Patterns of Sleeping Site and Sleeping Tree Selection by Black-and-Gold Howler Monkeys ( Alouatta caraya ) in Northern Argentina

The selection of sleeping sites and sleeping trees in nonhuman primates is related to social and ecological factors. We investigate the role of body stability, risk of parasite infection, access to food, and range defense in the sleeping behavior of black-and-gold howler monkeys ( Alouatta caraya ) in northern Argentina. We collected data for 4 groups over 12 mo (198 study days). Black-and-gold howlers used 12 of 36 available tree species as sleeping trees. In comparison to the available trees, sleeping trees had a larger diameter at breast height, greater total height, and greater height of the lowest branch. Monkeys used large branches to sleep more frequently than small branches. Our results suggest that howlers avoided using the same sleeping tree on consecutive nights. At sleeping trees, individuals descended to lower branches to defecate. Sleeping sites were close to morning feeding sites. More sleeping sites were located in areas of range overlap between groups (75%) than in exclusive-use areas (25%), and sleeping sites located in overlapping areas were used more frequently when neighboring groups were nearby than when they were far away. Our results suggest that body stability, parasite avoidance, access to food, and range defense all affect the selection of sleeping sites.