DOES INTRASPECIFIC VARIATION IN SOCIAL-SYSTEMS EXPLAIN REPORTED DIFFERENCES IN THE SOCIAL-STRUCTURE OF THE PROBOSCIS MONKEY (NASALIS-LARVATUS)

The social structure of proboscis monkeys (Nasalis larvatus) was inves tigated in the Brunei Bay area of Brunei Darussalam (Northern Borneo). Intraspecific variability in social systems had been suggested to occ ur in this species, with social structure varying with habitat differe nces. Prior reports for this area suggested that groups contained seve ral males, females, and offspring and were unstable. Contrary to these reports, I found that the monkeys were organized into groups containi ng one male, several. females, and offspring. These groups associated at sleeping sites at the river's edge, thus forming a secondary level of organization. This is the same social system reported in Sarawak, M alaysia and Kalimantan, Indonesia in different habitat types. It appea rs that methodological differences may account for the discrepancies b etween reports. I have found no evidence to suggest that intraspecific variation in social systems occurs in this species.