Behavioral response of captive western lowland gorillas (Gorilla gorilla gorilla) to the death of silverbacks in multi-male groups

Survey of current group demographics and management practices of bachelor groups of western lowland gorillas (Gorilla gorilla gorilla) across North America

Recommendations for the successful management and maintenance of bachelor groups of western lowland gorillas (Gorilla gorilla gorilla) in zoological settings have been an increasingly prevalent focus within the zoological community. Over the past two decades, studies have examined the impact of various environmental factors on the stability of bachelor groups, proposed management strategies for bachelor groups, and compared behavioral trends between bachelor and mixed-sex groups. These studies have clearly demonstrated that bachelor groups are complex social units that require specialized management approaches. In this study, we aimed to assess the extent to which bachelor group management across North American zoos accredited by the Association of Zoos and Aquariums aligns with established recommendations. We distributed a comprehensive survey broadly encompassing habitat and housing, aggression and wounding, group demographics, feeding, and training to the 22 zoos housing bachelor groups as of 2019. We received completed surveys from 19 zoos, representing a total of 21 social units and 59 individual gorillas. We used descriptive statistics to represent the range of current management strategies across the surveyed population and ANOVAs to assess significant variation in key demographic variables. Our results demonstrate that a majority of zoos have adopted the best practices for the formation of social groups established by Stoinski et al. in 2004. However, there is much less standardization across zoos in protocols surrounding training and feeding. Additionally, important variables in the assessment of wounding, such as time of day and location, are often unknown or not observed by animal care professionals. We highlight these two areas as being of particular focus in developing and adhering to consistent protocols across institutions.

Why do some primate mothers carry their infant's corpse? A cross-species comparative study

Non-human primates respond to the death of a conspecific in diverse ways, some of which may present phylogenetic continuity with human thanatological responses. Of these responses, infant corpse carrying by mothers (ICC) is the most frequently reported. Despite its prevalence, quantitative analyses of this behaviour are scarce and inconclusive. We compiled a database of 409 published cases across 50 different primate species of mothers' responses to their infants' deaths and used Bayesian phylogenetic regressions with an information-theoretic approach to test hypotheses proposed to explain between- and within-species variation in ICC. We found that ICC was more likely when the infant's death was non-traumatic (e.g. illness) versus traumatic (e.g. infanticide), and when the mother was younger. These results support the death detection hypothesis, which proposes that ICC occurs when there are fewer contextual or sensory cues indicating death. Such an interpretation suggests that primates are able to attain an awareness of death. In addition, when carried, infant age affected ICC duration, with longer ICC observed for younger infants. This result suggests that ICC is a by-product of strong selection on maternal behaviour. The findings are discussed in the context of the evolution of emotion, and implications for evolutionary thanatology are proposed.

The utility of social network analysis for informing zoo management: Changing network dynamics of a group of captive hamadryas baboons (Papio hamadryas) following an introduction of two young males

Comprehensive knowledge of social groups within zoos allows for better understanding of the issues surrounding group stability and how to provide captive animals with optimal care. A developing area of sociality research that works to improve this understanding is social network analysis (SNA), which allows scientists to apply quantitative measures of group systems to represent social structure. In December 2015, Oakland Zoo introduced two new males to the hamadryas baboon (Papio hamadryas) exhibit. We examined the changing group structure of these baboons over the course of 6 months (July-December 2016) using social network analysis, specifically focusing on the changing social structure of the existing group and the utility of SNA methods for optimal care of captive animals. This study found that over time, the new males decreased their overall individual centrality, while some individuals had an increase in betweenness, a measure of an individual's intermediary role in the network. The results also illustrate the utility of social network analysis as tool for zoo management to examine how husbandry may have an impact on their animals, specifically for social species. Further research on the social networks of hamadryas baboon multi-clan formation could provide more information about the societal structure of this primate species, as well as the use of social network analysis as a valuable tool in captive animal management.

Personality and behavioral changes in Asian elephants (Elephas maximus) following the death of herd members

Elephants are highly social beings with complex individual personalities. We know that elephants have a general interest in death, investigating carcasses, not just limited to kin; however, research does not explore in depth whether individuals change their behavior or personality following traumatic events, such as the death of a conspecific. Within a captive herd of Asian elephants (Elephas maximus) housed at Chester Zoo, UK, we measured social behavior and proximity and personality using the Ten-Item Personality Inventory, and found age-related and relationship-related changes in both behavior and personality following the deaths of herd members. Overall, the herd spent less time socializing and engaging in affiliative behaviors following the death of the adult female when compared to baseline data, yet spent more time engaging in these behaviors after the death of two calves. The death of the central female had a dramatic impact on her infant calf, resulting in increasingly withdrawn behavior, yet had the opposite effect on her adult daughter, who subsequently established a more integrated role within the herd. Emotional Stability fell in the motherless calf but rose in an adult female, who had lost her adult daughter, but had a new calf to care for. We suggest that the greater impact on the behavior and personality of surviving herd members following the deaths of calves, compared to an adult member, attests to the significance of the unifying role played by calves within an elephant herd.

Death among primates: a critical review of non-human primate interactions towards their dead and dying

For the past two centuries, non-human primates have been reported to inspect, protect, retrieve, carry or drag the dead bodies of their conspecifics and, for nearly the same amount of time, sparse scientific attention has been paid to such behaviours. Given that there exists a considerable gap in the fossil and archaeological record concerning how early hominins might have interacted with their dead, extant primates may provide valuable insight into how and in which contexts thanatological behaviours would have occurred. First, we outline a comprehensive history of comparative thanatology in non-human primates, from the earliest accounts to the present, uncovering the interpretations of previous researchers and their contributions to the field of primate thanatology. Many of the typical behavioural patterns towards the dead seen in the past are consistent with those observed today. Second, we review recent evidence of thanatological responses and organise it into distinct terminologies: direct interactions (physical contact with the corpse) and secondary interactions (guarding the corpse, vigils and visitations). Third, we provide a critical evaluation regarding the form and function of the behavioural and emotional aspects of these responses towards infants and adults, also comparing them with non-conspecifics. We suggest that thanatological interactions: promote a faster re-categorisation from living to dead, decrease costly vigilant/caregiving behaviours, are crucial to the management of grieving responses, update position in the group's hierarchy, and accelerate the formation of new social bonds. Fourth, we propose an integrated model of Life-Death Awareness, whereupon neural circuitry dedicated towards detecting life, i.e. the agency system (animate agency, intentional agency, mentalistic agency) works with a corresponding system that interacts with it on a decision-making level (animate/inanimate distinction, living/dead discrimination, death awareness). Theoretically, both systems are governed by specific cognitive mechanisms (perceptual categories, associative concepts and high-order reasoning, respectively). Fifth, we present an evolutionary timeline from rudimentary thanatological responses likely occurring in earlier non-human primates during the Eocene to the more elaborate mortuary practices attributed to genus Homo throughout the Pleistocene. Finally, we discuss the importance of detailed reports on primate thanatology and propose several empirical avenues to shed further light on this topic. This review expands and builds upon previous attempts to evaluate the body of knowledge on this subject, providing an integrative perspective and bringing together different fields of research to detail the evolutionary, sensory/cognitive, developmental and historical/archaeological aspects of primate thanatology. Considering all these findings and given their cognitive abilities, we argue that non-human primates are capable of an implicit awareness of death.