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Animal profile
Nasalis larvatus
The proboscis monkey is a heavy-bodied, orange-brown leaf monkey endemic to Borneo, unmistakable for the pendulous nose of adult males and the pot-bellied profile of both sexes. It lives along rivers and swims well, crossing channels between roosting trees. Groups are usually one male with several females.
The drooping nose of an adult male is not only visual advertising. It acts as a resonating chamber that lowers and amplifies his calls, and nose size correlates with body mass and testis size, so the sound carries honest information about the caller.
Among the best swimmers of any primate, proboscis monkeys cross Bornean rivers by plunging in from overhanging branches. Their hind feet carry partial webbing between the toes, and they can travel underwater for stretches of tens of metres.