Social distancing: High population density increases cub rejection and decreases maternal care in the giant panda

Abstract

In conservation breeding centers, individuals are often housed in close proximity with an artificially high-population density. For many solitary species, these housing arrangements are in direct contrast to in-situ conditions. High-population density during pregnancy may lead to perceived competition for resources and danger to offspring, increasing stress and disturbance during gestation which has been shown to alter reproductive output, maternal care, and offspring behaviors. We conducted a retrospective analysis of reproductive outcomes for female giant pandas (Ailuropoda melanoleuca) and their infants housed in two different facilities with differing population density during gestation, birth, and postpartum. Our results indicate increased behaviors indicative of stress/anxiety in both mothers and cubs housed in high-density areas: mothers produced female-biased litters, rejected more cubs, and neglected their offspring more often, while infants increased squawking and vocalization rate. We suggest these findings may be explained by either higher levels of keeper activity causing external disturbances and/or the high-density of neighboring conspecifics as a form of social stress. Simultaneously, mothers in high-density areas also showed increased cub production and attentiveness toward their infants compared to mothers in low-density areas. The most plausible interpretation of maternal attentiveness findings is that higher levels of agitation in response to nearby conspecifics and/or keeper activity fostered higher levels of protective maternal behaviors. This, in turn, may have led to increased cub survivorship, or, alternatively, cubs at the high-density facility received more supportive care from keepers. We consider these findings preliminary due to the retrospective approach taken and the lack of replication across additional facilities with varying levels of social density. While experimental research is desirable to confirm these findings, we suggest that conservation breeding centers should prioritize research evaluating the effects of social density that are an inevitable but modifiable aspect of ex situ conservation.