Proboscis monkeys are Borneo's most threatened primate, with their riverine forest habitat decimated by oil palm expansion, logging, and coastal development.
Proboscis monkeys in degraded habitat experience chronic welfare stress. Loss of sleeping trees forces groups to roost on exposed branches or in plantations, increasing predation risk and stress. Fragmented populations must cross open ground or swim rivers — both high-risk activities. Animals caught in forest fragments face food shortages, especially of the specific leaves, seeds, and fruit they require; malnutrition is documented in isolated groups. Wildlife conflict with plantation workers results in killings. Infants and juveniles are most vulnerable during forest-clearing events. The species' specialized digestive system (which processes toxic secondary plant compounds) means they cannot substitute alternative foods when native forest is lost.