ON THE NOSE

Proboscis monkeys may be famed for their sizeable schnozzles but why do they have them? And what else is there to uncover about Borneo’s peaceful primates?

- Jo Price

Endemic to the jungles of Borneo, proboscis monkeys never stray far from the tropical island’s rivers, coastal mangroves and swamps. Dawn and dusk are the best times to watch these arboreal primates. In the evening, they often congregate by the water to sleep. So, along with my fellow travellers, that’s when I head out onto the river.

Our small boat speeds along the murky, tree-lined Kinabatangan as a pair of oriental pied hornbills fly overhead. Everyone keeps a close eye on the riverine foliage for any sign of movement and their first glimpse of proboscis monkeys. It doesn’t take long before a group is spotted settling in the trees for the night. We cut the engine and drift quietly towards the riverbank.

The selection of sleeping sites by proboscis monkeys along this river in the Malaysian state of Sabah is mostly influenced by antipredation strategies, and is crucial for the primates’ survival, according to a Folia Primatologica study.

Within identified sleeping sites, trees were taller, had a larger trunk, and bigger and higher first branches than surrounding trees. Scientists also observed that females and youngsters stayed higher in the canopy than males, perhaps due to their vulnerability.

There are two types of social groups in the proboscis monkey: harem groups (which consist of a dominant male, an average of five females and their offspring) and all-male bachelor groups. We’re watching a harem group, and the dominant male is watching us.

Resident or core males in harem groups have a tenure of about six to eight years: “If he loses interest, the females will kick him out,” says wildlife guide Ronald K Asuncion.