Microclimatic effects on activity patterns in a montane chimpanzee population.

Climatic variation can shape primate activity budgets by altering the energetic and thermoregulatory costs of feeding, resting, locomotion and social behaviour. However, little is known about how chimpanzees that inhabit cool, wet montane forests adjust their activity in response to fine-scale meteorological conditions. We examined the effects of temperature, absolute humidity (water vapour pressure (WVP)), wind speed and rainfall on eastern chimpanzees (Pan troglodytes schweinfurthii) in Nyungwe National Park, Rwanda, one of the highest-elevation chimpanzee habitats. From March 2024 to February 2025, we collected 1933 party scans and 5661 individual scans, together with scan-level microclimatic measurements. Rainfall showed the clearest behavioural association: feeding probability declined during rainfall, whereas resting increased. Wind speed was negatively associated with both locomotion and grooming, suggesting that windier conditions may constrain movement and social behaviour. Temperature, WVP and fruit availability showed no clear association with any of the four behaviours. Feeding probability was higher and resting probability lower in the wet season than in the dry season. Harmonic beta-binomial generalized linear mixed-effects models revealed pronounced daily rhythmicity in feeding and resting. Overall, Nyungwe chimpanzees maintained broadly conserved daily activity rhythms while selectively adjusting behavioural allocation in response to immediate meteorological conditions.