Food Availability and Environmental Factors Are Associated With Seasonal Variation in Diet Composition and Activity Budgets of Stump-Tailed Macaques (Macaca arctoides) in Hollongapar Gibbon Sanctuary, Assam, India.

Seasonal variation in food availability and environmental factors can strongly influence the activity budgets and dietary composition of primates. However, year-long assessments remain limited for stump-tailed macaques (STMs). Using instantaneous scan sampling, we analyzed 4,836 scans collected over 405 observation hours across 115 days from a troop of 52 wild STMs between December 2022 and November 2023, spanning both dry and wet seasons. We used model-averaged beta and gamma regression models with harmonic seasonal terms to examine how food availability, environmental factors and seasonality influenced activity budgets, dietary composition and food species diversity of STMs. The activity budget comprised feeding (34%), resting (24.2%), moving (23.5%), grooming (13.9%) and other behaviors (4.5%). Moving was more frequent during the wet season (28.3%) and exhibited moderate seasonality, whereas resting was more frequent during the dry season (26.9%) and exhibited weaker seasonality. Across 32 food sources representing eight dietary categories, fruits constituted the largest proportion of the annual diet (34.8%), followed by roots (20.7%), tender bamboo shoots (16.1%) and leaves (15%). Fruits dominated the wet-season diet (61.7%), whereas roots and tender bamboo shoots constituted 67.8% of the dry-season diet. Fruit, seed and invertebrate consumption exhibited strong seasonality, while food species diversity increased with leaf availability. Despite seasonal variation in dietary composition, the proportion of feeding records remained relatively stable throughout the year. Overall, seasonality structured the activity budgets and dietary composition of STMs in response to changing resource conditions.