Notes on the size and composition of groups of proboscis monkey, Nasalis larvatus

Proboscis monkeys, Nasalis larvatus, were observed from a boat in coastal mangrove swamps in Brunei. The size of foraging parties varied from 2 to 63 individuals and there was evidence that these parties were of ephemoral composition. Mean group size was 13.8 (mode 6-10). Overall, parties comprised males:females:juveniles in the ratio 1:2.6:1.8. It is suggested that variation in the size of foraging parties may be a consequence of the patchy distribution of food trees amongst a forest of inedible Nipa fructicans.