Family members in the cooperatively-breeding giant babax adjust their movement patterns in accordance with the labor division and requirements of parental care across seasons

Family members in the cooperatively-breeding giant babax adjust their movement patterns in accordance with the labor division and requirements of parental care across seasons | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Ecology and Evolution This is a preprint and has not been peer reviewed. Data may be preliminary. 12 November 2025 V1 Latest version Share on Family members in the cooperatively-breeding giant babax adjust their movement patterns in accordance with the labor division and requirements of parental care across seasons Authors : Ning-Ning Sun , Jian-Chuan Li , rang li 0009-0000-9006-6297 , Zhuo-Feng Li , Rong-Yu Xu , Miao Cheng , Shu-Min Wang , Li-Qing Fan , and Bo Du 0000-0003-1128-9164 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.176297986.67042666/v1 276 views 169 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The division of labor represents a crucial characteristic of cooperation that is linked to diverse strategies employed by group members when utilizing spaces and resources. In cooperatively-breeding species, dominants and helpers typically exhibit distinct parental care behaviors. However, it remains unclear whether the labor division serves as a mechanism for such differences. To address this question, we used GPS tracking to precisely determine the home range sizes, locomotor speeds, and activity levels of dominant breeders and helpers in the giant babax (Babax waddelli). Our results indicated that helpers occupied larger home ranges than did dominant breeders throughout all seasons. During the breeding season, when parental care is essential for offspring, helpers foraged more frequently in higher-altitude areas that were relatively distant from the nest, whereas dominant breeders primarily performed foraging near the nest. The temporal variation in movement patterns of dominant breeders differed significantly from that of helpers. During the post-fledging season, when offspring require less parental care, helpers continued to forage at higher altitude; and the movement patterns of dominant breeders and helpers tended to complement one another. During the wintering season, when offspring no longer require parental care, helpers foraged at lower altitude than dominant breeders, and no differences were observed in their movement patterns. These findings provided evidence that a division of labor indeed occurred in giant babaxes when offspring were in need of parental care. Therefore, labor division serves as the underlying mechanism for distinct parental care strategies adopted by dominant breeders and helpers. Title: Family members in the cooperatively-breeding giant babax adjust their movement patterns in accordance with the labor division and requirements of parental care across seasons Abstract The division of labor represents a crucial characteristic of cooperation that is linked to diverse strategies employed by group members when utilizing spaces and resources. In cooperatively-breeding species, dominants and helpers typically exhibit distinct parental care behaviors. However, it remains unclear whether the labor division serves as a mechanism for such differences. To address this question, we used GPS tracking to precisely determine the home range sizes, locomotor speeds, and activity levels of dominant breeders and helpers in the giant babax ( Babax waddelli ). Our results indicated that helpers occupied larger home ranges than did dominant breeders throughout all seasons. During the breeding season, when parental care is essential for offspring, helpers foraged more frequently in higher-altitude areas that were relatively distant from the nest, whereas dominant breeders primarily performed foraging near the nest. The temporal variation in movement patterns of dominant breeders differed significantly from that of helpers. During the post-fledging season, when offspring require less parental care, helpers continued to forage at higher altitude; and the movement patterns of dominant breeders and helpers tended to complement one another. During the wintering season, when offspring no longer require parental care, helpers foraged at lower altitude than dominant breeders, and no differences were observed in their movement patterns. These findings provided evidence that a division of labor indeed occurred in giant babaxes when offspring were in need of parental care. Therefore, labor division serves as the underlying mechanism for distinct parental care strategies adopted by dominant breeders and helpers. Key words: giant babax; GPS tracking; home range; labor division; movement pattern Introduction The division of labor among group members has long been regarded as a typical characteristic of cooperation in organisms (Beshers and Fewell 2001). This phenomenon spans across a wide spectrum of life forms, encompassing cells (Pulendran 2006), bacteria (Geerlings et al. 2020) and yeast (Wloch-Salamon et al. 2017), as well as invertebrates (Jandt and Dornhaus 2011, Brahma et al. 2018), vertebrates (Hattori et al. 2005, Dijk et al. 2014, Zhang et al. 2024) and human beings (Smith and von Hippel 2022). Given that phenotypic diversity leads to divergence in the utilization of different types of resources among conspecifics (Whitman and Agrawal 2009, Taborsky 2017), the essence of labor division lies in the fact that cooperating individuals strategically focus on fully exploiting a particular resource type that they prefer differently, thereby enhancing the efficiency of resource utilization (Gotwald 1974, Rueffler et al. 2012). In cooperatively-breeding species, in addition to the paired female and male, there are extra adult individuals present at the nest acting as helpers in raising the offspring (Koenig and Dichinson 2004, Cockburn 2006). Previous studies have demonstrated that dominants and helpers display notable differences in their parental care behaviors (Hamilton et al. 2005; Cram et al. 2015). However, the role of labor division in shaping the different contributions of dominants and helpers to parental care remains largely unexamined. In social animals, including humans, the division of labor among group members is often linked to diverse spatial preferences (Kurland and Beckerman 1985, Wahl 2002, Grinsted et al. 2013), particularly in the context of food acquisition. When different types of food are spatially segregated, group members foraging at various locations can not only mitigate competitive interference among conspecifics but also enhance their respective feeding efficiencies, owing to the specialized skills of different individuals developed for consuming a particular food type (Hegrenes 2001, Utsumi et al. 2009, Sassi et al. 2010, Hawlena et al. 2011). Under such circumstances, the division of labor can be regarded as the most critical factor shaping task differentiation among group members. Consequently, examining whether members of the same group exhibit differences in spatial utilization can help determine whether labor division underlies distinct behavioral strategies among group members. Regarding spatial differentiation among group members, the most prevalent phenomenon is the selection of home ranges. Animal home range is defined as a restricted area where animals can obtain all types of limited resources during a specific life-history period (Burt 1943, Swihart and Slade 1985, Powell 2000). Therefore, accurately measuring the size of an individual’s home range and its movement pattern within that range is a fundamental prerequisite for demonstrating the evolution of individual behavioral strategies (Duthé et al. 2023, Zhang et al. 2024, Brownlee et al. 2025). The earliest investigations of animal home range relied on the spatial locations of trapped individuals to define the boundaries of a home range (Hacker and Pearson 1946, Hayne 1949). In these studies, individuals might potentially escape the trap even when present at a site, resulting in inaccurate determination of the boundaries (Allen 1943). Another approach, estimating a home range based on data collected through behavioral observations (Guilford et al. 2008), could underestimate the home range size due to physical obstacles that hamper the witness of animals. The introduction of radio telemetry techniques makes it possible to automatically record the positions of animals (Ringelman et al. 1982, Mellen et al. 1992, Glenn et a. 2004, Dahle et al. 2006). However, radio telemetry can only monitor tagged animals within a restricted range and necessitate recapturing the tagged animals to gather the data. Under such circumstances, GPS (global positioning system) tracking techniques emerge and become the most appropriate approach for studying animal home range. This approach allows for the long-distance monitoring of animals’ positions and collecting data at anytime and anywhere (Guilford et al. 2008, Kotzerka et al. 2010, Hoenner et al. 2012, Ferrarini et al. 2018, Murgatroyd et al. 2023, Cheng et al. 2024, Dutta and Krishnamurthy 2025). Nevertheless, due to their own weight constraints and limited battery lifespan, GPS loggers have not been extensively utilized in the research of small-bodied animals, particularly resident passerines that remain within a restricted range throughout the year. The Giant babax ( Babax waddelli ) belongs to the Family Ptilornithidae (Aves, Passeriformes) that inhabits exclusively the Qinghai-Xizang Plateau (Lu 2004). It is an obligate cooperatively-breeding species, where all families contain helpers that are offspring of the paired breeders, with the numbers ranging from three to eight (Du et al. 2012). Although clutch size of six has occasionally been documented, most giant babax clutches have a fixed size of three (Liu et al. 2023), implying that some helpers have delayed their dispersal and act as helpers for several years. Helpers undertake multiple tasks in an extended family, including nestling provisioning, nest defending, and expelling both inter- and intra-specific intruders from their territories (Du et al. 2012). During the nestling period, helpers play a crucial role in provisioning the nestlings and their contributions are equivalent to that of the dominant female (Fan et al. 2018). Given the presence of multiple helpers within a single family of the giant babax, it is reasonable to postulate that labor division among family members is inevitable. However, to date, the validity and quantification of such labor division remain unresolved issues. In this study, we employed GPS tracking to explore the variations in home range sizes of dominant females/males and helpers of the giant babax, as well as their movement patterns, during the breeding, offspring post-fledging, and wintering seasons. Our aims were to examine whether different types of adult exhibit: (1) distinct strategies regarding the selection of home range, (2) distinct strategies regarding space utilization within the home range, in terms of the vertical moving directions during foraging, and (3) distinct movement patterns during foraging, in terms of the locomotor speed and activity. Study area and population This study was conducted in the Xiongse valley (29 º 44 ´ N, 91 º 00 ´ E) in Qushui county, Xizang Autonomous Region, China, from November 2024 to September 2025. The altitude of this valley ranges from 3,600 m to 5,000 m. The plateau’s temperature semi-arid climate in this region is characterized of hot in summer and cold in winter, with a large temperature difference between day and night and concentrated precipitation. Approximately 90% of the precipitation falls between May and September. Along with the ascendant height, landscapes change from hulless barley ( Hordeum vulgare ) farmland and its associated poplar ( Populus platyphylla ), to Lhasa barberry ( Berberis hemsleyana Ahrendt) and Alpine willow ( Salix sclerophylla ) shrubberies, and to Tibetan Juniper ( Sabina tibetica ) forest and alpine scree vegetations. Giant babaxes prefer to construct their nests in the poplar at lower altitude and Lhasa barberry at higher altitude. In the giant babax, one life-history cycle can be partitioned into three stages: the breeding season, the offspring post-fledging season, and the wintering season. The breeding season commences in mid-April and concludes in late May, encompassing the period from nest construction to the fledglings’ departure from the nest. The offspring post-fledging season extends from late May to September, coving the time from when all offspring in the population fledge until the new young are able to forage independently. The wintering season lasts from late October to late May of the following year. In this study, we utilized data collected between mid-November and early January as the wintering data. This is because the GPS loggers ceased to transfer data due to the failure of the solar cells to charge. GPS tracking of different family members in the giant babax To precisely track the movement behaviors of giant babaxes, mist nets were employed to capture these birds when they were foraging on the ground. The capture procedure was carried out in mid-November 2024. In this study, a total of eleven adult giant babaxes were randomly chosen from four families, successfully captured, and tagged with GPS logger. The identity of a tagged individual was determined based on its brood match, if the individual was recaptured during the breeding season (Liu et al. 2023). Specifically, female breeders exhibit an obvious brood patch that covers the entire abdominal area, male breeders have a smaller brood patch covering approximately one-third of the abdominal area, and helpers show no visible brood patch. If a tagged individual was not recaptured but was tracked during the breeding season, its identity was verified according to its behaviors: dominant females typically carry out the full-day incubation and brooding of the nestlings, dominant males only occasionally carry out the incubation and brooding when the dominant female was off the nest, while helpers never carry out incubation and brood of the nest (Liu et al. 2023). Among these eleven tagged individuals, two disappeared during the tracking, two were recognized as dominant females, three were recognized as dominant males, and the remaining four individuals served as helpers. Body parameters of these adults, including body mass (to the nearest 0.01 g), body length and tarsus length (to the nearest 0.1 mm), were first measured before they were tagged. Then, a backpack-style GPS transmitter (HQBG1202; Global Messenger Technology Co., Hunan Province, China) was used to carry out the tracking. A GPS transmitter was weight 2.9 g, which is significantly less than 3% of the body mass of giant babaxes (ranging 130-140 g, n = 20 individuals). The GPS transmitter was affixed dorsally using a supple nylon cord passed through the device’s attachment loop. The cord was secured to the scapular feathers with controlled tension –maintaining a gap approximately of 20 mm between the tracker and the body, aiming at preventing feathers from compressing while ensuring device retention and unimpeded flight capability. GPS transmitters were deployed with location acquisition scheduled every hour. Data transmission was triggered once five position fixes were stored. All individuals were released immediately after the GPS transmitter was attached. Then, the flight behaviors of these tagged individuals were monitored with binoculars. Behavioral observations confirmed that these tagged individuals did not display any abnormal flight patterns (such as lateral instability or reduced lift). Additionally, it appeared that giant babaxes spent most of their daily times foraging. Thus, when the GPS tracker indicated that a giant babax was at a certain speed, it was likely that it engaged in foraging. This movement was recorded as a foraging event. Field re-sightings verified that giant babaxes are resident and exhibit home range fidelity, because tagged individuals were present in our study area throughout the year. During the breeding season, giant babax nests were located by systematically searching in the poplar and Lhasa barberry shrubs. An active nest was monitored throughout the breeding season. The GPS coordinate data of each nest were recorded to examine where it was located within the home range of a tagged individual. Tagged individuals that belonged to an active nest were monitored to record their behaviors using binoculars, by which we could identify their identities according to their behaviors. Data curation The retrieved tracking data comprised timestamp (GMT+8), longitude, latitude, altitude (m, ASL), position accuracy, instantaneous locomotor speed (km/h), and activity level. Position accuracy refers to the proximity between a satellite-derived position and its true location on Earth. Activity level was derived from triaxial accelerometer readings: during each sampling cycle, the cumulative count incremented by 1 whenever acceleration exceeded 0.15g in any axis (X, Y, or Z), aligning with avian movement models (Shepard et al. 2008, Halsey 2011, Halsey et al. 2015). Home range sizes of these ten individuals in different seasons, as well as their core area sizes, were calculated according to the farthest position in eight distinct directions within a specific season, i.e., the method of minimum convex polygon (MCP)(Worton 1989). Home range analysis was performed using software Tracker Client (v3.0406, HQXS com.). MCP included 99% of the locations to construct the smallest convex polygon, which was defined as the home range. Moreover, it included the innermost 50% of points to construct a convex polygon, which was defined as the core area of a home range. Due to the challenges associated with continuously and longitudinally observing the foraging behaviors of giant babaxes, we screened out GPS tracking data (from 5:00 to 20:00) with recorded locomotor speeds greater than zero as an indicator of foraging events. This is based on the fact that adult giant babaxes allocated a significant portion of their daily time to foraging in order to meet their nutritional requirements. Consequently, positions with locomotor speed greater than zero were, to a large extent, recorded at their foraging sites. Statistical analysis The altitudes of dominant females, dominant males and helpers in each season were compared using one-way ANOVA. In order to control for the dependence resulting from repeatedly sampling of the same individual, different values of the three variables, which were collected in multiple days for one individual, were averaged before performing the comparison. Generalized linear mixed models (GLMMs) were fitted to examine the temporal variations in locomotor speed and activity levels of giant babaxes with seasonal days and daily times in each of the three seasons. The locomotor speed and activity level of an individual were set as the dependent variable, respectively, with normal distribution and an identify link function. Fixed effect variables included the identity of an individual (dominant female, dominant male, or helper, set as the categorical variable), seasonal days and daily times (numeric variables), and the interplay between individual identity and seasonal days or daily times. The identity of an individual was set as the random effect variable as it had been repeatedly sampled in different seasonal days. In order to obtain an optimized model, we first obtained a maximal model by introducing the main effect of these three fixed effect variables and their mutual interactions into the model. Then, items with no significant impact on the dependent variable were removed from the model one-by-one, until the Akaike’s information criterion (AIC) reached a minimum value. The predicted value of a dependent variable, which was acquired in fitting the optimal GLMM, was saved as a new variable. Then, it was regressed against the seasonal days following a linear model and against daily times following a quadric model, to examine its temporal variation for different types of adults, using curve estimation. GLMM analyses and associated linear regression were performed using R (version, R Core Team 2018). The visualization of the statistical results was accomplished by ggplot 2 (Wickham 2016). Descriptive results are presented as mean ± SEM, and overall significance was evaluated based on P two-tailed < 0.05, indicating rejection of the null hypothesis. Results Using GPS tracking, we obtained data about giant babaxes’ home range sizes, altitude at which individuals were located, their locomotor speed and activity levels with a specific duration. The comparison among dominant females, dominant males and helpers indicated that different individuals might adopt distinct strategies in selecting the home range and movement patterns. Movement directions of giant babaxes in different seasons The home ranges sizes of nine tagged adults were quantified in each of the three seasons (Figure 1). During the breeding season, dominant females moved within the smallest range, whereas helpers moved within the largest one (Figure 1A-1C). Dominant females and males predominantly foraged in the vicinity of the nest site (Figure 1A,1B), while helpers foraged in a remarkably larger range compared to dominants (Figure 1C). During the post-fledging season, dominants continued to move near the nest site (Figure 1D-1E), while helpers moved to areas farther from the nest site (Figure 1F). Notably, dominant females significantly expanded their foraging ranges compared to those in the breeding season (Figure 1D). During the wintering season, all individuals tended to move and forage mainly within their core areas (Figure 1G-1I). Occasionally, helpers moved a considerably greater distance to the locations occupied by other families (Figure 1I). The altitudes at which different adults were off the nest and foraged were compared using one-way ANOVA. The results indicated that the preferences for foraging site exhibited significant differences between helpers and dominant breeders. In the breeding season, dominant females and males tended to forage in the vicinity of the nest, whereas helpers foraged at higher altitude. There was no significant difference in their foraging ranges between helpers and dominant females and males (Figure 2A). In the offspring post-fledging season, helpers tended to forage at the highest altitude while dominant females at the lowest altitude, and the foraging range of dominant females was obviously larger than that of dominant males and helpers (Figure 2B). In the wintering season, helpers foraged at the lowest altitude and their foraging ranges were obviously larger than that of dominant females and males (Figure 2C). Movement patterns of giant babaxes in the breeding season During the breeding season, the locomotor speed of giant babaxes exhibited no significant differences between helpers and dominant females/males, and it did not change significantly with daily times but tended to change with seasonal days (Table S1). Regarding each type of group members, the locomotor speed of dominant males differed significantly from that of helpers, which decreased significantly with both seasonal days (Figure 3A) and daily times (Figure 3B; Table S1). By contrast, the locomotor speed of dominant females exhibited no significant difference from that of helpers, neither of them changed significantly with seasonal days (Figure 3A) and daily times (Figure 3B; Table S1). The activity level of giant babaxes exhibited no significant differences between helpers and dominant females or males, and it changed significantly with both the seasonal days and daily times (Table S2). Regarding each type of group members, their activity levels all increased significantly with seasonal days, and there was no significant difference between dominant female and helpers, whereas the level activity of dominant male was significantly lower than that of helpers (Figure 3C). Their activity levels changed with daily times following a quartic pattern, with the level being greatest at noon (Figure 3D). Movement patterns of giant babaxes in the post-fledging season During the offspring post-fledging season, the locomotor speeds of giant babaxes exhibited no significant differences among dominant females/males and helpers, and it did not change significantly with seasonal days (Figure 4A) and daily times (Figure 4B; Table S3). The activity level of giant babaxes in the offspring post-fledging season was unrelated to the types of adults and it tended to change significantly with both the seasonal days and daily times (Table S4). Regarding each type of group members, the activity level of dominant females was significantly lower than that of helpers (Table S4), whereas the activity level of dominant males exhibited no significant difference from that of helpers (Table S4). Dominant females decreased activity level significantly with seasonal days, whereas dominant males and helpers increased activity levels with seasons days (Figure 3C). Dominant females and males displayed the lowest activity levels at noon, whereas helpers displayed the highest activity levels at noon (Figure 3D). Movement patterns of giant babaxes in the wintering season During the wintering season, the locomotor speed of giant babaxes exhibited no significant differences among dominant females/males and helpers, and it did not change significantly with seasonal days but changed significantly with daily times (Table S5). Specifically, helpers significantly decreased their locomotor speed with seasonal days whereas dominant females and males did not change their locomotor speed with seasonal days (Figure 5A). Helpers exhibited the largest speed at noon, whereas dominant females and males did not change their locomotor speed with daily times (Figure 5B). The activity level of giant babaxes in the wintering season exhibited no significant differences among dominant females/males and helpers, and it changed significantly with both the seasonal days and daily times (Table S6). Regarding each type of group members, all adults increased their activity levels with seasonal days (Figure 5A), and dominant females exhibited significantly greater activity level than that of helpers, whereas dominant males and helpers exhibited no significant differences (Figure 5A; Table S6). The activity levels of dominant males and helpers did not differ significantly and they exhibited the largest value at noon (Figure 5D). Dominant females displayed significantly larger activity level that helpers but they did not change their activity levels with daily times (Figure 5D). Discussion Utilizing GPS tracking data of the giant babax, we quantified the individual home range sizes, moving directions, locomotor speeds, and activity levels during the breeding, offspring post-fledging, and wintering seasons. By conducting a comparison between dominant females/males and helpers, we identified significant differences in their spatial utilization and movement patterns. These findings thereby provide evidence for the division of labor among group members within the extended families of giant babaxes. Division of labor took place in the giant babax during the breeding season In cooperative breeding systems, diverse parental care strategies among group members have been documented (Hatchwell 1999, Cuckburn 2006). This diversity might have resulted from a negotiation among them (Kokko et al. 2002, Magrath et al. 2004), or alternatively, through a division of labor (Shimoji and Dobata 2022). The key distinction between these two underlying mechanisms lies in whether there is a divergence in the utilization of space and food types among group members. In the former case, the partitioning of parental care among group members is closely linked with their reproductive shares (Kokko et al. 2002, Robertson et al. 2018), seemingly unrelated to their potential specialized capacity of utilizing specific types of resources. Conversely, in the latter mechanism, a clear differentiation can be manifested not only in the emergence of reproductive and non-reproductive individuals but also in the spatial structure of nonreproductive individuals in conducting their helping behaviors (Shimoji and Dobata 2022). Therefore, whether spatial and resource utilization differentiates between dominants and helpers determines the underpins of diverse behavioral strategies within a cooperative-breeding system. In the giant babax, our study confirmed that labor division indeed took place during the breeding season, which serves as the primary factor attributing to the different parental care behaviors among family members (Fan et al. 2018). There are two lines of evidence demonstrating the labor division between dominant breeders and helpers. Firstly, compared to dominant females and males, helpers occupied larger home ranges and foraged at greater distances from the nest site (Figure 1A-1C). This suggests that dominants and helpers employed distinct strategies in spatial utilization. Secondly, helpers tended to forage at higher altitude sites than dominant females and males (Figure 2A), indicating that helpers adopt different strategies in food resource utilization compared to the dominants. Consequently, labor division is the most plausible explanation for the differentiation in parental care behaviors in the giant babax, rather than negotiation between dominants and helpers. The division of labor between dominants and helpers in the giant babax contributes to the optimization of parental care efficiency in provisioning nestlings. Regarding dominant females, given the substantial energy expenditure during egg-laying and brooding, they tend to adopt energy-saving strategies in their foraging. Staying close to the nest area can shorten the travel time to and from the nest, thus saving energy during flight. The dominant males, who bear the largest share of parental care (Fan et al. 2018), need to obtain more food within a unit of time. Therefore, foraging near the nest helps save time on the way. Thus, in terms of spatial utilization, the dominant females and males mainly use the core area. As helpers are numerous in the giant babax (Du et al. 2012), their feeding duties can be shared. Foraging at higher altitudes and farther away from the nest helps reduce the overlap with dominant individuals near the nest area and increase the utilization of food resources at the home range boundary. Therefore, helpers mainly exploit the boundary area. The disparities in spatial and food utilization between dominants and helpers reflects their coordination and cooperation during the brooding process. The differences in the selection of home range (Figure 1) and foraging altitude (Figure 2) between dominants and helpers indicate that labor division persisted into the post-fledging period but ceased during the wintering season. This is attributed to the fact that during the post-fledging period, helpers remained in high-altitude regions for foraging (Figure 2B), whereas during the wintering season, helpers foraged in lower-altitude habitats (Figure 2C). Given that giant babax offspring depend on post-fledging care for an extended duration before they are able to forage dependently, the patterns of helpers foraging at higher altitude while dominants at lower altitudes could optimize the feeding efficiency of dominant breeders. During the wintering season when juveniles no longer require feeding assistance, the movement of helpers within a larger, lower-altitude habitat may enable them to access a greater quantity of food resources and, simultaneously, establish connections with individuals from other families. Trade-offs between parental care and energy saving across seasons Energy costs associated with foraging activities are an important factor driving individuals to optimize their foraging strategies (Krebs 2014), and prompting the diversification of foraging strategies among group members as well (Lendvai et al . 2004, 2006). For example, when house sparrows ( Passer domesticus ) feed in flock, hungry individuals are more likely to adopt scrounging strategy compared with when they are satiated (Lendvai et al. 2004), and dominant individuals adopt scrounging strategy uniformly whereas subordinates only adopt scrounging opportunistically (Lendvai et al. 2006). Under the conditions with energy challenges, such as the high-altitude environments that giant babaxes inhabit, the temporal variations in the movement patterns of giant babaxes demonstrated a clear association between parental care and energy saving. Compared with the post-fledging and wintering seasons, giant babaxes in the breeding season are compelled to allocate a substantial portion of food to nestlings. This necessity drives them to optimize their movement patterns during the foraging process. As nestlings grow and their food requirements increase, dominant females and males adjust their foraging behaviors by decreasing speed while increasing overall activity levels. This adjustment allows them to maintain a relatively stable energy expenditure. In contrast, helpers increase both their speed and activity, ensuring that a greater amount of food can be delivered to the nest. This strategic divergence between dominants and helpers results in helpers making a relatively larger contribution to nestling provisioning as nestlings develop. Within a single day, nestlings exhibited the highest demand for food at dawn. To meet this need promptly, dominants adopt a foraging strategy characterized by high speed and low activity, enabling them to feed the nestlings as quickly as possible. Moreover, all individuals tend to exhibit the highest level of activity at noon (Fig. 3D-5D). This pattern may serve to reduce the energy expenditure required to maintain body temperature in cold environments. Collectively, these findings suggest that dominant breeders and helpers adopt distinct foraging strategies; and that these strategies complement each other, optimizing the trade-off between parental care and energy saving. During the post-fledging season where offspring gradually decrease their dependence on parental care, giant babaxes exhibited no temporal variation in their locomotor speed but temporal adjustment of activity levels. Similarly, dominants and helpers complement each other so that new fledglings could receive a stable amount of food from the provisioners. When offspring do not require parental care during the winter season, no differences were observed in the temporal variations of both locomotor speed and activity level between dominant breeders and helpers. This suggests that the labor division between dominants and helpers disappeared, and all individuals adjusted their movement patterns to minimize energy expenditure, as previously discussed. The distinct movement patterns of giant babaxes across different seasons confirm that the division of labor among group members serves as the foundation for individual trade-offs between parental care and energy saving in the high-altitude environment. Adaptive responses of dominants to the presence of helpers In cooperatively-breeding groups, the presence of helpers facilitates dominant breeders, particularly the females, to adjust their workload in providing parental care for the dependent offspring (Heinsohn 2004). By reducing maternal investment during provisioning the nestlings (Zöttl et al. 2013, Adams et al. 2015, Hirokazu et al. 2018, Mermoz et al. 2025) or increasing maternal investment during laying the eggs (Capilla-Lasheras et al. 2023, Cones et al. 2023), dominant breeders can benefit from such adaptive responses to the compensatory contribution of helpers, in terms of enhanced offspring survival. Although our prior studies have revealed that the presence of helpers is crucial for ensuring the survival of offspring in the giant babax (Fan et al. 2018, Liu et al. 2023), our current study for the first time presents evidence that dominant breeders can modify their movement patterns during the breeding season in response to the presence of helpers at the nest. Utilizing GPS tracking technology, we confirmed that the presence of helpers might substantially diminish the energy consumption of dominant breeders during the process of provisioning nestlings. Regarding dominant females, apart from the minimal contribution they are required to make to nestling provisioning (Fan et al. 2018), they can also conserve energy by shortening foraging travel distances (Figure 1A). For dominant males, despite their crucial role in nestling provisioning (Fan et al. 2018), the presence of helpers enables them to forage in the vicinity of the nest site, thereby facilitating the tasks of providing paternal care for nestlings to be easily accomplished. Therefore, dominant males can conserve energy as well during foraging within a limited home range. This exemplifies that both dominant females and males in the giant babax may obtain benefits, in terms of enhanced feeding efficiency and simultaneously reduced energy expenditure, from the limited home and foraging ranges. The potential for improvement of this study Obviously, the largest shortcoming of this study is attributed to the small sample size. Given the endangered status of the giant babax and the expensiveness of GPS loggers, the number of adult individuals tagged in this study was restricted. As the giant babax does not display sexual dimorphism in plumage, it was not feasible to selectively choose the tracking subjects during winter. The random selection of eleven adult individuals results in the tracking of only two dominant females and three dominant males in this study. Therefore, although the comparison results regarding the movement patterns of dominant females/males and helpers appear to align with the intuitive understanding and provisioning behaviors reported in previous studies (Liu et al. 2023), the reliability and generality of this finding still require further validation using a larger sample size. An additional limitation of this study lies in the low coverage in sampling helpers because there are at least five helpers in an extended family of the giant babax. The random selection of tagged subjects resulted in the tracking of at most two helpers within a family. Considering that different helpers may undertake different tasks in the giant babax (Fan et al. 2018), the home range selection and movement patterns revealed in this study might not accurately represent the behavioral characteristics of all helpers. Furthermore, the inability to determine the sex of helpers weakened our understanding of the labor division among multiple helpers within the same family. Likewise, the crucial approach to addressing this shortcoming is to increase the sample size. Conclusion By applying GPS tracking to monitor giant babaxes across various seasons, the present study has confirmed that dominant females and males, as well as helpers, exhibited different selection of home ranges during the breeding season, which resulted in distinct strategies between them in space utilization and movement patterns during foraging. 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Collection Ecology and Evolution Keywords behavioral ecology ecological experiment terrestrial vertebrate Authors Affiliations Ning-Ning Sun Lanzhou University School of Life Sciences View all articles by this author Jian-Chuan Li Xizang Museum of Natural Science View all articles by this author rang li 0009-0000-9006-6297 Lanzhou University School of Life Sciences View all articles by this author Zhuo-Feng Li Xizang Museum of Natural Science View all articles by this author Rong-Yu Xu Lanzhou University School of Life Sciences View all articles by this author Miao Cheng Lanzhou University School of Life Sciences View all articles by this author Shu-Min Wang Lanzhou University School of Life Sciences View all articles by this author Li-Qing Fan Xizang Agricultural and Animal Husbandry University View all articles by this author Bo Du 0000-0003-1128-9164 [email protected] Lanzhou University School of Life Sciences View all articles by this author Metrics & Citations Metrics Article Usage 276 views 169 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Ning-Ning Sun, Jian-Chuan Li, rang li, et al. Family members in the cooperatively-breeding giant babax adjust their movement patterns in accordance with the labor division and requirements of parental care across seasons. Authorea . 12 November 2025. DOI: https://doi.org/10.22541/au.176297986.67042666/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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