The chimpanzee that never drank: re-evaluating the ecological impact of water on the behaviour of wild rainforest-living chimpanzees

Climate change is predicted to negatively impact global water availability. For effective conservation, research on the ecological role of water is essential - to date, especially little is known about it in mesic environments. In this thesis, I explore the ecological impact of water availability on the behaviour of a community of wild eastern chimpanzees (Pan troglodytes schweinfurthii), a species often assumed to be independent of surface water outside of arid environments, living in an equatorial rainforest in Uganda. Using long-term observational, phenology, and climate data, fieldwork observational data, and camera trap videos, I re-evaluate previous findings on the presence of drinking and water-contact behaviour in rainforest chimpanzees and add new knowledge on how water acts on chimpanzee space use and social behaviour. The chimpanzees studied drank water daily and showed no hydrophobia. While they drank more often in the dry season, daily drinking behaviour was present regardless of season. All regularly observed chimpanzees above the age of 2.5 years were seen drinking. Low water availability corresponded with constrained female space use around a fallback water source, with individual home ranges significantly smaller during the dry season. Core area structure also changed with water availability: interindividual overlap increased during the dry season, and core area centres shifted between the wet and dry season. Additionally, all 50% core areas included a fallback water source during the dry season compared to chance level during the wet season, the use of which increased as water scarcity intensified. Female social behaviour and networks were also characterised by high seasonal variability corresponding to water availability. Females were more gregarious in the dry season, but had more constrained proximity and grooming networks, characterised by a reduction in the number of partners, while maintaining even bond strength. The findings provide an example of water being a major shaper of behaviour in a mesic environment and have broader implications for behavioural ecology, conservation, and human evolution.