LAUSR

Multiple ecological factors have been hypothesized to influence primate sleeping site selection. Testing multiple hypotheses about sleeping site selection permits examination of the relative strength of distinct ecological factors and expands our ability to understand how selection pressures influence primate sleeping behavior. Here we examine how avoidance of biting insects, thermoregulation, foraging efficiency, tree stability, and interspecific competition influence selection of sleeping sites by proboscis monkeys (Nasalis larvatus) in Indonesian Borneo. We collected data on relative insect abundance, temperature, rainfall, food availability, group size, sleeping site location, and presence of other primates for 12 mo. Using formal model comparison and information criteria, we analyzed the relative importance of these ecological factors in determining one aspect of sleeping site location: distance from the river. Our models supported the avoidance of biting insects and the foraging efficiency hypotheses. Proboscis monkeys slept further inland on nights when the abundance of sandflies was high along the river, and when less food was available along the river. Many studies suggest that primates select sleeping trees and locations to reduce predation risk; our study indicates that additional factors may also be important in determining sleeping site selection.