Mantled howler monkeys (Alouatta palliata) modify activity and spatial cohesion in response to seasonality

Longer, more severe dry seasons are impacting wildlife populations that depend on stable seasonality. Howler monkeys in tropical rainforests rely on consistent seasonal durations for food. We investigated mantled howler monkeys' (Alouatta palliata) response to seasonality at La Selva Research Station, Costa Rica, by comparing their activity and spatial cohesion patterns across seasons. We predicted monkeys would rest less, feed and travel more, and be less spatially cohesive during the dry season than the wet season due to decreased resources. We collected 553 hours of data on monkey activity and spatial cohesion using instantaneous focal sampling across wet and dry seasons from 2018-2023. Monkeys spent significantly less time resting and more time feeding, with a higher median distance between nearest neighbors in the dry season compared to the wet season (resting: 69.0% vs. 75.3%; feeding: 14.7% vs. 7.9%; neighbor distance: 2.1m vs. 1.5m). These results suggest lower nutritional yields in the dry season require increased feeding while decreased feeding competition during the wet seasons enables higher spatial cohesion. Since many primates rely on stable seasonality, primates across the tropics will likely need to modify their behavior as climate change continues to increase the length and severity of dry seasons. It is therefore crucial to examine how howler monkeys and other primates respond to seasonal changes over many years to understand the impacts of climate change more fully, and to determine the limits of behavioral flexibility in the face of climate change.