Aging-Related Behavioral Patterns in Tibetan Macaques

Aging can induce changes in social behaviors among humans and nonhuman primates (NHPs). Therefore, investigating the aging process in primate species can provide valuable evidence regarding age-related concerns in humans. However, the link between aging and behavioral patterns in nonhuman primates remains poorly comprehended. To address this gap, the present research examined aging-related behaviors exhibited by Tibetan macaques (Macaca thibetana) in their natural habitat in Huangshan, China, during the period from October 2020 to June 2021. We collected behavioral data from 25 adult macaques using different data collection methods, including focal animal sampling and ad libitum sampling methods. We found that among adult female macaques, the frequency of being attacked decreased with their age, and that the frequency of approaching other monkeys also decreased as age increased. In males, however, this was not the case. Our findings demonstrate that older female macaques exhibit active conflict avoidance, potentially attributed to a reduction in the frequency of approaching conspecifics and a decreased likelihood of engaging in conflict behaviors. This study provides some important data for investigating aging in NHPs and confirms that Macaca can exhibit a preference for social partners under aging-related contexts similar to humans.

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.

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.

An Evaluation of Ethograms Measuring Distinct Features of Enrichment Use by Captive Chimpanzees (Pan troglodytes)

Simple Summary

Environmental enrichment for chimpanzees is important in order to minimize boredom and stress in captivity and to provide opportunities to engage in species-typical behaviors. However, few studies have investigated potential associations between enrichment objects, manipulation behaviors, and social contexts, nor have they examined if individual chimpanzees vary in their enrichment object preferences. In the current study, three ethograms were used to code the use of enrichment objects, engagement in manipulation behaviors, and social contexts of enrichment use of captive chimpanzees (Pan troglodytes). Data mining from a video archive consisting of 2054 videos collected over a decade allowed the ethograms to be applied to 732 min and 58 s of videos. Some enrichment objects were more often associated with specific manipulation behaviors and social contexts, indicating that enrichment objects might serve distinct social and behavioral purposes. The chimpanzees differed in their enrichment object preferences, suggesting that caregivers of captive chimpanzees should consider individual needs when providing enrichment in order to improve chimpanzees’ experiences in captivity. Finally, the majority of enrichment object use and manipulation behaviors were able to be categorized, indicating that our ethograms were largely effective in coding enrichment use.

Abstract

Environmental enrichment provides mental stimulation and minimizes abnormal behaviors in captive animals. In captive chimpanzees, individual animals may vary in the ways in which they benefit from enrichment or use enrichment devices, so investigating nuances in enrichment use may improve the welfare of captive chimpanzees. In the current study, three ethograms measuring distinct features of enrichment use (i.e., enrichment object, manipulation behavior, and social context) were evaluated by coding videos of captive chimpanzees (Pan troglodytes) at Chimpanzee Sanctuary Northwest in Cle Elum, WA. A total of 732 min and 58 s of video footage was coded from a larger video archive (i.e., 2054 videos) of enrichment use that spanned a decade. A principal component analysis (PCA) revealed that different categories of enrichment objects were more often associated with specific manipulation behaviors and social contexts, suggesting that enrichment objects might fulfill different behavioral and social needs in captivity. Specifically, toy objects were associated with active tactile behaviors in affiliative contexts while oral behaviors were used with foraging objects in solitary contexts. Additionally, individual chimpanzees showed unique preferences for enrichment objects, indicating that caregivers of captive chimpanzees should consider individual needs instead of a “one size fits all” approach to enrichment provisions.

Social aging in male and female Barbary macaques

Aging brings about notable changes in sociality, with an increasing focus on essential partners in both humans and nonhuman primates. Several studies have shown that older nonhuman primates have fewer social partners and shift their types of interactions. The majority of these studies, however, involved only female individuals. Much less is known about the trajectory of social aging in males. We collected 2180 h of focal observation data in a large age-heterogeneous sample of 34 male and 50 female Barbary macaques (Macaca sylvanus; age range 5-30 years) living in two social groups at the outdoor enclosure at La Forêt des Singes in Rocamadour (France). To track age-related changes in social engagement of both sexes, we used classical behavioral and social network analysis to measure age-related variation in the number of partners, the frequency of affiliative interactions, and the position in the social network (eigenvector centrality and local clustering coefficient). We found that females were more central in most social network metrics than males, that is, had more social partners and were more engaged in affiliative interactions than males. We did not find notable sex differences with age: both sexes showed a similar decline in social activity and energy-demanding activities like jumping or running. Our results thereby extend our knowledge of older nonhuman primates' social life and emphasize that age can have a similar impact on female and male social behavior.

Shifting sociality during primate ageing

Humans exhibit major age-related shifts in social relationships along with changes in social and emotional psychological processes that underpin these behavioural shifts. Does social ageing in non-human primates follow similar patterns, and if so, what are the ultimate evolutionary consequences of these social shifts? Here we synthesize empirical evidence for shifts in social behaviour and underlying psychological processes across species. Focusing on three elements of social behaviour and cognition that are important for humans-propensities to engage with others, the positive versus negative valence of these interactions, and capabilities to influence others, we find evidence for wide variation in the trajectories of these characteristics across primates. Based on this, we identify potential modulators of the primate social ageing process, including social organization, sex and dominance status. Finally, we discuss how comparative research can contextualize human social ageing. This article is part of the theme issue 'Evolution of the primate ageing process'.

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.

Adolescent male chimpanzees (Pan troglodytes) form social bonds with their brothers and others during the transition to adulthood

Social relationships play an important role in animal behavior. Bonds with kin provide indirect fitness benefits, and those with nonkin may furnish direct benefits. Adult male chimpanzees (Pan troglodytes) exhibit social bonds with maternal brothers as well as unrelated adult males, facilitating cooperative behavior, but it is unclear when these bonds develop. Prior studies suggest that social bonds emerge during adolescence. Alternatively, bonds may develop during adulthood when male chimpanzees can gain fitness benefits through alliances used to compete for dominance status. To investigate these possibilities and to determine who formed bonds, we studied the social relationships of adolescent and young adult male chimpanzees (N = 18) at Ngogo in Kibale National Park, Uganda. Adolescent male chimpanzees displayed social bonds with other males, and they did so as often as did young adult males. Adolescent and young adult males frequently joined subgroups with old males. They spent time in proximity to and grooming with old males, although they also did so with their age peers. Controlling for age and age difference, males formed strong association and proximity relationships with their maternal brothers and grooming relationships with their fathers. Grooming bonds between chimpanzee fathers and their adolescent and young adult sons have not been documented before and are unexpected because female chimpanzees mate with multiple males. How fathers recognize their sons and vice versa remains unclear but may be due to familiarity created by relationships earlier in development.

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

The National Institutes of Health and the Association of Zoos and Aquariums recommend that captive chimpanzees be housed in multi-male, multi-female, age-diverse groups of no less than seven individuals. These recommendations are rooted in the idea that captive chimpanzee groups should be modeled after free-ranging, wild, fission-fusion chimpanzee societies. However, captive chimpanzees do not face the environmental pressures faced by wild chimpanzees, including food scarcity, inter-group competition, and predation. As such, it has been posited that wild, natural conditions may not be the most relevant metric for defining optimal captive chimpanzee group sizes and compositions. Additionally, captive housing poses a set of restrictions on group sizes and compositions, including the need to balance large, multi-male groups with space per animal limitations and intra-group aggression. In the present study, we examined the behavioral effects of group size, within-group age range, and percentage of males in the group. We collected 713 hr of focal animal samples across 120 captive chimpanzees housed in social groups of 4-10 individuals using a 58-behavior ethogram. Chimpanzees housed in groups with a large age range exhibited less inactivity and more locomotion than chimpanzees housed in groups with smaller age ranges. Additionally, chimpanzees in groups of ≥7 with less than half males showed the highest levels of locomotion. Lastly, chimpanzees in groups of ≥7 with at least half males showed the highest levels of affiliation. There were no other significant differences in behavior as a function of these variables or their interactions. These findings lend some support to the existing group size and composition recommendations, providing empirical evidence that there may be certain advantages to housing captive chimpanzees in larger groups with a more diverse age range and/or more males. These results also have practical implications for behavioral management programs across captive settings.

Social interactions and activity patterns of old Barbary macaques: Further insights into the foundations of social selectivity

Human aging is accompanied by a decrease in social activity and a narrowing in social networks. Studies in nonhuman primates may provide valuable comparative insights in which way aging impacts social life, in the absence of cultural conventions and an awareness of a limited lifetime. For female Barbary macaques at "La Forêt des Singes" in Rocamadour, France, we previously reported an age-associated decrease in active grooming time and network size. Here, we aimed to extend these findings by investigating in which way physical decline, spatial proximity, and aggression vary with age in female Barbary macaques. We analyzed >1,200 hr of focal observations for 46 females aged 5-29 years. As expected, older females engaged less frequently in challenging locomotor activity, such as climbing or running, than younger ones. The previously reported decrease in grooming time was not due to shorter grooming bout duration. Instead, active grooming bouts lasted even longer, which discounts the idea that manual fatigue explains the shift in grooming pattern. We found that older females tended to be spatially reclusive and that they were less frequently the targets of aggression. Although older females showed aggressive behaviors at similar rates as younger females, the proportion of low-level aggression (i.e., threats) increased with age. We suggest that these threats are not simply a signal of dominance, but also function to deter approaches by others. Overall, these findings are in line with the idea that older females aim to avoid potentially negative interactions, specifically if these are costly. In sum, these findings support the idea that shifts in female Barbary macaques' grooming activity, do not simply result from physical deterioration, but are instead due to a higher selectivity in the choice of social partners.

Comparative Pathology of Aging Great Apes: Bonobos, Chimpanzees, Gorillas, and Orangutans

The great apes (chimpanzees, bonobos, gorillas, and orangutans) are our closest relatives. Despite the many similarities, there are significant differences in aging among apes, including the human ape. Common to all are dental attrition, periodontitis, tooth loss, osteopenia, and arthritis, although gout is uniquely human and spondyloarthropathy is more prevalent in apes than humans. Humans are more prone to frailty, sarcopenia, osteoporosis, longevity past reproductive senescence, loss of brain volume, and Alzheimer dementia. Cerebral vascular disease occurs in both humans and apes. Cardiovascular disease mortality increases in aging humans and apes, but coronary atherosclerosis is the most significant type in humans. In captive apes, idiopathic myocardial fibrosis and cardiomyopathy predominate, with arteriosclerosis of intramural coronary arteries. Similar cardiac lesions are occasionally seen in wild apes. Vascular changes in heart and kidneys and aortic dissections in gorillas and bonobos suggest that hypertension may be involved in pathogenesis. Chronic kidney disease is common in elderly humans and some aging apes and is linked with cardiovascular disease in orangutans. Neoplasms common to aging humans and apes include uterine leiomyomas in chimpanzees, but other tumors of elderly humans, such as breast, prostate, lung, and colorectal cancers, are uncommon in apes. Among the apes, chimpanzees have been best studied in laboratory settings, and more comparative research is needed into the pathology of geriatric zoo-housed and wild apes. Increasing longevity of humans and apes makes understanding aging processes and diseases imperative for optimizing quality of life in all the ape species.

Assessment of reproductive behavior and hormonal cycles in geriatric western Lowland gorillas

The population of western lowland gorillas in North American zoos is aging and, as is the case with the aging human population, may have unique physical and social needs. We have documented previously that 25% of aging females (5/22) ceased to show reproductive cycles entirely, and could be defined as menopausal. Approximately 32% of females showed somewhat irregular cycling patterns. We review our hormonal and behavioral findings on reproductive aging in gorillas; describe the range of cycling patterns that we see and how we interpret these; and discuss the implications of these findings for captive management and husbandry of aging gorillas. We monitored fecal hormone metabolites (progestogens) in 30 gorillas and collected simultaneous behavioral data to evaluate the relationship between cyclicity and sexual behavior. We identified and described several discrete patterns of irregular cycling. These included extreme variability of cycle length, cyclic patterns with unusually low progestogen peak concentrations that possibly may not support luteal activity, and large variability in maximum progestogen peak height among cycles. All of these changes are consistent with age-related hormonal changes observed in humans and may be signs of changes in fertility as well. Behaviorally, nearly all cycling females exhibited signs of estrus. Affiliative behavior between male silverbacks and estrous females was observed in the control females, but not the geriatric females. These findings suggest that pre-menopausal females are exhibiting signs of perimenopause. As is the case in humans, such changes in hormone patterns may occur years before the onset of menopause. As enhancements in nutrition, husbandry, and veterinary medicine have led to increased longevity in our zoo populations of apes, it has become imperative that we investigate and better understand associated physiological and behavioral changes in geriatric animals to ensure appropriate management of this increasing demographic sub-population. Zoo Biol 0:1-23, 2007. (c) 2007 Wiley-Liss, Inc.

Effects of early rearing conditions on problem-solving skill in captive male chimpanzees (Pan troglodytes)

Early rearing conditions of captive chimpanzees characterize behavioral differences in tool use, response to novelty, and sexual and maternal competence later in life. Restricted rearing conditions during early life hinder the acquisition and execution of such behaviors, which characterize the daily life of animals. This study examined whether rearing conditions affect adult male chimpanzees' behavior skills used for solving a problem with acquired locomotion behavior. Subjects were 13 male residents of the Chimpanzee Sanctuary Uto: 5 wild-born and 8 captive-born. A pretest assessed bed building and tool use abilities to verify behavioral differences between wild- and captive-born subjects, as earlier reports have described. Second, a banana-access test was conducted to investigate the problem-solving ability of climbing a bamboo pillar for accessing a banana, which might be the most efficient food access strategy for this setting. The test was repeated in a social setting. Results show that wild-born subjects were better able than captive-born subjects to use the provided materials for bed building and tool use. Results of the banana-access test show that wild-born subjects more frequently used a bamboo pillar for obtaining a banana with an efficient strategy than captive-born subjects did. Of the eight captive-born subjects, six avoided the bamboo pillars to get a banana and instead used, sometimes in a roundabout way, an iron pillar or fence. Results consistently underscored the adaptive and sophisticated skills of wild-born male chimpanzees in problem-solving tasks. The rearing conditions affected both the behavior acquisition and the execution of behaviors that had already been acquired.

Quantitation of sleep and spinal curvature in an unusually longevous owl monkey (Aotus azarae)

BACKGROUND

A table summarizing the primary literature on 19 species of longevous non-human primates, other than owl monkey, is presented.

METHODS

We prospectively quantitated the sleep of a longevous female owl monkey (Aotus azarae), aged >30 years, longitudinally for 2 years and also evaluated the senility-induced change in spinal curvature.

RESULTS

The mean daily total sleep time (TST) of this monkey ranged between 790 and 1106 minutes, and was markedly higher in comparison with its female progeny (aged 16 years and used as a control) whose daily TST during the same experimental period ranged between 612 and 822 minutes.

CONCLUSIONS

The calculated kyphotic index (KI) of 2.27 for this monkey, compared with the KIs 4.83 and 5.42, for its progeny and female grandprogeny (aged 1 year) respectively, confirmed the prominent spinal curvature.

Controllability in environmental enrichment for captive chimpanzees (Pan troglodytes)

This study considers the use of nonsocial environmental enrichment by captive chimpanzees at the Primate Foundation of Arizona. The goal was to determine whether a relationship existed between controllability of enrichment items by captive chimpanzees and frequency of use. The study measured controllability, the ability of nonhuman animals to alter aspects of their environment by the potential destructibility of the enrichment item. This study examined additional factors that may affect enrichment use: individual age, sex, rearing history, social group composition, and availability of outdoor access. The chimpanzees in the study used destructible items--the enrichment category with the highest level of controllability--more than indestructible items across all age, sex, and rearing classes. Thus, controllability seems to be an important factor in chimpanzee enrichment. Younger individuals and groups with outdoor access used enrichment more than did older individuals and groups with indoor-only access. Individual sex, rearing history, and social group composition had minimal effects on enrichment use. These results support the importance of control to captive chimpanzees and further enable captive management to customize enrichment programs to the needs of particular animals.