Mothers Frequent Caves: Lactation Affects Chimpanzee (Pan troglodytes verus) Cave Use in Southeastern Senegal

Caves play an important ecological role for nonhuman primates in Africa and Asia. Savanna chimpanzees (Pan troglodytes verus) living in the Mandingue plateau of Senegal and Mali use caves for thermoregulation, where these refugia provide a cool microclimate during the hot, dry season. In this study, we examined cave use frequency for a chimpanzee community in southeastern Senegal. We used images from a camera trap placed at the mouth of a large laterite cave to investigate the hypotheses that sex, reproductive state, and seasonality influence the frequency of cave use. The camera collected 14,053 still images of chimpanzees between 2011 and 2013 over 325 camera trap days. Our results indicate no difference in cave use frequency between males and females overall. However, female reproductive state did significantly influence cave use, with lactating mothers using the cave more frequently than both males and nonlactating females. Chimpanzees used the cave during the hottest times of the day and were more likely to visit the cave during periods of low water availability and high maximum temperatures associated with the dry season. These results suggest the importance of thermoregulation in extreme heat for all individuals, and specifically for lactating females with nursing infants that likely experience higher metabolic and hydration stress. This study provides insight into the dynamics of primate cave use by contributing evidence that chimpanzee cave use may be influenced by reproductive states in addition to thermoregulatory needs.