Autism spectrum disorder (ASD) is a developmental disorder characterized by stereotypies or repetitive behaviors and impairments in social behavior and socio-communicative skills. One hallmark phenotype of ASD is poor joint attention skills compared to neurotypical controls. In addition, individuals with ASD have lower scores on several of the Big 5 personality dimensions, including Extraversion. Here, we examine these traits in a nonhuman primate model (chimpanzees; Pan troglodytes) to further understand the relationship between personality and joint attention skills, as well as the genetic and neural systems that contribute to these phenotypes. We used archival data including receptive joint attention (RJA) performance, personality based on caretaker ratings, and magnetic resonance images from 189 chimpanzees. We found that, like humans, chimpanzees who performed worse on the RJA task had lower Extraversion scores. We also found that joint attention skills and several personality dimensions, including Extraversion, were significantly heritable. There was also a borderline significant genetic correlation between RJA and Extraversion. A conjunction analysis examining gray matter volume showed that there were five main brain regions associated with both higher levels of Extraversion and social cognition. These regions included the right posterior middle and superior temporal gyrus, bilateral inferior frontal gyrus, left inferior frontal sulcus, and left superior frontal sulcus, all regions within the social brain network. Altogether, these findings provide further evidence that chimpanzees serve as an excellent model for understanding the mechanisms underlying social impairment related to ASD. Future research should further examine the relationship between social cognition, personality, genetics, and neuroanatomy and function in nonhuman primate models.

For management and/or research purposes, chimpanzee mothers and their offspring are often physically separated from one another at an earlier age than they would be in the wild. Studies of the behavioural and physiological effects of mother-infant separation on infant behaviour have been conducted in both human and nonhuman primates. However, few studies have been conducted to examine the response of the mother to separation from her infant, particularly in great apes. The current study opportunistically examined the response of twelve chimpanzee mothers to separation from 15 of their offspring ranging from 1.8 to 5.4 years of age. Behavioural data (proximity of the mother to other group members, and fifteen behaviours representing six categories [agonistic, prosocial, vocalisations, abnormal, locomotor, inactive]) were collected for three weeks prior to and three to five weeks following the permanent removal of the offspring from their mothers. A repeated measures MANOVA conducted on all subjects revealed no significant change in behaviour following separation. There was a significant increase in inactivity following separation of the offspring (F2.21 = 5.47, P < 0.05) in a subgroup of mothers (n = 8) that was studied more intensively on the first day of separation. Maternal age, infant age, presence of other offspring, and past experience with mother-offspring separation had no effect on response to separation. These results contradict those of mother-infant separation studies in monkeys and indicate that most behavioural indicators of well-being are stable in chimpanzee mothers that remain in their familiar environment and social group following offspring separation.

This study measured the amount of time 17 chimpanzee infants devoted to stereotyped body rocking in a variety of nursery settings. Nine females and eight males ranging in age from three weeks to four years were included in the study. Some infants were placed in a peer group at a very early age and were given minimal human contact, while others were provided with more frequent human interaction and were placed in peer groups at varying ages. During the course of the study, infants were housed with varying numbers of chimpanzee companions and some were also provided with a canine companion. Four hundred and thirty-three hours of data were collected. Infants showed a decline in rocking over age and rocked less in the presence of a canine companion. Infant gender, the amount of human contact received at an early age, the age placed with at least one peer companion, and the current number of chimpanzee companions did not affect the time devoted to body rocking. These findings demonstrate that animal managers should look beyond conspecific stimulation for improving the social environment and overall welfare of chimpanzees. These results are further discussed in a framework of identifying possible strategies for minimizing rocking and promoting future behavioural competence in nursery-reared infants.

Chimpanzees (Pan troglodytes) that are kept in captivity come from a wide variety of backgrounds, and a proportion of them have been subjected to maternal separation and social deprivation during development. The long-term effects of such practices have received little investigation. This study investigates whether the removal of infants from their mothers and/or other chimpanzees affects their activity levels and abnormal behaviours later in life. A total of 69 resocialised chimpanzees were studied at six zoos in the United Kingdom. Chimpanzees were categorised into one of three rearing conditions: reared by their mother in a group of conspecifics (MGR); reared with other conspecifics but separated from their mothers (RO); and reared apart from their mother or other conspecifics for a period of time during infancy (RA). Results indicate that ‘socially deprived’ individuals show reduced levels of normal activity, elevated levels of abnormal behaviours and a wider repertoire of abnormal behaviours. These differences were more pronounced in younger individuals, with adults from the three different rearing conditions performing abnormal behaviour patterns at comparable levels. It is concluded that human-rearing, either alone or with conspecifics, influences behaviour through suppression of normal activity levels as a result of separation and elevation of levels of abnormal behaviours as a mechanism for coping with maternal loss and restricted rearing. However, these effects are not irreversible and recovery of ‘normal’ behaviours may occur with access to an enriched social environment.

The effects of maternal and peer separation during infancy and juvenescence on adolescent and adult chimpanzee behaviour were studied. The aim was to provide an insight into the social development of the species and to investigate human influence on this process. Forty-three adolescent and adult chimpanzees (Pan troglodytes), from a variety of backgrounds, were studied at five zoos in the UK. Details of play and grooming interactions were recorded. Competence at initiating, maintaining and contributing to play and grooming interactions was assessed. It was predicted that, regardless of their present environment, captive chimpanzees that were reared without their mother would be less competent and complex in these social abilities than mother-reared chimpanzees. Results indicated that the chimpanzees' social skills showed few detrimental effects of maternal separation. Nevertheless, individuals that had been human-reared demonstrated more unsuccessful initiations of social interactions and fewer polyadic grooming interactions than their mother-reared peers. Therefore, rearing background may have only a limited effect on adult chimpanzees' social competence. Adult chimpanzees that were hand-reared or nursery-reared may be exhibiting a recovery of their social skills, or they may be unaffected by their rearing background; alternatively, the effects of rearing may have been masked by more significant factors, such as current management.

Human interaction as environmental enrichment for chimpanzees (Pan troglodytes) and other primates is widely promoted and believed to be of value, but has been subject to little objective evaluation. This study assessed the effects of positive human interaction (eg relaxed treat feeding, playing, and other forms of social interaction compatible with personnel safety) on the behaviour of adult chimpanzees. Subjects were housed indoors in groups of two or three individuals. The level of interaction during routine care and management (ie in the process of cleaning, feeding, and monitoring) represented the baseline condition. The test condition involved a familiar caretaker spending an additional 10 mins per day, 5 days a week, with each chimpanzee. This study was designed to assess carry-over effects of interaction on behaviour outside the context of care staff presence. Therefore, in all phases of the study, data (97 h of focal animal sampling) were collected only when caretakers were absent from the building. During the increased human interaction phase, the chimpanzees groomed each other more and showed lower levels of the following behaviours: regurgitation/reingestion, other oral abnormal behaviours, inactivity, and reactivity to the displays of neighbouring groups. A trend towards reduced agonistic display was also detected. Attempted interactions with the observer shifted significantly from predominantly aggressive to predominantly affiliative in nature. These results suggest that simple, unstructured affiliation between humans and chimpanzees should be a valued component of behavioural management.

The use of woodchips as bedding for 16 juvenile chimpanzees (Pan troglodytes) was evaluated for the effects on behaviour, health and husbandry practices. Woodchip bedding was placed in two outdoor play areas for five consecutive days. Behavioural data were recorded in the morning and afternoon of each day, and compared to pre- and post-test data. A total of 44 hours of observations, made up of 1 hour scan sample sessions, were completed for the study. Behaviours in the following categories were measured: abnormal, affinitive, aggressive, environmental manipulation, inactivity, locomotion, play, self manipulation and woodchip manipulation. The location of each animal was also recorded Analysis of the data indicated that the chimpanzees engaged in woodchip-related behaviours for an average of 20.52 per cent of the data points, and that they spent more time manipulating the substrate in the morning than in the afternoon. In addition, abnormal behaviour, environmental manipulation and affinitive behaviours were significantly lower during the woodchip condition than during pre-test and post-test conditions. The subjects spent the most time on the floor of the enclosure, and this measure did not differ between conditions. The woodchip bedding did not cause any known health problems for the chimpanzees. Although the daily addition and removal of woodchips took more time than did routine cleaning, it kept the play areas cleaner and drier. The evaluation of woodchip bedding as enrichment was favourable and indicated that bedding may be used regularly in the maintenance of captive chimpanzees.

The behavioural development of 90 chimpanzees (Pan troglodytes) was followed. Of these, 65 had been separated from their mothers to prevent casualties or, at a later age, to increase breeding success. Some showed body rocking and others did not. To obtain insight into the causes of the onset and development of body rocking, chimpanzees raised with peers, with their mother, or in a semi-natural group were compared Rocking was never observed in the semi-natural group. It was occasionally seen when with the mother. Separation from the mother soon after birth induced anxiety and rocking developed after sitting upright had developed. Rocking levels of three per cent of the time were still present at seven to nine years of age.

The most probable causes of the development of rocking are frustrating social circumstances and the inability to cope with these. Merging groups, disturbances and the introduction of a fearful object increased rocking in the individuals that had developed the habit. However, rockers reacted less to those circumstances than non-rockers, showing smaller increase in body contact and less reduction of play. This finding suggests that rocking, instead of being a bizarre reaction to unsurmountable stress, could be a behaviour that helps an individual to cope with difficulties and stress. In terms of animal welfare, rocking in chimpanzees housed in laboratory conditions is an indication of a less optimal reaction pattern to frustrating circumstances. The development of rocking may be prevented if the babies are left with the mother and in their social group. Rocking after (late) separation may be prevented when transfer takes place together with familiar peers.

In the wild, chimpanzees spend most of their time foraging, so any device that stimulates this behaviour in captivity could potentially be effective enrichment. A simple grass foraging device constructed of a polyvinyl chloride (PVC) pipe cut in half lengthwise and planted with rye grass seed was designed to allow captive chimpanzees living in non-grassy enclosures to exhibit foraging similar to that of their wild counterparts. The grass containers were attached to the outside of six different enclosures. Observational data were collected on 14 adult chimpanzees (eight females, six males) within groups of either two or four members. A total of 54 hours of behavioural observations were conducted and comparisons were made across three conditions: baseline; grass container; grass container with extra foraging material (one half cup of sunflower seeds). Subjects used the grass container for 4.0 per cent of their time, but for 19.8 per cent of their time when the grass container with extra foraging material There was no statistical evidence of habituation to the device. Overall, the grass container only increased time spent foraging when it contained additional food items. Since behavioral benefits associated with this device are few, its potential application is limited.

Captive chimpanzees fed at regular, predictable intervals are known to exhibit higher rates of aggression immediately prior to, and during feeding. Presumably, anticipation of food creates tensions leading to increased agonistic interactions prior to feeding. This study was conducted to determine if seasonal variabilities might contribute to pre-feeding agonism. A quantitative examination was made looking at events affected by seasonal (summer versus autumn) changes. Seasonal fruit diversity and the amount of available space during feeding bouts in socially housed, captive chimpanzees were tested for an effect on pre-feeding agonism. Groups were observed for a five-week period during both seasons. Each social group was observed five times per season for 30 minutes, beginning 30 minutes prior to the morning feeding. All occurrences of agonistic behaviours were recorded. Average frequencies of agonistic behaviours were calculated for each group and compared across season using a Wilcoxon matched-pairs test to determine the effect of seasonal fluctuations in fruit diversity. There were no significant differences in the number of agonistic behaviours exhibited during summer versus autumn seasons. A strong negative correlation was found for agonistic behaviours in both seasons: as space decreased, agonism increased in both summer and autumn. In addition, males scored significantly higher in the summer versus the autumn for submissive behaviours when space decreased. The provision of a variety of seasonal fruits did not result in increased pre-feeding agonism in captive chimpanzees. In fact, cage size had a greater effect on levels of agonism than did the provision of seasonal fruits.

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.

Abnormal behaviour in captive animals is both pervasive and ambiguous. Although individual differences are central to the field of animal welfare, studies on abnormal behaviour predominantly employ quantitative, population-level approaches. For example, whereas previous studies on chimpanzee (Pan troglodytes) abnormal behaviour have reported significant variation between groups or individuals in the quantity (eg frequency and duration) of abnormal behaviour, much less is known about qualitative differences. Individual abnormal behavioural repertoires may be highly idiosyncratic, where certain behaviours are over-represented (ie individually specific abnormal behavioural ‘signatures’). The present study investigated qualitative individual variation in the abnormal behaviour of chimpanzees (n = 15) housed at Royal Burgers’ Zoo in Arnhem, The Netherlands. Substantial variation was found between individuals in the diversity (size and evenness) and overall composition of their abnormal behavioural repertoires. Factors including age, sex, and rank did not significantly account for dissimilarity of individuals’ abnormal behavioural repertoires, but kin dyads showed more similar abnormal behaviour than non-kin dyads. Further exploratory analyses examined whether individual variation in one abnormal behaviour (coprophagy) predicted variation in stress-related behaviour (self-scratching). This allowed us to tentatively conclude that there were also individual differences in the link between a given abnormal behaviour and the behavioural expression of stress. Qualitative individual variation in abnormal behaviour provides a novel angle to a literature traditionally focused on quantifying abnormal behaviour at the group- or species-level and may thus represent an important yet previously overlooked source of variation in the extent to which abnormal behaviour reflects the state of individual welfare.