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.