Does group size matter? Captive chimpanzee (Pan troglodytes) behavior as a function of group size and composition

Locomotion as a Measure of Well-Being in Captive Chimpanzees (Pan troglodytes)

Locomotion in non-human primates, including walking, climbing, and brachiating among other types of movement (but not pacing), is a species-typical behavior that varies with age, social housing conditions, and environmental factors (e.g., season, food availability, physical housing conditions). Given that captive primates are typically observed to engage in lower levels of locomotor behaviors than their wild counterparts, increases in locomotion are generally considered to be indicative of improved welfare in captivity. However, increases in locomotion do not always occur with improvements in welfare, and sometimes occur under conditions of negative arousal. The use of time spent in locomotion as a welfare indicator in studies of well-being is relatively limited. We conducted focal animal observations on 120 captive chimpanzees across a series of studies and found higher percentages of time spent in locomotion (1) upon transfer to a new enclosure type, (2) in larger groups with wider within-group age ranges, and fewer males, and (3) with participation in an experimental medication choice paradigm. We also found that, among geriatric chimpanzees, those housed in nongeriatric groups exhibited more locomotion than those living in geriatric groups. Lastly, locomotion was significantly negatively correlated with several indicators of poor welfare and significantly positively correlated with behavioral diversity, one indicator of positive welfare. Overall, the increases in time spent in locomotion observed in these studies were part of an overall behavioral pattern indicative of enhanced welfare, suggesting that an increase in time spent in locomotion itself may be an indicator of enhanced welfare. As such, we suggest that levels of locomotion, which are typically assessed in most behavioral experiments, may be used more explicitly as indicators of welfare in chimpanzees.

Long-Term Assessment of Captive Chimpanzees: Influence of Social Group Composition, Seasonality and Biographic Background

Wild chimpanzees (Pan troglodytes) live in flexible fission-fusion societies with frequent changes in both group size and composition. These changes depend mostly on resource availability and individual social preferences yet in captivity are determined by housing organizations. During a period of seven years, we observed a group of sanctuary chimpanzees, focusing on how they adapted to changes in the group composition over time. Using linear mixed models (LMMs), factors such as group size, sex ratio, seasonality, and the individuals' sex and origin (wild caught vs. captive born) were considered in order to evaluate the impact on the chimpanzees' activity levels, the occurrence of undesired behaviors (abnormal and self-directed behaviors) and the social grooming networks. Our results indicate that the activity levels and the occurrence of undesired behaviors were impacted by changes in group composition and the individuals' biographic background. The colder season was marked by higher levels of activity and more time spent grooming. Moreover, it was the individuals' origin but not changes in group composition that affected social grooming, with wild-caught chimpanzees grooming far less frequently. Long-term observations are essential to evaluate, predict and detect potential benefits and/or issues of housing conditions while considering the social and physical environment.

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.

Aggressive, Submissive, and Affiliative Behavior in Sanctuary Chimpanzees (Pan Troglodytes) During Social Integration

Chimp Haven is a sanctuary for chimpanzees being retired from biomedical research and from facilities that can no longer care for them. Chimpanzees often live in smaller groups in captive settings; however, Chimp Haven integrates them into larger, more species-typical groups. Social integrations, the process of introducing unfamiliar chimpanzees to one another, are often complex in terms of logistics and can be stressful due to the territorial nature of the animals, reduced space in captivity, and the fact that these situations are engineered by humans. From 2005 to 2015, Chimp Haven conducted 225 social integrations including 282 chimpanzees (male: n = 135; female: n = 147). Each integration involved 2 to 26 chimpanzees (mean = 9) and their age ranged from < one year old to 59 years old (mean = 30). We collected data ad libitum during the first 60 min after doors were opened between unfamiliar chimpanzees. The chimpanzees’ affiliative, aggressive, and submissive behaviors were examined, comparing the subject’s sex, rearing history, location/enclosure type, and group size impacts on these behaviors. The subject’s sex, location, and group size were associated with the frequency of affiliative behaviors observed during social integration. All variables except for group size were associated with the frequency of aggressive behavior. The frequency of submissive behavior differed based on the subject’s sex, rearing history, and group size. We were unable to make comparisons between successful and unsuccessful integrations, as most of these integrations were successful.

A 25-Year Retrospective Review of Mortality in Chimpanzees (Pan troglodytes) in Accredited U.S. Zoos from a Management and Welfare Perspective

Understanding causes of death allows adjustment of health management strategies for animals in managed care. From 224 documented chimpanzee deaths occurring from 1995 to 2019 in 42 accredited U.S. zoos, post-mortem records and necropsy reports were analyzed for the primary cause of death, which were available for 214 individuals. In total, 37 cases of stillbirth and neonatal deaths were assessed (16.5%); however, the focus was otherwise placed on the remaining 177 cases in which the death occurred in individuals aged greater than 1 month. There were no sex-related differences in etiology; however, age variation in the cause of death was statistically significant (p < 0.001). Elderly (35 years and older) chimpanzees tended to die of intrinsic, often degenerative, etiologies, whereas infants, juveniles, and adolescents (less than 15 years) were more likely to be involved in fatal trauma. Overall, there were 27 deaths (15.3% of all post-neonatal deaths) related to trauma and 13 of these were directly or indirectly related to conspecific aggression. Understanding causes of mortality and the interrelation with management can benefit managed populations of chimpanzees.

Behavioural Development of Three Former Pet Chimpanzees a Decade after Arrival at the MONA Sanctuary

Chimpanzees used as pets and in the entertainment industry endure detrimental living conditions from early infancy onwards. The preferred option for ending their existence as pet or circus chimpanzees is their rescue and transfer to a primate sanctuary that will provide them with optimal living and social conditions, so that they can thrive. In this case study, we had the rare opportunity to compare the activity budgets of three chimpanzees from their time as pets in 2004 to their time living at the MONA sanctuary in 2020, after almost a decade in the centre. We found their behaviour patterns changed in accordance with the sanctuaries' rehabilitation objectives. Resting periods increased considerably while vigilance simultaneously declined sharply. Moreover, the chimpanzees' social competence increased as allogrooming became the predominant social behaviour, and agonistic interactions diminished even though they were living within a larger social group at the sanctuary. All three chimpanzees expanded their allogrooming and proximity networks at the sanctuary, which included new group members, but they maintained the closest relationships to those conspecifics who they were rescued with. In conclusion, these findings suggest that the sanctuary environment and social group setting made it possible for these three chimpanzees to improve their social competence and increase their well-being over time.

Are conspecific social videos rewarding to chimpanzees (Pan troglodytes)? A test of the social motivation theory

Many claim that social stimuli are rewarding to primates, but few, if any, studies have explicitly demonstrated their reward value. Here, we examined whether chimpanzees would produce overt responses for the opportunity to view conspecific social, compared to dynamic (video: Experiment 1) and static (picture: Experiment 2) control content. We also explored the relationships between variation in social reward and social behavior and cognition. We provided captive chimpanzees with access to a touchscreen during four, one-hour sessions (two 'conspecific social' and two 'control'). The sessions consisted of ten, 15-second videos (or pictures in Experiment 2) of either chimpanzees engaging in a variety of behaviors (social condition) or vehicles, humans, or other animals engaged in some activity (control condition). For each chimpanzee, we recorded the number of responses to the touchscreen and the frequency of watching the stimuli. Independent t-tests revealed no sex or rearing differences in touching and watching the social or control videos (p>0.05). Repeated measures ANOVAs showed chimpanzees touched and watched the screen significantly more often during the social compared to control video sessions. Furthermore, although chimpanzees did not touch the screen more often during social than control picture sessions in Experiment 2, they did watch the screen more often. Additionally, chimpanzees that previously performed better on a task of social cognition and engaged in more affiliative behavior watched a higher percentage of social videos during the touchscreen task. These results are consistent with the social motivation theory, and indicate social stimuli are intrinsically rewarding, as chimpanzees made more overt responses for the opportunity to view conspecific social, compared to control, content.

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.

Comparative survival analyses among captive chimpanzees (Pan troglodytes) in America and Japan

Detailed, long-term datasets on the life histories of long-lived species such as great apes are necessary to understand their survival patterns but are relatively rare. Such information requires prolonged and consistent record-keeping over many generations, so for chimpanzees (Pan troglodytes), this equates to many decades of input. As life history variables can be altered by differences in environmental influences (whether natural or artificial), there is substantial value to being able to compare across populations. Here, we present the first comparative analysis of life history data for two ex situ chimpanzee populations residing in North America (1975–2020; n = 730) and Japan (1980–2020; n = 660). Overall, survival patterns were similar between regions, and the median life expectancy from birth is estimated at 35.7 (95% CI = [32.4–40.0]) years for females and 30.1 (27.3–34.3) years for males across both populations. Females who survive to their first birthday are estimated to survive 42.4 (40.0–46.3) years and males 35.5 (32.6–38.0) years. We found that birth type (wild-born or captive-born) did not influence survival patterns in either population, but there were differential effects of sex on longevity. In the America population, males had higher mortality rates than females, whereas in the Japan population we found no differences between the sexes. First year mortality did not differ between populations for males (18–20%), but for females it was lower in America (15%) compared to Japan (25%). Survival patterns of chimpanzees in the present study will be useful for future investigation into potential causes of regional differences and cross-species comparisons.

Human caregivers are integrated social partners for captive chimpanzees

In a captive environment, it is challenging to ensure the highest level of social and psychological well-being for species with naturally complex social organizations and structures. There is a growing need to meet the social requirements for individuals of these species, especially chimpanzees, housed in zoos, sanctuaries, rehabilitation centers, and laboratories. Complex social interactions and broader social structures can be aptly described via social network analysis. We expand on the literature regarding captive chimpanzee social networks, but uniquely consider their human caregivers as potential social partners. We observed the social interactions between one group of seven chimpanzees (Pan troglodytes) and their caregivers in six behavioral contexts (nearest neighbor, play, aggression, grooming, grooming solicitation, and social vigilance) at Chimpanzee Sanctuary Northwest (USA). By constructing multiple chimpanzee and chimpanzee-caregiver social networks, our results indicate that caregivers are integrated partners in this group's social structure. Additionally, we observed that the type and strength of chimpanzee-caregiver relationships varied between the chimpanzees. These results support the notion that caregivers offer additional opportunities (i.e., beyond those with conspecifics) for captive chimpanzees to construct and maintain meaningful social relationships. Our results show that considerations of captive primate social dynamics should include caregivers as potentially important social partners. Our results also highlight the importance of evaluating individual chimpanzee characteristics when developing philosophies of care and adopting husbandry practices that offer fulfilling social niches. Our findings bear influence on contemporary discussions of interspecies social relationships, captive welfare, health, translocation, and husbandry protocols for captive chimpanzees and other nonhuman primates.

Effects of personality and rearing-history on the welfare of captive Asiatic lions (Panthera leo persica)

Background

The long-term success of ex-situ conservation programmes depends on species-appropriate husbandry and enrichment practices complemented by an accurate welfare assessment protocol. Zoos and conservation breeding programmes should employ a bottom-up approach to account for intraspecific variations in measures of animal welfare. We studied 35 (14:21) captive Asiatic lions in Sakkarbaug Zoological Garden, Junagadh, India to understand the implications of individual variations on welfare measures. We categorized the subjects based on personality traits (bold or shy), rearing history (wild-rescued or captive-raised), sex, and social-grouping. We explored the association of these categorical variables on welfare indices such as behavioural diversity, latency to approach novel objects, enclosure usage and aberrant repetitive behaviours. Further, we assessed the inter-relationships between different behavioural measures of welfare.

Results

Our results show that intraspecific variations based on rearing-history and personality traits are significantly associated with the welfare states of captive Asiatic lions. Asiatic lions with bold personality traits (M = 0.50, SD = 0.12, N = 21) and those raised in captivity (M = 0.47, SD = 0.12, N = 16) used enclosure space more homogenously compared to shy (M = 0.71, SD = 0.15, N = 14) and wild-rescued (M = 0.67, SD = 0.15, N = 19) animals. Behaviour diversity was significantly higher in captive-raised (M = 1.26, SD = 0.3, N = 16) and bold (M = 1.23, SD = 0.26, N = 21) subjects compared to wild-rescued (M = 0.83, SD = 0.35, N = 19) and shy (M = 0.73, SD = 0.34, N = 14) individuals. Aberrant repetitive behaviours (stereotypy) were significantly lower in bold (M = 7.01, SD = 4, N = 21) and captive-raised (M = 7.74, SD = 5.3) individuals compared to wild-rescued (M = 13.12, SD = 6.25, N = 19) and shy (M = 16.13, SD = 5.4, N = 16) lions. Sex and social-grouping of subjects did not show significant associations with behavioural welfare indices. Interestingly, behaviour diversity was reliably predicted by the enclosure usage patterns and aberrant repetitive behaviours displayed by subjects.

Discussion

Our findings underline the importance of individual-centric, behaviour-based, and multi-dimensional welfare assessment approaches in ex-situ conservation programmes. The results suggest that behavioural welfare indices complemented with individual variations can explain inter-individual differences in behavioural welfare measure outcomes of Asiatic lions. These findings also provide zoo managers with a non-invasive tool to reliably assess and improve husbandry practices for Asiatic lions. Understanding the unique welfare requirement of individuals in captivity will be crucial for the survival of the species.

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.

Relationships between captive chimpanzee (Pan troglodytes) welfare and voluntary participation in behavioural studies

Voluntary participation in behavioural studies offers several scientific, management, and welfare benefits to non-human primates (NHPs). Aside from the scientific benefit of increased understanding of NHP cognition, sociality, and behaviour derived from noninvasive behavioural studies, participation itself has the potential to provide functional simulations of natural behaviours, enrichment opportunities, and increased control over the captive environment, all of which enhance welfare. Despite a developing consensus that voluntary participation offers these welfare enhancements, little research has empirically investigated the ways that participation in behavioural studies may affect welfare. In the current study, we investigated potential relationships between captive chimpanzee welfare and long-term, repeated voluntary participation in noninvasive behavioural studies. We collected behavioural data on 118 chimpanzees at the National Center for Chimpanzee Care (NCCC) in Bastrop, Texas, USA between 2016 and 2018 using 15-minute focal animal samples. Additionally, we collected information on 41 behavioural studies conducted between 2010 and 2018 with the NCCC chimpanzees that involved exposure to a stimulus or manipulation. The total number of behavioural studies in which chimpanzees had participated over the approximately eight-year period was then examined in relation to levels of behavioural diversity, abnormal behaviour, rough scratching, inactivity, and locomotion using a series of regression analyses that controlled for rearing status and age of the chimpanzee at the time of data collection. Analyses revealed significant, positive relationships between the total number of studies in which chimpanzees participated and 1) behavioural diversity scores, R2 adj = .21, F(3,114) = 11.25, p < 0.001; and 2) rough scratching, R2 adj = .11, F(3,114) = 6.01, p = 0.001. The positive relationship between behavioural diversity scores and the total number of studies in which chimpanzees participated seems unsurprising, although we cannot draw conclusions about the directionality of this relationship. The result that rough scratching and the total number of studies in which chimpanzees participated were positively correlated is unexpected. However, rough scratching made up less than 1% of all activity in the current study, and as such, this result may not be biologically meaningful. These findings suggest that participation in behavioural studies is not likely to be detrimental to chimpanzee well-being, and may even be beneficial. Data such as these, which empirically investigate existing recommendations can help inform decisions pertaining to the participation of chimpanzees in behavioural research.

Refinements to captive chimpanzee (Pan troglodytes) care: a self-medication Paradigm

In an effort to enhance welfare, behavioural management continually refines methods of non-human primate (NHP) care. Chimpanzees (Pan troglodytes) are one of the most cognitively complex captive NHPs and they have been observed to self-medicate in the wild. The population of captive chimpanzees in the US is aged (due to a breeding moratorium instituted in 1998) and will progressively require more medical care as they get older. To functionally simulate natural self-medication behaviour, provide chimpanzees with the opportunity to voluntarily participate in their own healthcare, and open new avenues of communication between caregivers and chimpanzees, we used a medication choice paradigm that allowed chimpanzees to choose their daily arthritis medication. We provided four arthritic, mobility-impaired chimpanzees with meloxicam or ibuprofen in blue or green Gatorade® to establish associations between the coloured drinks and the effects of the medications. We subsequently gave each chimpanzee a choice between the two medications. Behaviour was recorded using 15-min focal animal observations. Mobility was assessed using interactive mobility tests and a caregiver-rating system. One chimpanzee showed a medication preference (ibuprofen over meloxicam). The chimpanzees exhibited no significant behavioural or mobility differences over time, suggesting that ibuprofen and meloxicam may not differ significantly in their ability to alleviate arthritic symptoms. Whether or not the chimpanzees show a medication preference, the opportunity to make meaningful choices and the functional simulation of a complex behaviour, self-medication, is present when using this medication choice technique. Furthermore, the paradigm itself could have potential applications for additional medication options and treatment regimens.