Investigation of Warm Water Enrichment on Drinking Behavior in Older Rhesus Macaques

Older animals in a managed setting (e.g., zoos) may require special care. Previous studies have suggested reduced water intake in rhesus macaques may result from cold environment and aging, leading to a decline in their welfare. This study aimed to assess whether providing warm drinking water influences water consumption and preference in aged rhesus macaques. The experiment was conducted on 11 older rhesus macaques at the Kyoto City Zoo, Japan. Observations were conducted for 42 days between November 21, 2024 and April 12, 2025. Containers filled with room-temperature water or warm water were placed in an indoor habitat, and the drinking behavior of the rhesus macaques was recorded for 20 min. No significant difference was found in the drinking frequency between the two water temperatures. However, the time spent drinking in each bout was significantly longer when warm water was provided than when room-temperature water was provided. Furthermore, when room-temperature and warm water were placed simultaneously, the drinking behavior of rhesus macaques was significantly biased toward the warm water container. In other words, rhesus macaques showed a preference for drinking heated water, suggesting that installing warm water may improve the drinking environment for older rhesus macaques.