Proboscis monkeys are endangered, riverine specialists from Borneo whose complex dietary and social needs make captive management exceptionally challenging. Few institutions hold them successfully, underlining the importance of habitat protection in the wild.
The highly specialised gut fermentation system of this species is disrupted by standard primate diets high in sugars and starches. Captive animals require access to specific leaf species and very limited fruit. Social structure — one-male harem units plus bachelor groups — must be replicated to prevent chronic stress and aggression. Riverine swim access and large arboreal enclosures with multi-level canopy are essential. The extreme difficulty of captive care makes in-situ conservation the primary welfare strategy.