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.


Night monkeys are found in Argentina, Bolivia, Brazil, Colombia, Nicaragua, Panama, Paraguay, and Venezuela.


Night monkeys inhabit evergreen tropical rainforests and deciduous scrub forests. They also occupy forests along rivers. They prefer dense middle-level canopies and understories with tangled vines that provide cover for sleeping sites. They also like hollows in old trees.


Night monkeys eat mainly fruits, but also consume leaves, flowers, insects, tree frogs, spiders, bats, birds, and eggs. They forage, search for food, at all levels of the forest, from the canopy down to the forest floor.


Night monkeys are arboreal and live in family groups consisting of an adult pair and two or three offspring. During the day, the family sleeps in tree hollows or tangled vines. At night they forage for food throughout the forest levels, sometimes descending to the ground. They are especially active on moonlit nights, when they can see better. Night monkeys are adaptable. In Argentina, when the nights get cold at certain times of the year, the animals sleep at night and look for food during the day.

Night monkeys are monogamous (muh-NAH-guh-mus), having just one partner. The female gives birth to one offspring a year. The mother nurses the infant for up to eight months, but only carries the infant during the first week after birth and when nursing. The father provides almost all the child care. He carries the infant when the family travels through the trees. He also plays with the infant and the older offspring and guards them from predators, animals that hunt them for food. If the father dies, the older sibling, not the mother, assumes infant care. The young leave home at about three years of age.

Night monkeys scent mark territories with a behavior called urine washing. They wet their hands with urine, then rub them on their coats and the soles of their feet. The urine scent is transferred to the leaves and branches during their travels. They also communicate using secretions from scent glands on the chest and on the base of the tail. Conflicts between neighbors tend to occur when the moon is bright, perhaps because they can better see aggressive physical signals that include arching the back, erecting the fur, passing wastes, and urinating. The monkeys emit a variety of calls, including shrill cries, squeaks, and loud owl-like hoots that can be made louder by inflating the throat sac. Young males wishing to attract a mate hoot for long periods of time during a full moon.


Night monkeys are hunted for their meat and fur by native people. They are sold as pets and used for medical research.


The IUCN lists the Andean night monkey as Vulnerable, facing a high risk of extinction in the wild, because of small populations and habitat destruction from deforestation. The gray-bellied night monkey is also classified as Vulnerable due to hunting by humans and collection for the pet trade and medical research.