Behavioural effects of persistent human disturbance: a playback experiment in a forest bird

Behavioural effects of persistent human disturbance: a playback experiment in a forest bird | 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 Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 31 March 2025 V1 Latest version Share on Behavioural effects of persistent human disturbance: a playback experiment in a forest bird Authors : András Liker 0000-0001-8545-4869 [email protected] , Csenge Sinkovics , Krisztina Sándor , Boglárka Bukor , Nóra Nagy , Levente Ódor , Krisztián Klucsik , and Nóra Ágh Authors Info & Affiliations https://doi.org/10.22541/au.174343336.67337980/v1 Published Ecology Letters Version of record Peer review timeline 403 views 252 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Increasing human presence and activities in the environment of wild animals expose them to persistent disturbances. Individuals in disturbed populations often become tolerant towards humans, although the underlying mechanisms are poorly understood. We used playback experiments to manipulate perceived level of human disturbance during breeding in wild great tits (Parus major). We found that incubating females remained more often on the nest, and parents caring for their nestlings exhibited lower level of vigilance and shorter return latencies after standard disturbances in human disturbance treatment than in control treatments. The tolerance of birds increased with time, and was influenced by multiple disturbance sources including the frequency of nest visits by observers and distance to roads. These results support that behavioural tolerance can quickly emerge by phenotypic plasticity in natural populations. The spread of tolerant populations can have significant effects in ecological communities and on their interactions with humans in anthropogenic environments. Behavioural effects of persistent human disturbance: a playback experiment in a forest bird András Liker 1,2 , Csenge Sinkovics 1,2 , Krisztina Sándor 3 , Boglárka Bukor 1,2 , Nóra Nagy 4,5 , Levente Ódor 6 , Krisztián Pál Klucsik 1 , Nóra Ágh 1,2 1 Behavioral Ecology Research Group, Center for Natural Sciences, University of Pannonia, Veszprém, Hungary 2 HUN-REN-PE Evolutionary Ecology Research Group, University of Pannonia, Veszprém, Hungary 3 Balaton Uplands National Park Directorate, Csopak, Hungary 4 Department of Zoology, University of Veterinary Medicine, Budapest, Hungary 5 Department of Environmental Protection, Government Office of Heves County, Eger, Hungary 6 Németh László Highschool, Budapest, Hungary E-mai addresses : AL, primary: [email protected] , secondary: [email protected] ; CS: [email protected] ; KS: [email protected] ; BB: [email protected] ; NN: [email protected] ; LO: [email protected] ; KPK: [email protected] ; NÁ: [email protected] Running title: Behavioural effects of human disturbance Keyewords: human disturbance, disturbance tolerance, learning, habituation, phenotypic plasticity, urbanization, anthropogenic environment Type of article: Letter Word counts : abstract: 150, main text (excluding abstract, acknowledgements, references, table and figure legends): 4987, text box: 0 Number of references: 50 Number of figures: 3, tables: 1, text boxes: 0 Number of supporting figures: 6, tables: 3, text boxes: 0 Corresponding author: Andras Liker, University of Pannonia, Pf. 158, H-8201 Veszprém, Hungary, Tel: +36 88 624568, Fax: +36 88 624747, email: [email protected] Statement of authorship: AL conceived the study. AL, CS and KS designed the fieldwork. AL, CS, KS, BB and NN collected the data. AL, NÁ and NN analysed the data. KK and LO developed and produced the devices and software used in the experiments. AL wrote the manuscript with substantial inputs from all authors. Conflict of interest statement: All authors declare that they do not have any conflict of interests. Data accessibility statement: The authors confirm that the data and code supporting the results have been archived in Figshare, DOI: 10.6084/m9.figshare.28683524, and can be accessed for review through this link: https://figshare.com/s/6202b21d0e0d8a2eda20 Abstract Increasing human presence and activities in the environment of wild animals expose them to persistent disturbances. Individuals in disturbed populations often become tolerant towards humans, although the underlying mechanisms are poorly understood. We used playback experiments to manipulate perceived level of human disturbance during breeding in wild great tits ( Parus major ). We found that incubating females remained more often on the nest, and parents caring for their nestlings exhibited lower level of vigilance and shorter return latencies after standard disturbances in human disturbance treatment than in control treatments. The tolerance of birds increased with time, and was influenced by multiple disturbance sources including the frequency of nest visits by observers and distance to roads. These results support that behavioural tolerance can quickly emerge by phenotypic plasticity in natural populations. The spread of tolerant populations can have significant effects in ecological communities and on their interactions with humans in anthropogenic environments. 1 Introduction The presence and activity of humans typically provokes fear responses in wild animals and may disrupt their natural behaviour (human disturbance; Frid & Dill 2002; Tablado & Jenni 2017). However, animals living in environments where they regularly face disturbances may become tolerant towards humans, and this change in fear response is consistently observed in different types of disturbance regimes, habitats, and taxonomic groups (Blumstein 2016; Čapkun-Huot et al. 2024; Geffroy et al. 2020; Samia et al. 2015). Responses of wild animals to human disturbances (both by fear and tolerance) are becoming an increasingly important research field, because disturbance effects can have complex impacts on populations’ demography and their interactions in ecological communities (Smith et al. 2024), and also have practical implications for societal issues including ecosystem services, human-wildlife conflicts, and conservation (Blumstein 2016; Smith et al. 2024; Uchida et al. 2024). Although a large number of studies have been focusing on disturbance tolerance in wildlife worldwide, the underlying behavioural and evolutionary mechanisms remained largely untested (Uchida & Blumstein 2021). One of the most often proposed mechanism behind the emergence of behavioural tolerance is some form of learning, proposing that the repeated exposure of animals to proximity of non-harmful humans results in the diminishing of fear response (Čapkun-Huot et al. 2024). This can occur through habituation, when responsiveness to a stimulus decreases with repeated presentations making it less likely that the individuals will respond to harmless stimuli (Blumstein 2016; Rankin et al. 2009). Another potential mechanism is fear extinction, a form of inhibitory learning occurring when the association of a stimulus with a harmful outcome is not reinforced in subsequent presentations of the stimulus, leading to the reduction or elimination of fear responses (Herry et al. 2010). Increased tolerance to humans also can be transferred by social learning between individuals, for example from habituated parents to their offspring (Schell et al. 2018). All these forms of learning allow relatively quick responses to changes in ecological conditions, hence may be crucial mechanisms involved in the emergence of tolerance when wild populations are exposed to human disturbance (Blumstein 2016; Čapkun-Huot et al. 2024). Alternatively, behavioural tolerance may become associated with disturbed environments due to phenotype-specific habitat choice (Carrete & Tella 2010). This hypothesis proposes that bold or tolerant individuals move into and settle more often in disturbed areas than the ones with less tolerant phenotypes. This idea is supported by some studies showing that individuals with bold behavioural types occur more frequently in disturbed urban areas than less bold individuals, and that behavioural plasticity is less likely to explain their spatial distribution (Carrete & Tella 2010; Holtmann et al. 2017; Sprau & Dingemanse 2017). Finally, evolutionary changes can also result in increased tolerance when the population is exposed to disturbance over the long term. Responding to disturbances by fear and flight have costs in terms of reduced time for feeding or parental activities, which ultimately may reduce fitness (Blumstein 2016; Čapkun-Huot et al. 2024; Frid & Dill 2002; Smith et al. 2024). Thus, when humans do not pose a real danger, animals can benefit from reduced responses and will have increased fitness relative to individuals with a stronger fear response. There is evidence for genetic bases of disturbance tolerance (Agnvall et al. 2018; Carrete et al. 2016; Møller 2014), thus beneficial tolerant genotypes can spread by natural selection in disturbed environments. Laboratory and correlative field studies have provided some support for all of the above, non-mutually exclusive hypotheses (Čapkun-Huot et al. 2024). However, there is a lack of controlled field experiments that test these alternatives by manipulating the intensity of human disturbance, thus in most cases it cannot be determined what mechanism(s) are involved in the development of behavioural tolerance in wild populations. Playback experiments can provide a suitable tool to manipulate the perceived level of risk or disturbance in the environment of natural populations. This approach has been successfully used to test the behavioural and reproductive effects of predators on their preys (Zanette et al. 2011, 2023), and is increasingly applied to investigate the effects of human disturbance on wildlife. Studies show that wild animals recognise and respond to playbacks of human speech (MacLean & Bonter 2013; McIvor et al. 2022; Zanette et al. 2023). Field studies found, for example, that increased human disturbance simulated by playbacks reduces habitat use by sensitive species and can alter local ecosystem composition (Bötsch et al. 2017; Smith et al. 2017; Suraci et al. 2019). However, to our knowledge, no manipulation by playbacks (or by other experimental approaches) has been applied to test how persistent human disturbance influences tolerance in wild populations. In this study, we investigated whether and how tolerance develops in response to frequent and persistent human disturbances in a population of wild great tits ( Parus major ). This species breeds along the disturbance gradient from natural forests to urban centres, and our earlier work showed markedly increased tolerance towards humans in disturbed habitats (Vincze et al. 2019, 2021). In the experiment, we simulated different levels of disturbance by playbacks around the nests of great tits breeding in a forest habitat where they rarely have been exposed to the presence of humans before the study. We conducted continuous disturbance treatments from egg laying until fledging and tested the parents’ behaviour repeatedly during incubation and brood rearing. Since the population (1) has been living in an environment largely free from earlier selection for disturbance tolerance, and (2) the manipulation started after the initiation of egg laying (i.e. after nest site selection), we could test the hypothesis that the birds’ tolerance behaviour is altered by phenotypic plasticity (e.g. learning). We conducted the experiments in both first and second broods within year and in two consecutive years, thus we could also investigate temporal changes in tolerance. Finally, some of our earlier results based on similar behavioural data (Vincze et al. 2021) allowed us to compare the experimental effects to tolerance level we see in urban populations that have been exposed to anthropogenic disturbance for many generations. 2 Methods 2.1 Study site and general fieldwork The study was conducted in a homogenous, mixed broadleaf forest in the Bakony Mountains, Hungary (47°11’48” N, 17°39’35” E; Fig. S1A). Most parts of the study site are relatively undisturbed most of the time, having only occasional human presence and activity. For the purpose of the experiment, we put up 150 nest boxes in the study area in January and early February in 2022, in seven spatial clusters corresponding to the experimental groups (see below). The distance between the nest boxes was 40-50 m, and their sites’ GPS coordinates were recorded. Nest boxes were monitored from early March to late June twice per week to find new clutches. Both first and second broods of great tits were included in the study, resulting in a total 28 and 82 broods in 2022 and 2023, respectively. We ringed 43 female and 33 male parents during the study (see Supporting methods S1 for more details on the study site and fieldwork). 2.2 Experimental design We divided the area into seven forest blocks, and allocated two or three forest blocks (containing a total of 50 nest boxes) to one of three experimental treatments. The blocks involved in the same treatment were located in different parts of the study area (Fig. S1B). To manipulate the intensity of human disturbance around the nest boxes, we applied one of three different playback treatments near active nests of great tits (i.e. after females started egg laying): (1) control treatment without playback (hereafter no-playback group), (2) control treatment where we played records of birdsongs (birdsong group), and (3) disturbance treatment where we played records of human talks (human disturbance group). In the last two treatments, we put up a purpose built, camouflaged speaker on a tree (Fig. S2) about 5 m from the nest box, approximately at the same height (3-5 m), facing in the direction of the nest box. Each player had a list of 15 records of either birdsongs or human talks. On average, records were played 7.5 times per hour between 6:00 and 18:00 (90 playbacks per day). The devices were set to produce sound volume of cc. 60 dB (measured at 1m distance), that is within the range of the volume of normal conversations (55 - 66 dB, Pearsons et al. 1977). The random order of the records, their variable length, and the random length of silent periods between them reduced the chance that birds could simply habituate to a particular record. To further reduce habituation to monotony of playbacks, the records were played for 3.5 days, followed by 3.5 days of continuously silent period (Fig. S3). This length of the silent periods is suitable to eliminate sound habituation (Chew et al. 1996; see Zanette et al. 2011 for a similar approach). The 7 days playback plus silent sequence was then repeated until the ringing of the nestlings, resulting in 5-6 playback period of 3.5 days at each nest (Fig. S3), depending on when the nest was found during egg laying and the length of the laying and incubation period of the clutch. To reduce site effect, we switched the treatments between the birdsong and human disturbance forest blocks in 2023. The no-playback forest blocks were the same in both years. The experiment involved 37 no-playback control broods (10 and 27 in 2002 and 2023, respectively), 37 (9 and 28) birdsong control broods and 36 (9 and 27) human disturbance broods. See Supporting methods S2 for further details on the playback experiment. 2.3 Behavioural data We used three behavioural proxies to quantify the birds’ tolerance to human disturbance during breeding. First, we tested the tolerance of females using the same procedure we applied in the study of Vincze et al. (2021). During nest checking when the observer approached and inspected the nest box, the behaviour of the female was recorded using the following categories: (1) Flying off: the female was seen flying off the nest while the observer approached the nest, or when the nest box was taken off the tree, or after the lid of the nest box was opened. (2) Staying: the female stayed on the nest after we opened the nest box’s lid until we closed the lid and put back the nest boxes to the tree. We omitted nest checks when the female was neither found on the nest nor seen flying off the nest. 91% of the retained observations (i.e. when females either flew off or stayed) were recorded during incubation or within 5 days after hatching when females often brood small nestlings. As male great tits do not incubate their eggs (Kluijver 1950; our personal observations), we assumed that the bird we saw flying off or found on the nest was the female (Vincze et al. 2021). On average, we recorded 3.3 ± 0.1 (mean ± SE) observations per brood (n= 108 broods). Staying on the nests by individual female great tits is repeatable both within and between years (R= 0.5 - 0.7), and is observed more frequently in urban than in forest populations (Vincze et al. 2021). We interpret staying on the nest during checking as a higher level of tolerance for human disturbance than flying off. Second, we conducted a standardized disturbance test during the brood rearing period to quantify the tolerance of both the male and female parents. For this purpose, we disturbed the parent birds at nest checking with the addition of a short playback of human talk plus putting a camera on the nest box (see Supporting methods S3 for details). We repeated this disturbance test three times at each nest during the brood rearing period, (1) between 4-7 days, (2) between 8-10 days, and (3) between 9-12 days after hatching. For nests where one or both parents were not ringed, we conducted at least two out of the three repeats of the test before catching the parents. From each video recording, we collected data for two behavioural variables. First, we scored the vigilance behaviour of the parents returning to the nest box according to a 4-score scale: (0) the bird went straight inside the nest box without hesitation ( 1 sec, and did not turned its head, (2) the bird waited > 1 sec and turned its head and looked around before entering, and (3) the bird stayed in an upright vigilant posture and/or stretched its neck and looked around, or turned around with back to the hole and watched the environment. Vigilance behaviour was scored three times for both parents on each video record, for the first three occasions when the bird entered the nest. Second, we recorded arrival latency (in sec) defined as the first appearance of the parents on the nest box (e.g. in the entrance or on the wooden plate to which the camera box was attached) after the observer left the site. Both the vigilance behaviour and the return latency were recorded separately for the male and female parent (n= 97 broods). We interpret lower vigilance scores and shorter return latency as indications for a higher level of disturbance tolerance. 2.4 Statistical analyses We selected those nests for data analyses that were found during laying and at least one nestling reached ringing age, thus we were able to carry out playback treatments from the egg laying until the ringing of nestlings. For each of the three behavioural variables, we constructed a separate linear mixed model with the behavioural variable as its response. The propensity of females to stay on the nest was analysed by a generalized linear mixed-effects model with binomial error distribution and logit link function. The model included female behaviour as a binary response (0: flying off, 1: staying) and experimental treatment (no-playback, birdsong, human disturbance) as a predictor. To account for variability in uncontrolled disturbances around the nests, we included two additional predictors. First, we counted the total number of nest visits that was the sum of the visits at the focal nest plus at all other nests with 100 meters of the focal nests during the period we studied the focal nest (number of visits henceforward). Second, we measured the distance (in m) of the focal nest from the nearest gravel road used by the vehicles of forest workers and hunters. We also added the year of the study (as a two-level factor: 2022 or 2023) and the timing of breeding (as a two-level factor: annual first or second brood) as predictors to the model. Finally, to test whether the effect of the experimental treatment depends on any of the latter four predictors, we included all four two-way interactions. Female ID was included in the model as a random factor. We also investigated whether brood ID (accounting for multiple broods per female) or the forest block (in which nests were exposed to the same type of experimental treatment) should be included as further random factors. However, adding these latter two random variables did not improve model fit and the models including them were rejected against the model including only female ID (likelihood ratio test p> 0.9 in all cases), thus we retained only female ID as random factor. Vigilance behaviour was analysed by a generalized linear mixed-effects model with binomial error distribution and logit link function. For this purpose, we transformed vigilance scores into a binary response variable. First, we calculated the median of the three vigilance scores we recorded from each 30 min video. Then we assigned the median vigilance of the parent for that sample as either low level vigilance (0; median score ≤ 1) or high level of vigilance (1; median score > 1). Beside the same fixed factors and interactions included in the model for female behaviour (see above), we also added the sex of the parent as a further predictor and its two-way interaction with experimental treatment. We included only pair ID as random factor because adding brood ID and/or forest block as further random effects did not improve model fit. Return latency of parents was analysed by a linear mixed-effects model. Latencies were logarithm-transformed. Those observations of parents when they did not return to the nest by the end of the 30 min sampling period were included with maxim latencies (1800 sec; 28 of 532 observations). The model included the same fixed factors and interactions as the model for vigilance (see above). We included both pair ID and brood ID (nested in pair ID) as random factors. Forest blocks included as a further random effect did not improve model fit hence it was omitted. To test the robustness of the results, we repeated all statistical models with excluding the broods that could be the second annual broods of unringed parents (see Supporting methods S1) where we could not control for potential pseudoreplication by pair ID. Furthermore, we repeated the analysis of return latencies using a Cox proportional hazards model with mixed effects. This latter method uses censoring for those data where the maximal return latency was assumed for birds that did not returned to the nest box until the end of the behavioural test. The predictor structure of these models was identical to those described above. All continuous predictors in the models were standardized before the analyses. See Supporting methods S4 for the R packages we used to implement the statistical models and to visualize results. 2.5 Ethical Note All procedures were in accordance with the ASAB/ABS Guidelines for the Use of Animals in Research and with Hungarian laws, licensed by the Middle Transdanubian Inspectorate for Environmental Protection, Natural Protection and Water Management (permit numbers: VE-09Z/03454-8/2018 and VE/30/00950-6/2022). 3 Results 3.1 Disturbance tolerance by females during incubation Treatments affected the probability that females stay on the nest during nest checking (Table 1A, Fig. S4A), with females in the human disturbance treatment were significantly more tolerant (i.e. stayed more frequently on the nest) than females in the no-playback control group, whereas females in the birdsong control exhibited intermediate tolerance (Fig. 1A). The effects of the playback treatments were modulated by the number of visits near the nests (Table 1A, Fig. S4A). Specifically, the tolerance of females decreased with the number of visits in the no-playback group whereas it increased in the human disturbance and birdsong treatments, with model estimates consistently suggesting highest tolerance in the human disturbance treatment (Fig. 1B). The probability of staying on the nest increased with distance to roads (Table 1A, Fig. S4A, Fig. S5A). There were also temporal changes in female behaviour: they stayed on the nest with higher probability during the second than first brood within the same year, and in 2023 than in 2022 (Fig. S5B-C). Finally, there was a marginally non-significant treatment × year interaction, suggesting the diminishing of difference between the human disturbance and birdsong control groups in 2023 (Table 1A, Fig. S5D). None of these results changed qualitatively when the annual second broods of unringed pairs were excluded (Table S1). 3.2 Disturbance tolerance by parents during the brood rearing period The vigilance behaviour of returning parents after standardized disturbances was affected by the experimental treatments: birds in the human disturbance group showed high level vigilance significantly less often than birds in the no-playback control group, with parents in the birdsong control group exhibiting an intermediate level of vigilance (Table 1B, Fig. 2, Fig. S4B). The probability of high level vigilance was higher in the first than in the second year and this temporal change was independent of experimental treatment (Table 1B, Fig. S4B, Fig. S6A). The effects of treatments on return latency of parents were modulated by the number of nest checking visits around the nest (Table 1C): return latency increased with the frequency of visits both in the no-playback and birdsong control groups, whereas it decreased in the human disturbance group (Fig. 3A), with the slope for the latter treatment being significantly different from both control treatments (Fig. S4C-D). Treatment effects were also in interactions with both brood and year effects (Table 1C, Fig. 3B-C), suggesting a decreased latency in the birdsong control during the second broods and an increased latency by birds in the human disturbance treatment in 2023 (Fig. S4C). Return latency was also related to the nests’ distance from roads, with parents of nest situated farther from roads exhibiting longer latencies (Fig. S6B). None of these results changed qualitatively when the annual second broods of unringed pairs were excluded (Table S1), or when return latencies were analysed by a mixed-effects Cox model (Table S2). Discussion In the last few decades, a large number of studies demonstrated that animals exhibit increased disturbance tolerance in anthropogenic environments, and it is widely assumed that their tolerance is causally linked to repeated exposures to the presence and activities of harmless humans (Blumstein 2016; Čapkun-Huot et al. 2024; Geffroy et al. 2020; Mikula et al. 2023; Samia et al. 2015). These results imply that both phenotypic plasticity (e.g. through learning) and rapid evolutionary processes (e.g. local adaptation through genetic or epigenetic changes) can contribute to the emergence and spread of behavioural tolerance. However, experimental inferences of the mechanisms in wild populations are generally lacking (Uchida & Blumstein 2021). Our study shows that a few weeks of disturbance simulated by playbacks can significantly increase behavioural tolerance in adult great tits. Remarkably, the estimated probability of females staying on nests during nest checking in the disturbance treatment (Fig. 1A) corresponds to the highest level of tolerance (80% staying, observed in Veszprém city) we measured in urban great tits (Vincze et al. 2021). This suggest that at least some components of behavioural tolerance can emerge by quick processes that change the behaviour of individuals. Habituation (or a habituation-like process) is a likely mechanism that explains increased tolerance in the human disturbance group. By hearing nearby humans, birds were frequently exposed to repeated (simulated) presence of non-harmful humans on their territories, which is predicted to cause habituation (Blumstein 2016; Rankin et al. 2009). This experimental situation is similar to that experienced by great tits breeding in some urban areas (e.g. in parks and suburbs). Our conclusion is in line with recent studies suggesting that plasticity, especially by habituation, may be a key mechanism behind tolerance (e.g. Uchida & Blumstein 2021), although other studies suggest the importance of additional mechanisms (e.g. Bar-Ziv et al. 2023). In our study, for example, social learning may also have promoted tolerance since both members of breeding pairs were exposed to treatments thus behavioural changes in one parent could initiate or reinforce similar changes in the other parent (Seress et al. 2017). The increased tolerance in the human disturbance group cannot be simply the result of habituation to a particular stimulus. First, we used a set of different human speech records with variable length of playbacks and silence, and playing periods were interrupted by days of non-playing periods that likely prevents habituation to any single record (Zanette et al. 2011). Second, the probability of females staying on nest was measured in a situation that typically did not involve human speech (nest checking often were conducted by a single person), thus incubating females responded to cues associated by the approach and the handling of nest box by the observer. Thus, the response of birds in this latter situation suggests a more general tolerance to the presence of humans developed during the experiment. Since playbacks were started after the birds established territories and laid eggs, habitat choice by pre-existing disturbance tolerance (Carrete & Tella 2010) is unlikely to explain the treatment effects. Another mechanism that potentially confounded our results is human shield effect (Blumstein 2016, Uchida et al. 2024): the simulated presence of people could scare away predators from the nests in the disturbance treatment resulting in, for example, reduced anti-predator vigilance by the parents. Although we did not specifically test the birds’ anti-predator responses, the number of potential predators of broods and adult great tits (e.g. woodpeckers, corvids, and birds of prey) was noted at each nest checking. These latter data do not suggest that predators were less common around the nests with disturbance treatment (Table S3), which does not support a significant human shield effect. Two tolerance measures (staying on nest, return latency) were affected by experimental treatments in interaction with the number of nest visits by researchers. Specifically, increasing number of visits was associated with increased and reduced tolerance in the human disturbance and the control groups, respectively (except birdsong control showing an intermediate trend for staying on nest). We speculate that differences in the characteristics of the human disturbance stimuli may be related to these opposite effects. Specifically, human speech playbacks may be a low intensity stimulus relative to nest visits, the latter often involving threatening actions like the close approach of nest boxes and handling of nestlings. In the disturbance treatment, birds were predominantly exposed to frequent and low intensity stimuli that is expected to promote habituation (Petrinovich 1984; Rankin et al. 2009). A high number of nest visits seems to reinforce this, which may be related to the increased (by up to 10%) encounter rate with human stimuli, or to the more frequent appearance of people around the nest making the playback treatment more similar to real disturbances. In control treatments, the birds encountered with relatively infrequent and high intensity stimuli, which does not favour habituation but may promote sensitization (Petrinovich 1984) that would explain the observed decrease in tolerance. Note, however, that stimulus characteristics can have complex effects on the behavioural outcomes of exposure to repeated stimuli (Petrinovich 1984). Sensitization in response to high level of human disturbance has repeatedly been observed (Blumstein 2014; Reimers et al. 2009; Uchida & Blumstein 2021), thus a better understanding of the mechanism and ecology of its emergence would be important and may also have significant management and conservation implications (Blumstein 2016). The distance of nests from roads predicted some behavioural proxies of tolerance independently from experimental treatments. First, females stayed less frequently on nests close to roads, suggesting sensitization. Second, parents exhibited reduced return latencies, i.e. increased tolerance, close to roads. As for the effects of nest visit (see above), these variable responses may be explained by context-dependent effects of disturbance (Petrinovich 1984, Uchida & Blumstein 2021), or may reflect the impact of other environmental factors. For example, traffic noise close to roads can obstruct the detection of cues associated with disturbance, similarly to predator cues (Petrelli et al. 2017). This would predict reduced avoidance that may contribute to the shorter return latencies by parent birds close to roads, although it cannot explain the lower probability of staying on nest by females. Alternatively, roads and associated habitat edges often have altered ecological conditions that can facilitate predator movements (Quiles & Barrientos 2024) or alter foraging conditions (Kroeger et al. 2022) ), which may have knock on effects on disturbance tolerance. The few studies that measured behavioural tolerance in relation to traffic noise found variable and species-specific responses, including sensitizing, that was in some cases partially predicted by foraging mode (Jung et al. 2020; Matyjasiak et al. 2024; Petrelli et al. 2017). Given that road density is dramatically increasing worldwide including non-urban areas, the way roads can modulate disturbance effects is an important knowledge gap deserving further studies. Our comparisons between first and second broods and between years suggest that tolerance increased during the study. Similar long-term temporal changes were reported by other studies (Arroyo et al. 2017, Uchida & Blumstein 2021). The prolonged effects of disturbance could be based on several mechanisms, for example both habituation and social learning can result in long-term behavioural changes (Bennett & Whiskin 2003; Rankin et al. 2009). The persistent effects of disturbance may also explain why birds in the birdsong treatment showed intermediate tolerance both in staying on the nest and in vigilance (Figs. 1 and 2), because at least some of the birds included in this group in the second year were exposed to disturbance treatment in the preceding year. On the other hand, the treatment × brood and treatment × year interactions for return latency cannot be interpreted as the consequences of persistent habituation since, for example, we inferred an increased latency in the disturbance treatment in the second year. One reason for the inconsistent results may be that return latency was tested during brood rearing when parents feed the nestlings, thus it may be affected by food availability that can fluctuate temporally (between first and second broods, and between the years; Seress et al. 2020; Sinkovics et al. 2023) and spatially (e.g. among forest blocks and territories; Seki & Takano 1998; Seress et al. 2025; Wilkin et al. 2009). An alternative explanation for the temporal changes could be that less tolerant birds left the study area, which may increase the average tolerance level in the population. However, we never found that ringed parents moved between forest blocks between their first and second broods or between years (see Supporting methods S2). Furthermore, in 2023 we recaptured 60.7% (17/28) of parents ringed in 2022, which is close to the figure expected by the annual survival of adult great tits in forest populations in our region (30-60%, Bukor et al. in press; see also Kirwan et al. 2024). These observations do not suggest a significant emigration of parent birds from the study area. In conclusion, our study showed that persistent human disturbance is causally linked to increased tolerance, and confirm that phenotypic plasticity is involved in the process. Since human disturbance is increasingly impacting animal populations, becoming tolerant enables populations to persist in and exploit the human-dominated environments that ultimately affects the structure and processes of ecological communities including interactions with humans (Blumstein 2016, Smith et al. 2024, Uchida et al. 2024). We suggest that playback experiments is a promising approach to tests the mechanisms leading to behavioural tolerance that can help understand current ecological changes in anthropogenic environments. Acknowledgements We thank Laura Széles, Kinga Kelemen, Tamás Judák and Balázs Erdei for their valuable help in the fieldwork. We also thank József Váradi, Ignác Korm and Sándor Gergál (Bakonyerdő Zrt.) who allowed access to the study area and helped in organizing of the work. The study was funded by the National Research, Development and Innovation Office of Hungary (grant K132490 to AL), by the HUN-REN TKI Hungarian Research Network (grant 1600707 to AL) and by the Sustainable Development and Technologies National Programme of the Hungarian Academy of Sciences (NP2022-II-6/2022). References Agnvall, B., Bélteky, J., Katajamaa, R. & Jensen, P. (2018). Is evolution of domestication driven by tameness? A selective review with focus on chickens. Appl Anim Behav Sci , 205, 227–233. Arroyo, B., Mougeot, F. & Bretagnolle, V. (2017). Individual variation in behavioural responsiveness to humans leads to differences in breeding success and long-term population phenotypic changes. Ecol Lett , 20, 317–325. Bar-Ziv, M., Sofer, A., Gorovoy, A. & Spiegel, O. (2023). Beyond simple habituation: Anthropogenic habitats influence the escape behaviour of spur-winged lapwings in response to both human and non-human threats. Journal of Animal Ecology , 92, 417–429. Bennett, G.G.Jr. & Whiskin, E.E. (2003). Socially transmitted food preferences can be used to study long-term memory in rats. Learn Behav , 2, 160–164. Blumstein, D.T. (2014). Attention, habituation, and antipredator behaviour: implications for urban birds. In: Avian Urban Ecology (ed. Gil Diego, B.H.). Oxford University Press, Oxford, Oxford, pp. 41–53. Blumstein, D.T. (2016). Habituation and sensitization: new thoughts about old ideas. Anim Behav , 120, 255–262. Bötsch, Y., Tablado, Z. & Jenni, L. (2017). Experimental evidence of human recreational disturbance effects on bird-territory establishment. Proceedings of the Royal Society B: Biological Sciences , 284. Bukor, B., Sandercock, B.K., Evans, K.L., Pipoly, I., Sándor, K., Liker, A., Seress, G. (2025) Site-specific impacts of urbanization on annual survival of a forest bird. Ecol Evol , in press (accepted) Čapkun-Huot, C., Blumstein, D.T., Garant, D., Sol, D. & Réale, D. (2024). Toward a unified framework for studying behavioural tolerance. Trends Ecol Evol , 39, 446–455. Carrete, M., Martínez-Padilla, J., Rodríguez-Martínez, S., Rebolo-Ifrán, N., Palma, A. & Tella, J.L. (2016). Heritability of fear of humans in urban and rural populations of a bird species. Sci Rep , 6: 31060. Carrete, M. & Tella, J.L. (2010). Individual consistency in flight initiation distances in burrowing owls: a new hypothesis on disturbance-induced habitat selection. Biol Lett , 6, 167–170. Chew, S.J., Vicario, D.S. & Nottebohm, F. (1996). Quantal Duration of Auditory Memories. Science (1979) , 274, 1909–1914. Frid, A. & Dill, L. (2002). Human-caused disturbance stimuli as a form of predation risk. Ecology and Society , 6:11. Geffroy, B., Sadoul, B., Putman, B.J., Berger-Tal, O., Garamszegi, L.Z., Møller, A.P., et al. (2020). Evolutionary dynamics in the anthropocene: Life history and intensity of human contact shape antipredator responses. PLoS Biol , 18(9): e3000818. Herry, C., Ferraguti, F., Singewald, N., Letzkus, J.J., Ehrlich, I. & Lüthi, A. (2010). Neuronal circuits of fear extinction. European Journal of Neuroscience , 31, 599–612. Holtmann, B., Santos, E.S.A., Lara, C.E. & Nakagawa, S. (2017). Personality-matching habitat choice, rather than behavioural plasticity, is a likely driver of a phenotype‒environment covariance. Proceedings of the Royal Society B: Biological Sciences , 284: 20170943. Jung, H., Sherrod, A., LeBreux, S., Price, J.M. & Freeberg, T.M. (2020). Traffic noise and responses to a simulated approaching avian predator in mixed-species flocks of chickadees, titmice, and nuthatches. Ethology , 126, 620–629. Kirwan, G.M., Sly, N.D., Gosler, A., Clement, P., Christie, D., Moura, N., et al. (2024). Great Tit (Parus major). In: Birds of the World (eds. Kirwan, G.M. & Sly, N.D.). Cornell Lab of Ornithology. Kluijver, H.N. (1950). Daily Routines of the Great Tit, Parus m. major L. Ardea , 1–2, 99–135. Kroeger, S.B., Hanslin, H.M., Lennartsson, T., D’Amico, M., Kollmann, J., Fischer, C., et al. (2022). Impacts of roads on bird species richness: A meta-analysis considering road types, habitats and feeding guilds. Science of the Total Environment , 812: 1514478. MacLean, S.A. & Bonter, D.N. (2013). The sound of danger: Threat sensitivity to predator vocalizations, alarm calls, and novelty in gulls. PLoS One , 8(12): e82384. Matyjasiak, P., Chacińska, P. & Książka, P. (2024). Anthropogenic noise interacts with the predation risk assessment in a free-ranging bird. Curr Zool , 70, 277–283. McIvor, G.E., Lee, V.E. & Thornton, A. (2022). Nesting jackdaws’ responses to human voices vary with local disturbance levels and the gender of the speaker. Anim Behav , 192, 119–132. Mikula, P., Tomášek, O., Romportl, D., Aikins, T.K., Avendaño, J.E., Braimoh-Azaki, B.D.A., et al. (2023). Bird tolerance to humans in open tropical ecosystems. Nat Commun , 14: 2146. Møller, A.P. (2014). Life history, predation and flight initiation distance in a migratory bird. J Evol Biol , 27, 1105–1113. Pearsons, K.S., Bennett, R.L., Fidell, S.A. (1977). Speech levels in various noise environments (Report No. EPA-600/1-77-025) . U.S. Environmental Protection Agency, Washington, DC. Petrelli, A.R., Levenhagen, M.J., Wardle, R., Barber, J.R. & Francis, C.D. (2017). First to flush: The effects of ambient noise on songbird flight initiation distances and implications for human experiences with nature. Front Ecol Evol , 5: 67. Petrinovich, L. (1984). A two-factor dual-process theory of habituation and sensitization. In: Habituation, sensitization, and behavior (eds. Peeke, H.V.S. & Petrinovich, L.). Academic Press, pp. 17–55. Quiles, P. & Barrientos, R. (2024). Interspecific interactions disrupted by roads. Biological Reviews , 99, 1121–1139. Rankin, C.H., Abrams, T., Barry, R.J., Bhatnagar, S., Clayton, D.F., Colombo, J., et al. (2009). Habituation revisited: An updated and revised description of the behavioral characteristics of habituation. Neurobiol Learn Mem , 92, 135–138. Reimers, E., Loe, L.E., Eftestøl, S., Colman, J.E. & Dahle Bjørn. (2009). Effects of Hunting on Response Behaviors of Wild Reindeer. J Wildl Manage , 73, 844–851. Samia, D.S.M., Nakagawa, S., Nomura, F., Rangel, T.F. & Blumstein, D.T. (2015). Increased tolerance to humans among disturbed wildlife. Nat Commun , 6, 1–8. Schell, C.J., Young, J.K., Lonsdorf, E. V., Santymire, R.M. & Mateo, J.M. (2018). Parental habituation to human disturbance over time reduces fear of humans in coyote offspring. Ecol Evol , 8, 12965–12980. Seki, S.-I. & Takano, H. (1998). Caterpillar abundance in the territory affects the breeding performance of great tit Parus major minor. Oecologia , 514–521. Seress, G., Sándor, K., Bókony, V., Bukor, B., Hubai, K. & Liker, A. (2025). Radio‐tracking urban breeding birds: The importance of native vegetation. Ecological Applications , 35: e3095. Seress, G., Sándor, K., Evans, K.L. & Liker, A. (2020). Food availability limits avian reproduction in the city: An experimental study on great tits Parus major. Journal of Animal Ecology , 89, 1570–1580. Seress, G., Vincze, E., Pipoly, I., Hammer, T., Papp, S., Preiszner, B., et al. (2017). Effects of capture and video‐recording on the behavior and breeding success of Great Tits in urban and forest habitats. J Field Ornithol , 88, 299–312. Sinkovics, C., Seress, G., Pipoly, I., Vincze, E. & Liker, A. (2023). Comparison of nestling diet between first and second broods of great tits Parus major in urban and forest habitats. Anim Biodivers Conserv , 46, 199–212. Smith, J.A., McDaniels, M.E., Peacor, S.D., Bolas, E.C., Cherry, M.J., Dorn, N.J., et al. (2024). Population and community consequences of perceived risk from humans in wildlife. Ecol Lett , 27: e14456. Smith, J.A., Suraci, J.P., Clinchy, M., Crawford, A., Roberts, D., Zanette, L.Y., et al. (2017). Fear of the human ‘super predator’ reduces feeding time in large carnivores. Proceedings of the Royal Society B: Biological Sciences , 284: 20170433. Sprau, P. & Dingemanse, N.J. (2017). An Approach to Distinguish between Plasticity and Non-random Distributions of Behavioral Types Along Urban Gradients in a Wild Passerine Bird. Front Ecol Evol , 5: 92. Suraci, J.P., Clinchy, M., Zanette, L.Y. & Wilmers, C.C. (2019). Fear of humans as apex predators has landscape-scale impacts from mountain lions to mice. Ecol Lett , 22, 1578–1586. Tablado, Z. & Jenni, L. (2017). Determinants of uncertainty in wildlife responses to human disturbance. Biological Reviews , 92, 216–233. Uchida, K. & Blumstein, D.T. (2021). Habituation or sensitization? Long-term responses of yellow-bellied marmots to human disturbance. Behavioral Ecology , 32, 668–678. Uchida, K., Blumstein, D.T. & Soga, M. (2024). Managing wildlife tolerance to humans for ecosystem goods and services. Trends Ecol Evol , 39, 248–257. Vincze, E., Bókony, V., Garamszegi, L.Z., Seress, G., Pipoly, I., Sinkovics, C., et al. (2021). Consistency and plasticity of risk-taking behaviour towards humans at the nest in urban and forest great tits, Parus major. Anim Behav , 179, 161–172. Vincze, E., Pipoly, I., Seress, G., Preiszner, B., Papp, S., Németh, B., et al. (2019). Great tits take greater risk toward humans and sparrowhawks in urban habitats than in forests. Ethology , 125, 686–701. Wilkin, T.A., King, L.E. & Sheldon, B.C. (2009). Habitat quality, nestling diet, and provisioning behaviour in great tits Parus major . J Avian Biol , 40, 135–145. Zanette, L.Y., Frizzelle, N.R., Clinchy, M., Peel, M.J.S., Keller, C.B., Huebner, S.E., et al. (2023). Fear of the human “super predator” pervades the South African savanna. Current Biology , 33, 4689-4696.e4. Zanette, L.Y., White, A.F., Allen, M.C. & Clinchy, M. (2011). Perceived predation risk reduces the number of offspring songbirds produce per year. Science (1979) , 334, 1398–1401. Tables and figures Table 1. The effects of experimental treatment (no-playback, birdsong, and human disturbance), uncontrolled disturbances (number of visits around the nests and distance to roads), and other predictors on three proxies of behavioural tolerance: (A) staying on the nests by females, (B) level of vigilance and (C) return latency to the nest by the parents after disturbance. The table shows the results of generalized (A, B) and linear (C) mixed models. Effects are presented as analysis of deviance tables with type-3 sums of squares, significant effects are highlighted in bold. Df χ 2 p χ 2 p χ 2 p Intercept 1 7.539 0.006 0.011 0.917 3.989 0.046 Treatment 2 10.361 0.006 6.318 0.043 5.719 0.057 No. visits within 100 m of the nest 1 6.602 0.010 0.712 0.399 3.074 0.080 Distance to road 1 4.328 0.037 2.762 0.097 3.992 0.046 Year 1 4.753 0.029 4.083 0.043 1.369 0.242 Brood 1 5.877 0.015 1.379 0.240 3.730 0.053 Sex of parent 1 - - 0.980 0.322 0.488 0.485 Treatment × No. nest checks 2 6.828 0.033 3.431 0.180 8.911 0.012 Treatment × Distance to road 2 4.420 0.110 3.101 0.212 2.387 0.303 Treatment × Year 2 5.671 0.059 4.431 0.109 6.567 0.037 Treatment × Brood 2 1.805 0.406 4.451 0.108 13.225 0.001 Treatment × Sex of parent 2 - - 0.824 0.662 3.905 0.142 Fig 1. Probability of female great tits staying on the nest during nest checking by human observers. (A) Differences between treatments. (B) The interactive effects of treatment and number of visits by the researchers within 100 m of the nests. Figures show the predicted effects of the model presented in Table 1A. Fig 2. Differences between treatment groups in the probability of high level vigilance by parent great tits after standard disturbance. Figures show the predicted effects of the model presented in Table 1B. Fig 3. Return latency of parent great tits to their nests after standard disturbance. The interactive effects of treatments (no-playback: blue, birdsong: yellow, human disturbance: red) and (A) number of visits by the researchers within 100 m of the nests, (B) brood (annual first or second), and (C) study year. Figures show the predicted effects of the model presented in Table 1C. Return latency is on standardized scale. Information & Authors Information Version history V1 Version 1 31 March 2025 Peer review timeline Published Ecology Letters Version of Record 29 Jan 2026 Published Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords anthropogenic environment disturbance tolerance habituation human disturbance learning phenotypic plasticity urbanization Authors Affiliations András Liker 0000-0001-8545-4869 [email protected] University of Pannonia View all articles by this author Csenge Sinkovics University of Pannonia View all articles by this author Krisztina Sándor Balaton Uplands National Park Directorate View all articles by this author Boglárka Bukor University of Pannonia View all articles by this author Nóra Nagy University of Veterinary Medicine Budapest View all articles by this author Levente Ódor Németh László Highschool View all articles by this author Krisztián Klucsik University of Pannonia View all articles by this author Nóra Ágh University of Pannonia View all articles by this author Metrics & Citations Metrics Article Usage 403 views 252 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation András Liker, Csenge Sinkovics, Krisztina Sándor, et al. 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