Proboscis monkeys primarily eat the leaves, fruit, seeds and shoots of mangrove trees. They supplement their diet with some insect larvae. Their diets vary by season, and are based on fruit between January and May and leaves throughout the rest of the year.
Proboscis monkeys are found solely on the island of Borneo. They prefer mangrove forests near the coasts, generally near estuaries, rivers or swamps. They are adept swimmers, and even have some webbing between their fingers and toes. They are active during the day and live in social groups. These groups either consist of one male with several females or several males with no females. Each group contains between three and 32 individuals, and multiple groups often come together to sleep.
Proboscis monkeys are named for the large protruding noses on their faces, which are much larger on males than females. These large noses enhance the vocalizations of the males through resonance. The males are also much larger than the females. Females weigh between 15 and 26 pounds, while males weight between 35 and 48 pounds. The fur of proboscis monkeys is pink and brown, shading to red around the neck, and their hairless faces are a cream color..