The Effects of Oral Lavender Therapy on Wounding in Chimpanzees (Pan troglodytes).

Lavender administration in humans has been shown to promote calmness without the side effects often observed with benzodiazepines. Studies in both humans and rodents have found that ingestion of oral lavender capsules resulted in significantly decreased anxiety. Additionally, mice developed an anti-conflict effect and humans increased socially inclusive behaviors. Given the safety of oral lavender oil and the observed benefits, we administered daily lavender capsules to six chimpanzees who exhibited conflict-instigating behaviors in an effort to further decrease our already low levels of wounding. We compared the total number of wounds in 25 chimpanzees housed with the six lavender-treated chimpanzees in five different social groups (1) prior to administration of daily oral lavender capsules to (2) total wounds during daily oral lavender capsule treatment. We hypothesized that lavender therapy treatment would reduce overall wounding in the social groups. Surprisingly, overall wounding was higher during the lavender treatment period (p = 0.01), yet the percentage of wounds requiring treatment significantly decreased during the lavender therapy period (36% vs. 21%, p = 0.02).

Chimpanzees (Pan troglodytes) in U.S. Zoos, Sanctuaries, and Research Facilities: A Survey-Based Comparison of Species-Typical Behaviors.

A survey was sent to zoos, research facilities, and sanctuaries which housed chimpanzees. Data collected included information about 1122 chimpanzees' age, sex, social group-size, rearing history, and enclosure. Respondents were also asked to indicate if certain behaviors had been observed in each chimpanzee over the prior two years. Species- typical behaviors (STBs) were queried, including copulation, tool-use, nest-building, and social grooming. Tool-use was reported present for 94.3% of the sample (n = 982), active social grooming for 85.7% (n = 1121), copulation for 68.3% (n = 863) and nest-building for 58.9% (n = 982). Of the subjects for whom we had data regarding all four STBs (n = 860), 45.6% were reported to engage in all four. Logistic regression analyses using forward Wald criteria were conducted to determine the best model for each STB based on the predictors of age, sex, rearing history, group-size, facility-type, and a sex-by-rearing interaction. The best model for copulation (χ2(6) = 124.62, p < 0.001) included rearing, group-size, facility-type, and the sex-by-rearing interaction. Chimpanzees were more likely to copulate if they were mother-reared, in larger groups, living in research facilities, and, if not mother-reared (NOTMR), more likely to copulate if they were female. The best model for tool-use retained the predictors of age category, facility-type, and sex-by-rearing (χ2(5) = 55.78, p < 0.001). Chimpanzees were more likely to use tools if they were adult, living in research facilities, and if NOTMR, were female. The best model for nest-building included facility-type and rearing (χ2(3) = 205.71, p < 0.001). Chimpanzees were more likely to build nests if they were MR and if they were living in zoos or in sanctuaries. The best model for active social grooming retained the predictors of age, sex, rearing, and type of facility (χ2(6) = 102.15, p < 0.001). Chimpanzees were more likely to engage in active social grooming if they were immature, female, mother-reared, and living in zoos. This research provides a basic behavioral profile for many chimpanzees living under human care in the United States and allows us to determine potential methods for improving the welfare of these and future chimpanzees in this population.

Innovative multi-material tool use in the pant-hoot display of a chimpanzee.

'Pant-hoot displays' are a species-typical, multi-modal communicative behaviour in chimpanzees in which pant-hoot vocalisations are combined with varied behavioural displays. In both captivity and the wild, individuals commonly incorporate striking or throwing elements of their environment into these displays. In this case study, we present five videos of an unenculturated, captive, adult male chimpanzee combining a large rubber feeding tub with excelsior (wood wool) in a multi-step process, which was then integrated into the subject's pant-hoot displays as a percussive tool or 'instrument'. During the construction process, the subject demonstrated an understanding of the relevant properties of these materials, 'repairing' the tub to be a more functional drum when necessary. We supplement these videos with a survey of care staff from the study site for additional detail and context. Although care must be taken in generalising data from a single individual, the behaviour reported here hints at three intriguing features of chimpanzee communicative cognition: (1) it suggests a degree of voluntary control over vocal production, (2) it is a so-far unique example of compound tool innovation and use in communicative behaviour and (3) it may represent an example of forward planning in communicative behaviour. Each of these would represent hitherto undocumented dimensions of flexibility in chimpanzee communication, mapping fertile ground for future research.

Playbacks of food-associated calls attract chimpanzees towards known food patches in a captive setting.

Food-associated calls have received much research attention due to their potential to refer to discovered food in a word-like manner. Studies have found that in many species, food-associated calls attract receivers to the food patch, suggesting these calls play roles in food sharing, cooperation and competition. Additionally, in various species, these calls play a role that has received much less attention: mediating social interactions among foragers that are already nearby or within the food patch, independently of whether they attract outside foragers. In order to increase understanding of the function of the chimpanzee (Pan troglodytes) food-associated rough grunt, we conducted captive playback studies testing whether rough grunt playbacks attract, repel or have no effect on the proximity of foragers already familiarized with the presence of food. We tested how acoustic playbacks of rough grunts (or control calls) from one of two known, identical feeding sites affected receivers' approach and feeding behaviors. More often than expected, participants first approached the feeding site from which rough grunts, but not control calls, were broadcast. However, neither condition increased the likelihood that participants fed first from a given site. Our results support the hypothesis that rough grunts elicit an approach response in receivers, while providing no evidence that they repel. In addition, our study provides evidence that receivers may approach rough grunts even if they do not intend to feed. We discuss the information rough grunts may convey to receivers beyond information about discovered food and the potential benefits signalers may gain from this calling behavior.

Reply to comment on "Nonadjacent dependency processing in monkeys, apes, and humans".

Rawski et al. revisit our recent findings suggesting the latent ability to process nonadjacent dependencies ("Non-ADs") in monkeys and apes. Specifically, the authors question the relevance of our findings for the evolution of human syntax. We argue that (i) these conclusions hinge upon an assumption that language processing is necessarily hierarchical, which remains an open question, and (ii) our goal was to probe the foundational cognitive mechanisms facilitating the processing of syntactic Non-ADs-namely, the ability to recognize predictive relationships in the input.

Behavioral Management is a Key Component of Ethical Research.

Behavioral management programs aim to enhance the welfare of animal subjects that participate in research, thereby enhancing our ability to conduct ethical research projects. Socialization strategies, environmental enrichment techniques, opportunities for subjects to voluntarily participate in research procedures, and the provision of Functionally Appropriate Captive Environments are 4 major components of most behavioral management programs. The appropriate implementation of behavioral management programs should provide animals with opportunities to engage in species-typical activity patterns, contributing to valid and reliable animal models that require the smallest number of subjects to achieve meaningful results. The role that socialization strategies, environmental enrichment techniques, and positive reinforcement training can play in maintaining and enhancing welfare through the stimulation of species-typical behavior and the prevention of abnormal behavior is discussed. The value of empirically assessing the effects of behavioral management techniques is emphasized. Additionally, the necessity of adjusting the relative prioritization of needs related to the convenience of human caregivers and the animals themselves is addressed. For the purposes of this discussion, research projects are considered to be ethical if they (1) involve animals with high welfare, (2) provide data that are reliable and valid, (3) involve appropriate numbers of subjects, and (4) involve animals that are appropriate models to test meaningful hypotheses.

Unpacking chimpanzee (Pan troglodytes) patch use: Do individuals respond to food patches as predicted by the marginal value theorem?

The marginal value theorem is an optimal foraging model that predicts how efficient foragers should respond to both their ecological and social environments when foraging in food patches, and it has strongly influenced hypotheses for primate behavior. Nevertheless, experimental tests of the marginal value theorem have been rare in primates and observational studies have provided conflicting support. As a step towards filling this gap, we test whether the foraging decisions of captive chimpanzees (Pan troglodytes) adhere to the assumptions and qualitative predictions of the marginal value theorem. We presented 12 adult chimpanzees with a two-patch foraging environment consisting of both low-quality (i.e., low-food density) and high-quality (i.e., high-food density) patches and examined the effect of patch quality on their search behavior, foraging duration, marginal capture rate, and its proxy measures: giving-up density and giving-up time. Chimpanzees foraged longer in high-quality patches, as predicted. In contrast to predictions, they did not depress high-quality patches as thoroughly as low-quality patches. Furthermore, since chimpanzees searched in a manner that fell between systematic and random, their intake rates did not decline at a steady rate over time, especially in high-quality patches, violating an assumption of the marginal value theorem. Our study provides evidence that chimpanzees are sensitive to their rate of energy intake and that their foraging durations correlate with patch quality, supporting many assumptions underlying primate foraging and social behavior. However, our results question whether the marginal value theorem is a constructive model of chimpanzee foraging behavior, and we suggest a Bayesian foraging framework (i.e., combining past foraging experiences with current patch sampling information) as a potential alternative. More work is needed to build an understanding of the proximate mechanisms underlying primate foraging decisions, especially in more complex socioecological environments.

Nonadjacent dependency processing in monkeys, apes, and humans.

The ability to track syntactic relationships between words, particularly over distances ("nonadjacent dependencies"), is a critical faculty underpinning human language, although its evolutionary origins remain poorly understood. While some monkey species are reported to process auditory nonadjacent dependencies, comparative data from apes are missing, complicating inferences regarding shared ancestry. Here, we examined nonadjacent dependency processing in common marmosets, chimpanzees, and humans using "artificial grammars": strings of arbitrary acoustic stimuli composed of adjacent (nonhumans) or nonadjacent (all species) dependencies. Individuals from each species (i) generalized the grammars to novel stimuli and (ii) detected grammatical violations, indicating that they processed the dependencies between constituent elements. Furthermore, there was no difference between marmosets and chimpanzees in their sensitivity to nonadjacent dependencies. These notable similarities between monkeys, apes, and humans indicate that nonadjacent dependency processing, a crucial cognitive facilitator of language, is an ancestral trait that evolved at least ~40 million years before language itself.

Validation and utility of a body condition scoring system for chimpanzees (Pan troglodytes).

Obesity is a problem in captive chimpanzee colonies that can lead to increased risk for disease; therefore, implementation of effective weight management strategies is imperative. To properly implement a weight management program, captive managers should be able to noninvasively identify and assess overweight or obese individuals. Traditional means of categorizing obese individuals involve sedating the animals to obtain body weights or skin fold measurements. The current study aimed to validate a noninvasive, subjective body condition score (BCS) system for captive chimpanzees. The system utilizes a 10-point scale, with one rated as "emaciated," five as "normal," and 10 as "extremely obese." Between 2013 and 2014, 158 chimpanzees were weighed and scored using this system (a) while sedated and (b) while awake in their social group within 1-3 days of sedation ("In-group" ratings). We found high inter-rater reliability between In-group raters, as well as between sedated and In-group scores. BCSs, which require observation only, were significantly positively correlated with weight (an objective measure of obesity often requiring anesthetization), supporting the scale's validity. The BCS system identified 36 individuals as "overweight," while the use of weights alone identified only 26 individuals as "overweight." Furthermore, the BCS system was able to classify individuals of the same sex and weight as having different BCSs, ranging from normal to overweight. Lastly, using focal animal behavioral observations from 2016 to 2018 (N = 120), we found that In-group BCS predicted individual levels of inactive behavior more than 2 years later, demonstrating the predictive validity of the scale. These results illustrate the utility of the BCS system as a noninvasive, reliable, and valid technique that may be more sensitive than traditional methods in identifying and quantifying obesity in chimpanzees. This system can be a useful tool for captive managers to monitor and manage the weight of chimpanzees and other nonhuman primates.

The implementation and initial evaluation of a physical therapy program for captive chimpanzees (Pan troglodytes).

Due to advances in captive nonhuman primate (NHP) medical care, the number of geriatric chimpanzees (≥35-years old) is growing. With old age comes a variety of physical conditions, including arthritis, stroke, and mobility impairments. Programs aimed at enhancing the welfare of geriatric chimpanzees are now quite common, but there are few published empirical evaluations of the efficacy of such programs. The current study aimed to create, implement, and evaluate the effects of participation in a physical therapy (PT) program on physical health, mobility, welfare, and behavior. Nine chimpanzees with mobility impairments participated in personalized PT routines (using positive reinforcement training) twice per week for 5 months. Additionally, nine control chimpanzees (non-mobility-impaired, matched with PT chimpanzees on age and gender) participated in body exam behavior sessions (also using positive reinforcement training) twice per week. All chimpanzees were rated on 14 health, well-being, and behavior items, as well as level of mobility throughout the PT program. Chimpanzees that participated in the PT program showed significant increases in ratings of physical health, well-being, and activity levels across phases of the program. Furthermore, compared to control chimpanzees, PT chimpanzees showed significant increases in ratings of ease of movement. Because raters were not blind to physical therapy treatment, our results represent an initial evaluation of the program that may suggest that participation in the PT program has physical, behavioral, and welfare benefits. Assessments of novel geriatric-focused care strategies and programs are essential to further enhance the welfare of the captive chimpanzee population, which is currently comprised of many geriatric animals, whose proportion of the captive population will only increase.

Sex differences in longitudinal personality stability in chimpanzees.

Personality factors analogous to the Big Five observed in humans are present in the great apes. However, few studies have examined the long-term stability of great ape personality, particularly using factor-based personality instruments. Here, we assessed overall group, and individual-level, stability of chimpanzee personality by collecting ratings for chimpanzees (N = 50) and comparing them with ratings collected approximately 10 years previously, using the same personality scale. The overall mean scores of three of the six factors differed across the two time points. Sex differences in personality were also observed, with overall sex differences found for three traits, and males and females showing different trajectories for two further traits over the 10 year period. Regardless of sex, rank-order stability analysis revealed strong stability for dominance; individuals who were dominant at the first time point were also dominant 10 years later. The other personality factors exhibited poor to moderate rank-order stability, indicating that individuals were variable in their rank-position consistency over time. As many studies assessing chimpanzee cognition rely on personality data collected several years prior to testing, these data highlight the importance of collecting current personality data when correlating them with cognitive performance.

Differences in Behavior Between Elderly and Nonelderly Captive Chimpanzees and the Effects of the Social Environment.

The population of NIH-owned or NIH-supported captive research chimpanzees is quickly becoming aged, and the 1998 NIH breeding moratorium has resulted in a skewed age distribution. As such, behavioral management programs aimed at refining the care of an aging captive chimpanzee population have become increasingly important. However, little research exists that addresses the ways in which captive chimpanzee behavior differs as a function of the interaction of age and aspects of the captive environment. We examined overall differences in behavior between elderly (35 y and older) and nonelderly (younger than 35 y) captive chimpanzees. Elderly chimpanzees exhibited significantly more rough scratching (a behavioral indicator of anxiety) and inactivity, less behavioral diversity, and less affiliation than their nonelderly counterparts. We also assessed whether elderly chimpanzee behavior and wounding rates differed as a function of housing in geriatric (group average age, 35 y or older) or nongeriatric (group average age, younger than 35 y) groups. In our program, geriatric social groups were characterized by smaller group size, more females within the group, and higher levels of individual mobility impairment compared with nongeriatric groups. Furthermore, elderly chimpanzees housed in geriatric groups displayed significantly increased rough scratching, decreased locomotion and submission than nongeriatric animals but no difference in wounding. These findings suggest that housing elderly chimpanzees in nongeriatric groups may be beneficial, given that doing so may stimulate locomotion. However, the establishment and maintenance of geriatric groups may be unavoidable as the demographics of the population of captive former research chimpanzees continues to age. Therefore, refinements to captive geriatric care strategies for chimpanzees should focus on methods of evaluating and enhancing functionally appropriate captive environments within geriatric groups.

Chimpanzees Rarely Settle on Consistent Patterns of Play in the Hawk Dove, Assurance, and Prisoner's Dilemma Games, in a Token Exchange Task.

Games derived from experimental economics can be used to directly compare decision-making behavior across primate species, including humans. For example, the use of coordination games, such as the Assurance game, has shown that a variety of primate species can coordinate; however, the mechanism by which they do so appears to differ across species. Recently, these games have been extended to explore anti-coordination and cooperation in monkeys, with evidence that they play the Nash equilibria in sequential games in these other contexts. In the current paper, we use the same methods to explore chimpanzees' behavior in the Assurance Game; an anti-coordination game, the Hawk Dove game; and a cooperation game with a temptation to defect, the Prisoner's Dilemma game. We predicted that they would consistently play the Nash equilibria, as do the monkeys, and that, as in previous work, the subjects' level of experience with cognitive experiments would impact performance. Surprisingly, few of our pairs consistently played the same outcome (i.e., no statistically significant preferences), although those who did showed evidence consistent with Nash equilibria play, the same pattern seen more consistently in the monkeys. We consider reasons for their inconsistent performance; for instance, perhaps it was due to lack of interest in a task that rewarded them almost every trial no matter what option they chose, although this does not explain why they were inconsistent when the monkeys were not. A second goal of our study was to ascertain the effects of exogenous oxytocin in their decision making in one population. In line with recent work showing complex effects of oxytocin on social behavior, we found no effect on subjects' outcomes. We consider possible explanations for this as well.

Survey of Behavioral Indices of Welfare in Research Chimpanzees (Pan troglodytes) in the United States.

Chimpanzees demand specialized housing and care and the highest degree of attention to animal welfare. The current project used a survey method to collate information on chimpanzee housing and behavioral indices of welfare across all 6 of the chimpanzee research facilities in the United States. Data were compiled on 701 chimpanzees ranging from 2 to 62 y old (mean age, 26.0 y). All chimpanzees except for one were socially housed; the median group size was 7 animals, and group sizes ranged from 1 to 14. All of the subjects had access to outdoor spaces each day. Daily access to a natural substrate in the chimpanzee's enclosure was available for 63.8% of the subjects. Overall, 94.1% of the chimpanzees used tools to acquire food, 48.1% built nests, 75.8% copulated, and 83.3% initiated grooming bouts. The following atypical behaviors were reported most often: rocking (13.0%), coprophagy (10.0%), and stereotyped behaviors other than rocking (9.4%). There was widespread evi- dence of positive animal training techniques, with nearly all (97.7%) subjects reported to generally voluntarily cooperate with shifting in their enclosure, and 72.2% were reported to present for an injection of anesthetic. We include some comparison between these findings and data describing zoo-housed chimpanzees. In addition, we discuss survey findings in reference to recommendations made by the NIH Working Group on the Use of Chimpanzees in NIH-supported Research. The current survey assessed a larger sample of chimpanzees living under human care than has been published previously. This broad analysis can help to guide future improvements in behavioral management to address behavioral problems or deficits.

Responses to Economic Games of Cooperation and Conflict in Squirrel Monkeys (Saimiri boliviensis).

Games from experimental economics have provided insights into the evolutionary roots of social decision making in primates and other species. Multiple primate species' abilities to cooperate, coordinate and anti-coordinate have been tested utilizing variants of these simple games. Past research, however, has focused on species known to cooperate and coordinate in the wild. To begin to address the degree to which cooperation and coordination may be a general ability that manifests in specific contexts, the present study assessed the decisions of squirrel monkeys (Saimiri boliviensis; N = 10), a species not known for their cooperative behavior in these games. Pairs of monkeys were presented with the Assurance Game (a coordination game), the Hawk-Dove Game (an anti-coordination game) and the Prisoner's Dilemma (a cooperation game with a temptation to defect). We then compared squirrel monkeys' performance to existing data on capuchin monkeys (Sapajus [Cebus] apella), a closely related species that routinely cooperates, to determine what, if any, differences in decision making emerged. Some pairs of both species found the payoff-dominant Nash Equilibrium (NE) in the coordination game, but failed to find the NE in subsequent games. Our results suggest that, like capuchins, squirrel monkeys coordinate their behavior with others, suggesting that such mutual outcomes occur in at least some contexts, even in species that do not routinely cooperate.

Behavioral conservatism is linked to complexity of behavior in chimpanzees (Pan troglodytes): Implications for cognition and cumulative culture.

Cumulative culture is rare, if not altogether absent in nonhuman species. At the foundation of cumulative learning is the ability to modify, relinquish, or build upon previous behaviors flexibly to make them more productive or efficient. Within the primate literature, a failure to optimize solutions in this way is often proposed to derive from low-fidelity copying of witnessed behaviors, suboptimal social learning heuristics, or a lack of relevant sociocognitive adaptations. However, humans can also be markedly inflexible in their behaviors, perseverating with, or becoming fixated on, outdated or inappropriate responses. Humans show differential patterns of flexibility as a function of cognitive load, exhibiting difficulties with inhibiting suboptimal behaviors when there are high demands on working memory. We present a series of studies on captive chimpanzees that indicate that behavioral conservatism in apes may be underlain by similar constraints: Chimpanzees showed relatively little conservatism when behavioral optimization involved the inhibition of a well-established but simple solution, or the addition of a simple modification to a well-established but complex solution. In contrast, when behavioral optimization involved the inhibition of a well-established but complex solution, chimpanzees showed evidence of conservatism. We propose that conservatism is linked to behavioral complexity, potentially mediated by cognitive resource availability, and may be an important factor in the evolution of cumulative culture. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Chimpanzees demonstrate individual differences in social information use.

Studies of transmission biases in social learning have greatly informed our understanding of how behaviour patterns may diffuse through animal populations, yet within-species inter-individual variation in social information use has received little attention and remains poorly understood. We have addressed this question by examining individual performances across multiple experiments with the same population of primates. We compiled a dataset spanning 16 social learning studies (26 experimental conditions) carried out at the same study site over a 12-year period, incorporating a total of 167 chimpanzees. We applied a binary scoring system to code each participant's performance in each study according to whether they demonstrated evidence of using social information from conspecifics to solve the experimental task or not (Social Information Score-'SIS'). Bayesian binomial mixed effects models were then used to estimate the extent to which individual differences influenced SIS, together with any effects of sex, rearing history, age, prior involvement in research and task type on SIS. An estimate of repeatability found that approximately half of the variance in SIS was accounted for by individual identity, indicating that individual differences play a critical role in the social learning behaviour of chimpanzees. According to the model that best fit the data, females were, depending on their rearing history, 15-24% more likely to use social information to solve experimental tasks than males. However, there was no strong evidence of an effect of age or research experience, and pedigree records indicated that SIS was not a strongly heritable trait. Our study offers a novel, transferable method for the study of individual differences in social learning.

Chimpanzees prioritise social information over pre-existing behaviours in a group context but not in dyads.

How animal communities arrive at homogeneous behavioural preferences is a central question for studies of cultural evolution. Here, we investigated whether chimpanzees (Pan troglodytes) would relinquish a pre-existing behaviour to adopt an alternative demonstrated by an overwhelming majority of group mates; in other words, whether chimpanzees behave in a conformist manner. In each of five groups of chimpanzees (N = 37), one individual was trained on one method of opening a two-action puzzle box to obtain food, while the remaining individuals learned the alternative method. Over 5 h of open access to the apparatus in a group context, it was found that 4/5 'minority' individuals explored the majority method and three of these used this new method in the majority of trials. Those that switched did so after observing only a small subset of their group, thereby not matching conventional definitions of conformity. In a further 'Dyad' condition, six pairs of chimpanzees were trained on alternative methods and then given access to the task together. Only one of these individuals ever switched method. The number of observations that individuals in the minority and Dyad individuals made of their untrained method was not found to influence whether or not they themselves switched to use it. In a final 'Asocial' condition, individuals (N = 10) did not receive social information and did not deviate from their first-learned method. We argue that these results demonstrate an important influence of social context upon prioritisation of social information over pre-existing methods, which can result in group homogeneity of behaviour.

Testing differential use of payoff-biased social learning strategies in children and chimpanzees.

Various non-human animal species have been shown to exhibit behavioural traditions. Importantly, this research has been guided by what we know of human culture, and the question of whether animal cultures may be homologous or analogous to our own culture. In this paper, we assess whether models of human cultural transmission are relevant to understanding biological fundamentals by investigating whether accounts of human payoff-biased social learning are relevant to chimpanzees (Pan troglodytes). We submitted 4- and 5-year-old children (N = 90) and captive chimpanzees (N = 69) to a token-reward exchange task. The results revealed different forms of payoff-biased learning across species and contexts. Specifically, following personal and social exposure to different tokens, children's exchange behaviour was consistent with proportional imitation, where choice is affected by both prior personally acquired and socially demonstrated token-reward information. However, when the socially derived information regarding token value was novel, children's behaviour was consistent with proportional observation; paying attention to socially derived information and ignoring their prior personal experience. By contrast, chimpanzees' token choice was governed by their own prior experience only, with no effect of social demonstration on token choice, conforming to proportional reservation. We also find evidence for individual- and group-level differences in behaviour in both species. Despite the difference in payoff strategies used, both chimpanzees and children adopted beneficial traits when available. However, the strategies of the children are expected to be the most beneficial in promoting flexible behaviour by enabling existing behaviours to be updated or replaced with new and often superior ones.

Lack of conformity to new local dietary preferences in migrating captive chimpanzees.

Conformity to the behavioural preferences of others can have powerful effects on intragroup behavioural homogeneity in humans, but evidence in animals remains minimal. In this study, we took advantage of circumstances in which individuals or pairs of captive chimpanzees, Pan troglodytes, were 'migrated' between groups, to investigate whether immigrants would conform to a new dietary population preference experienced in the group they entered, an effect suggested by recent fieldwork. Such 'migratory-minority' chimpanzees were trained to avoid one of two differently coloured foods made unpalatable, before 'migrating' to, and then observing, a 'local-majority' group consume a different food colour. Both migratory-minority and local-majority chimpanzees displayed social learning, spending significantly more time consuming the previously unpalatable, but instead now edible, food, than did control chimpanzees who did not see immigrants eat this food, nor emigrate themselves. However, following the migration of migratory-minority chimpanzees, these control individuals and the local-majority chimpanzees tended to rely primarily upon personal information, consuming first the food they had earlier learned was palatable before sampling the alternative. Thus, chimpanzees did not engage in conformity in the context we tested; instead seeing others eat a previously unpalatable food led to socially learned and adaptive re-exploration of this now-safe option in both minority and majority participants.