Group size: Determinants in the wild and implications for the captive housing of wild mammals in zoos

Group size is one of the most important factors influencing the formation and maintenance of successful social groups in captivity. For zoos, appropriate social groupings are of the utmost importance to provide examples of species-typical behaviors, as well as attain captive breeding goals. In the wild, group-living evolved largely in response to the need for predator avoidance and territory defense. The number of members in wild groups is a fundamental determinant of individual fitness, affecting net food intake and reproductive success. Captive animals encounter different environmental pressures than their wild counterparts; food availability and predation are no longer concerns, however they still face competition for mates and are unable to make the social adjustments necessary to decrease social tension. As such, group size has a large impact on the behavior, welfare and reproductive success of captive animals. Depending on the species, suboptimal sizes can be associated with increased abnormal behaviors and decreased reproductive success and infant survival in a range of captive mammals. However, in the absence of environmental constraints, many species can be housed in a greater diversity of social groups than observed in the wild. Thus, a key component of captive housing is flexibility.