only some age-sex class specific ecological effects emerged at the within-class level analyses, such as unflanged males travelling more direct under challenging environmental conditions of increased rainfall, and flanged males increasing path sinuosity to exploit higher fruit availability in the local area, consistent with more localised searching or patch use when resources are abundant. This absence of consistent effects of fruit availability may be specific to the Suaq Balimbing site, which benefits from relatively high and stable food availability, compared to other orangutan research sites. Similar observations have been reported in other studies at Suaq, such as when alternative measures of fruit availability (eFAI; which calculated the actual fruit availability experienced by the individual, rather than habitat-level availability) showed minimal effects on ranging [\u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e]. A different study on the same population found that fruit availability did not show any impact on day journey length [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], whereas another found contrasting results on male path length [\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e]. Moreover, additional studies found that fruit availability at Suaq Balimbing was not strongly linked to party size [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], insect-feeding preferences [\u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e], or social play [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], in contrast to other sites where stronger effects have been observed. Hence, the effects of fruit availability are likely to be less pronounced at Suaq than other sites.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eSeveral limitations should be considered. The number of GPS waypoints strongly influenced sinuosity, so we included it as a control covariate because it correlates with both active period duration and data resolution. While active duration limits total movement, resolution directly affects calculated metrics by capturing more fine-scale path deviations, making this control essential to distinguish biological from methodological effects. However, the nature of the effect of the number of way points on sinuosity would need to be explored in detail to assure that adding it as a linear control is the best practice. Importantly, the observed age-sex differences in movement remained robust after accounting for waypoint number, indicating that our main conclusions are driven by genuine behavioural differences rather than artefacts of active period duration or GPS sampling density.\u003c/p\u003e \u003cp\u003eSecondly, dyad-specific analyses varied in sample size, particularly for males, whereby low sample size itself provides evidence for social intolerance, but also reduced power to detect subtle social effects. The absence of significant effects in the current data set therefore does not fully rule out their presence. Conversely, because of sample size limitations, we did not control for repeated testing, for example by adjusting our significance threshold [\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e]. While it is common practice for studies with sample size limitations to not adjust significant thresholds to avoid reducing statistical power, it does inflate the risk of false positive effects. Finally, fruit availability, though a method consistent within published literature, is measured at relatively course temporal scales, which do not accurately reflect fine-scale resource depletion, or orangutans dietary preference. Future work integrating high resolution resource mapping may reveal additional ecological influences not captured in this study.\u003c/p\u003e \u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eBy using orangutans as a model system and leveraging an exceptionally detailed long-term dataset on movement and behaviour, we generated broader insights into the energetic costs of social associations, in relation to movement and foraging, and the mechanisms through which potential benefits can offset them. As semi-solitary apes that, due to their large body size and arboreal lifestyle, face pronounced energetic constraints [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e], orangutans provide a valuable framework to investigate the costs and benefits of social association [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e]. Our study concludes that Orangutan movement is best understood as demographically structured (age-sex driven) and individually expressed, yet socially shaped in many aspects. Social interactions may influence when and how far individuals travel, and how they utilize foraging hotspots, but they do not appear to strongly restructure the fine-scale geometry of daily movement paths. This study sheds novel light on the mechanisms underlying feeding competition as well as how these costs of associations are dynamically weighted by the benefits of spatial knowledge sharing, such as skill acquisition [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], enhanced discovery of resources [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], protection from harassment [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], and mating opportunities [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMore broadly, these results contribute to the growing evidence that even species traditionally characterised by their semi-solitary nature, exhibit socially responsive movement strategies, akin to those observed in more gregarious species, challenging simple dichotomies between solitary and group living species. By integrating spatial metrics with fine-scale behavioural data, such as activity budgets and order of movement bouts, we were able to move beyond describing \u003cem\u003ehow\u003c/em\u003e individuals move, to shed novel light on \u003cem\u003ewhy\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eTaken together, our study emphasises that trade-offs between costs and benefits of associations are flexible and context dependent, and should be considered central to understanding ranging behaviour. Recognising this socially mediated flexibility is particularly important for conservation, as changes in population density particularly in fragmented habitats may alter these trade-offs and, consequently, the energetic balance of individuals.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDPL\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eDaily Path Length\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eLMMs\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eLinear mixed models\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eGLMMs\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eGeneralised linear mixed models\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eLRTs\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eLikelihood ratio tests\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eHS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eHotspot\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eANOVA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eAnalysis of variance\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ei.e.\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eId est\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003en\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eNumber\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003em\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e \u003cem\u003eMeters\u003c/em\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eχ\u0026sup2;\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eChi-squared statistic\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCTSD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eContinuous-time speed and distance\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCTMM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eContinuous time movement model\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cu\u003eEthics approval and consent to participate\u003c/u\u003e: Research was conducted in compliance with relevant institutional and national guidelines, and approved by The National Research and Innovation Agency’s ethics committee (BRIN Ethical clearance Ref No.: 026/KE.02/SK/8/2022)\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eConsent for publication\u003c/u\u003e: Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAvailability of data and materials\u003c/u\u003e: The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eCompeting interests\u003c/u\u003e: The authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eFunding\u003c/u\u003e: This research was supported and funded by the Max Planck Institute of Animal Behavior (C.S., E.L.), University of Zurich (C.S.), the A.H. Schultz Foundation (C.S.), the Leakey Foundation (Primate Research Fund and project grant) (C.S.), the SUAQ Foundation (C.S.), the Volkswagen Stiftung (Freigeist fellowship to C.S.), the Stiftung für Mensch und Tier (Freiburg i.Br. to C.S.), and the International Max Planck Research School for Quantitative Behaviour, Ecology and Evolution (IMPRS-QBEE)(E.L).\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAuthors' contributions\u003c/u\u003e: E.L contributed to data collection, conducted statistical analyses, interpreted the data, wrote and edited the manuscript, created plots and visualisations. C.S contributed to data collection, provided conceptual guidance and contributed to editing the manuscript. S.S.U.A. provided administrative support. O.J contributed to movement data analysis. All authors commented on and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAcknowledgements\u003c/u\u003e: We acknowledge the help and support of the National Research and Innovation Agency (BRIN) and the Gunung Leuser National Park (TNGL) for the permission and essential administrative support provided to conduct this long-term research at the Suaq Balimbing Research Station. We also thank our affiliated institutions: the Magister of Biology Program, Faculty of Biology and Agriculture, Universitas Nasional, Jakarta, and the Max Planck Institute of Animal Behaviour, Germany, for their support. We thank YEL (Yayasan Ekosistem Lestari) and SOCP (Sumatran Orangutan Conservation Programme) for their collaboration, for hosting our project at the Suaq Balimbing Research station, and their contributions to supporting the research and conservation efforts in area. Finally, acknowledgement is given to the SUAQ Orangutan Program for the invaluable long-term data collection and logistical assistance in the field, and the team at Suaq Balimbing research site for their tireless and invaluable assistance with data collection.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ePapageorgiou D, Farine DR. Group size and composition influence collective movement in a highly social terrestrial bird. Elife [Internet]. Volume 9. eLife Sciences Publications Ltd; 2020. p. e59902. [cited 2026 Feb 10];. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.7554/eLife.59902\u003c/span\u003e\u003cspan address=\"10.7554/eLife.59902\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWebber Q, Albery GF, Farine DR, Pinter-Wollman N, Sharma N, Spiegel O, et al. 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Springer US; 1987 [cited 2018 Jun 13];8:17\u0026ndash;41. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/BF02737112\u003c/span\u003e\u003cspan address=\"10.1007/BF02737112\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"movement-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"move","sideBox":"Learn more about [Movement Ecology](http://movementecologyjournal.biomedcentral.com/)","snPcode":"40462","submissionUrl":"https://submission.nature.com/new-submission/40462/3","title":"Movement Ecology","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Foraging behaviour, spatial ecology, movement patterns, daily path length, sinuosity, fission-fusion dynamics","lastPublishedDoi":"10.21203/rs.3.rs-9574845/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9574845/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eSocial associations have well-established costs and benefits, and likely play a fundamental role in shaping animals\u0026rsquo; movement. Individuals are predicted to balance the benefits of associating, including social learning and mating opportunities, against key costs such as feeding competition, resulting in context-dependent movement patterns. However, the effects of the immediate social environment on movement remain poorly understood, likely because most movement ecology research focusses on either strictly group living or solitary species. We investigate how social associations shape fine-scale movement patterns and food resource exploitation in wild, semi-solitary Sumatran orangutans (\u003cem\u003ePongo abelii\u003c/em\u003e) who show fission-fusion social dynamics. We integrated 16 years of spatial data on 72 individuals with detailed behavioural observations. We predicted that associations shape movement in ways that reflect distinct benefits and costs across age-sex classes.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe quantified the effects of associations on daily path length (a proxy for energetic investment in movement) using continuous-time movement models, path sinuosity (as a measure of movement efficiency), and the use of key food hotspots (as an indicator of feeding competition and spatial knowledge). Using linear mixed models, we tested how these metrics varied with time spent in association and age-sex class, controlling for ecological factors.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eAcross all age-sex classes, daily path length increased with time in association, driven by longer active periods. At the population level, there was a trend towards straighter paths when individuals were with associates, though this depended on the class of the focal and the associate. Foraging behaviour was socially-sensitive, with all age-sex classes visiting fewer feeding hotspots when in associations, and spending less time feeding within them. Social influences on movement and foraging were most apparent in mothers, although flanged males also exhibited significant effects, including the greatest reduction in overall feeding time when in the presence of unflanged males compared to when alone.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eTogether, these results suggest that social associations entail costs and benefits for orangutans that are tangibly reflected in their movement and foraging decisions. Furthermore, different age-sex classes showed distinct adjustments in movement depending on who they associated with, highlighting the dynamic nature of social influences on behaviour.\u003c/p\u003e","manuscriptTitle":"The immediate social environment dynamically shapes movement and foraging in wild Sumatran Orangutans (Pongo abelii)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-12 13:16:38","doi":"10.21203/rs.3.rs-9574845/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"52617332182737403265360177650343536850","date":"2026-05-06T19:15:46+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-04T16:56:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-04T13:10:02+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-04T13:09:09+00:00","index":"","fulltext":""},{"type":"submitted","content":"Movement Ecology","date":"2026-04-30T09:14:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"movement-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"move","sideBox":"Learn more about [Movement Ecology](http://movementecologyjournal.biomedcentral.com/)","snPcode":"40462","submissionUrl":"https://submission.nature.com/new-submission/40462/3","title":"Movement Ecology","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"34b8ac8e-4fc6-4844-8883-6b12356e3a5c","owner":[],"postedDate":"May 12th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"52617332182737403265360177650343536850","date":"2026-05-06T19:15:46+00:00","index":10,"fulltext":""},{"type":"reviewersInvited","content":"7","date":"2026-05-04T16:56:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-04T13:10:02+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-04T13:09:09+00:00","index":"","fulltext":""},{"type":"submitted","content":"Movement Ecology","date":"2026-04-30T09:14:22+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-13T07:13:48+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-12 13:16:38","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9574845","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9574845","identity":"rs-9574845","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}