Proboscis Monkey

The nose

The male proboscis monkey’s nose is unique in the primate world. It grows throughout his life and can reach 10 cm or more, hanging down over the mouth. When the male makes his loud honking call, the nose straightens out and acts as a resonating chamber that amplifies the sound. Females prefer males with larger noses — they indicate age, dominance, and genetic quality. Female noses are much smaller and upturned.

Mangrove specialists

Proboscis monkeys are strongly associated with mangrove forests and riverine habitats. They are excellent swimmers — the best among primates — with partially webbed feet that help them cross rivers to escape predators or find food. They often leap spectacularly from tree branches into the water below. They live in harem groups of one adult male and several females with young.

Leaves and fermentation

Their diet is dominated by leaves, seeds, and unripe fruit. They have a complex, chambered stomach similar to ruminants that allows bacteria to ferment and detoxify the tannins and other compounds in leaves. This specialised digestion means they cannot eat ripe, sugary fruit — the rapid fermentation would cause dangerous bloating.

Endangered in Borneo

Deforestation for palm oil plantations and timber has destroyed more than half of Borneo’s lowland forest in recent decades. Proboscis monkey populations have declined by over 50% since 1970. They are entirely dependent on intact forest near water and cannot adapt to degraded habitat.