The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Sleep site selection of proboscis monkeys (Nasalis larvatus) in West Kalimantan, Indonesia


1Department of Anthropology, University of California-Davis, 2Graduate Group in Ecology, University of California-Davis, 3Graduate Group in Animal Behavior, University of California-Davis

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Proboscis monkeys (Nasalis larvatus) often sleep along rivers and form bands (aggregations of single male, multiple female units) at sleep site locations. While sleep site selection likely influences both the behavior and socioecology of this species, the factors underlying the choice of sleep sites are not fully understood. We examined how forest structure, weather, and insects influence sleep site selection by proboscis monkeys. We collected data on a wild population of proboscis monkeys living in three forest types in West Kalimantan, Indonesia for twelve months. We recorded the location of, characteristics of, and number of individuals in each tree, monitored changes in weather, and measured the abundance of insects and compared these data to random samples of trees and conditions throughout the forest. We found that proboscis monkeys preferentially chose to sleep in tall emergent trees located within ten meters of the river. The size of the tree positively correlated with the number of proboscis monkeys in sleep trees. Temperature and humidity seem to have little influence on the choice of the sleep tree sites. Proboscis monkeys tended to sleep slightly more inland when there was a high occurrence of sand flies on the rivers; mosquito densities varied in the different habitats, but did not seem to influence the location of sleep sites. These data indicate that grouping behavior of proboscis monkey are influenced by the availability of large sleep trees and that sleep site selection in our study groups is not solely shaped by anti-predator behavior.

This research was funded by Boren Fellowship, Fulbright Fellowship, and Primate Conservation, Inc.

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