Socioecological correlates of Chimpanzee (Pan troglodytes) hydration status at Gombe National Park, Tanzania

Maintaining water balance is imperative for organismal survival. Various socioecological conditions such as sex, reproductive state, and dominance rank can impact water intake and hydration status. Eastern Chimpanzees (Pan troglodytes schweinfurthii) present an interesting biological model to investigate the socioecological correlates of hydration status, given adult sex differences in behavior. Males are more gregarious than females, which may afford them less behavioral flexibility to reduce dehydration risk. However, females invest heavily in their offspring, producing a water heavy milk for up to 5 years, and adult females experience disparities in access to water in foods dependent on dominance rank, which may cause variation in hydration status. In the present study, we investigated correlates of adult chimpanzee hydration status at Gombe National Park, Tanzania, using a measure of urine concentration—urine specific gravity (USG)—highly concentrated urine results in a higher USG, indicating dehydration. We found that both males and females had significantly higher USG in the dry season, but males had lower USG than females during the dry season. Within females, reproductive state did not significantly impact hydration status; however, females in middle lactation tended to have higher USG than nonpregnant, nonlactating females. Additionally, high-ranking females had lower USG than mid- and low-ranking females. While our study showed consistency with USG values that have been demonstrated at other Chimpanzee research sites, we found evidence that this population may be chronically dehydrated by human standards, but more research is needed across populations to determine the health and fitness effects of chronic dehydration in Chimpanzees.