It may seem hard to believe, but male proboscis monkeys use their fleshy, pendulous noses to attract mates. Scientists think these outsize organs create an echo chamber that amplifies the monkey’s call, impressing females and intimidating rival males.

Proboscis monkeys are endemic to the jungles of Borneo, never straying far from the island’s rivers, coastal mangroves, and swamps. They are a highly arboreal species and will venture onto land only occasionally to search for food. They live in organized harem groups consisting of a dominant male and two to seven females and their offspring. Various groups often congregate near water at night to sleep.

Proboscis monkeys are the primate world’s most prolific swimmers, frequently leaping from tree limbs and hitting the water