The Maroon Leaf Monkey is found on the southeast Asian island of Borneo and the nearby smaller Karimata. They mostly live in forests at altitudes below 2,000 m. They feed on leaves, seeds and fruits and are equipped with a large, chambered stomach like a cow, which allows them to digest their fibrous food. They avoid sweet, ripe fruit because the sugars disrupt the delicate balance of their complex stomachs. They live in bands of 2 to 13 individuals, led by a dominant male, and spend nearly all their time in the trees. They have broad, dark-colored faces with wide, expressive eyes and average between 6.2 to 6.3 kilograms. They are highly territorial and will challenge any intruders within their home range. Males emit a loud call to demarcate their territory and warn rivals. This species is under some pressure from hunting and habitat loss, but they are still quite common throughout their range. They are protected by law throughout Malaysian Borneo.