Night Monkeys: Aotidae

Night monkeys, so named because they are the world's only nocturnal (active at night) monkeys, are medium-sized animals weighing about 2 pounds (0.9 kilograms). They measure about 13.5 inches (34 centimeters), with a tail length of about 14.6 inches (37 centimeters). Forward-facing, large eyes dominate the round face. The large size of the eyes makes up for the lack of a reflective eye layer used by many nocturnal mammals for night vision. Night monkeys are also called owl monkeys because of their round, flat face and eyes that resemble those of an owl.

Night monkeys have a thick, woolly fur that ranges in color from gray to brown, with yellow to orange undersides. An orange stripe runs down the back. Large white or gray patches surround the eyes and the mouth. Three dark stripes extend from the top of the nose and on each side of the head. The stripes vary in darkness and width. Very small rounded ears seem almost absent in the thick fur. A sac under the chin can be inflated to make vocalizations louder. The long, bushy tail is non-prehensile, or incapable of grasping. It is used for balance when traveling through the forest on hands and feet and for leaping.