Twelve-year proximity relationships in a captive group of western lowland gorillas (Gorilla gorilla gorilla) at the San Diego Wild Animal Park, California, USA

Abstract

Proximity data were collected in a captive breeding group of gorillas (Gorilla gorilla gorilla) at the San Diego Wild Animal Park (currently called the San Diego Zoo Safari Park) twice a year (spring and fall periods) for over 12 years, by using a convenient method in which individuals less than 5 m from each animal in the group were recorded by scan sampling, approximately once per hour. Immature females from infancy to young adulthood maintained relatively frequent proximity to both their mothers and the silverback male and spent little time alone (no animals within 10 m), with relatively large individual differences. On the other hand, immature males decreased the time spent near their mothers and the silverback male and increased the time spent alone with increasing age. Therefore, sex differences in proximity to mothers and the silverback male became apparent after late juvenility. Some adult females maintained increased frequency of proximity to the silverback male than that by other females over the 12-year period, indicating the presence of long-term, stable proximity relationships between the silverback male and the adult females. Such long-term, stable proximity relationships were also observed among adult females. Some association patterns reported in wild gorillas, such as frequent proximity between adult females with dependent offspring and the silverback male and close relationships between related females, were not observed in the present study. The idiosyncratic or individual factors influencing some association patterns were easily reflected in captive situations.

Adult–adult play in captive lowland gorillas (Gorilla gorilla gorilla)

“…In this study, contrary to what is reported in the literature on wild and captive lowland gorillas (Fischer 1983;Stoinski et al 2003;Stokes 2004;Nakamichi et al 2014;Klailova and Lee 2014), adult females spent more time in spatial proximity to the silverback than to other females. In this view, the probability of social interaction (including play) between the silverback and adult females was enhanced.…”

Group structure and individual relationships of sanctuary-living Grauer’s gorillas (Gorilla beringei graueri)

“…The low association indices amongst individuals are similar to those reported between male-female mountain gorilla dyads within 2m in nature [ 4 ] suggesting the GRACE gorillas associate with one another similarly to mountain gorillas, their closest relatives. Association patterns of gorillas in zoos vary widely by study making comparisons to our findings challenging [ 49 , 70 – 72 ]. This may be reflective of the diversity of group-types, living spaces and management procedures within zoos, and possibly because the reporting of association patterns in zoos are often focused on a specific applied perspective, rather than a broad description of gorilla life in general.…”

“…As familiarity is the presumed underlying proximate mechanism driving kin biased behavior [ 74 ], it could be that the GRACE females who have lived together for many years since they were young have developed a familiarity with each other that is similar to what is observed in nature. Data from zoos, where females often live in groups for longer periods of time than they would in nature, similarly suggest that stronger association patterns amongst adult females occur compared to what is observed in nature [ 29 , 49 ]. Thus, these strong female-female relationships may be an artifact of living in human care.…”

“…However, this finding is from a single population of presumably closely related female gorillas and thus may be driven by group demographics not present in the GRACE group. Zoo studies are limited though monitoring of a single group over 12 years suggested female-female relationships were stable long-term [ 49 ]. However, this study did not describe these relationships in terms of strength and thus these relationships may have been stable but not necessarily strong.…”

“…Social relationships are significant contributors to the welfare status of primates [22,[38][39][40] and are sensitive to a variety of factors in human care. For example, primate social relationships can change in response to the introduction of new conspecifics [41][42][43], space availability [44,45], participation in cognitive research [46,47], the early life history of group members [48] and can also simply vary with time and developmental status of individuals [22,49,50]. Thus monitoring and quantifying social relationships within groups is an important procedure for ensuring optimal primate welfare [38,51].…”