NIGHT MONKEYS: Aotidae

PHYSICAL CHARACTERISTICS

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.

GEOGRAPHIC RANGE

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

HABITAT

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.

DIET

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.

BEHAVIOR AND REPRODUCTION

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 AND PEOPLE

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

CONSERVATION STATUS

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.

THREE-STRIPED NIGHT MONKEY (Aotus trivirgatus):SPECIES ACCOUNT

Physical characteristics: The three-striped night monkey has a woolly, dense fur that varies in coloration from grizzled gray to brown to reddish. Its undersides are orange or yellowish. The ears are small and rounded. Very large eyes are forward-facing and are brown or orange. Large white patches surround the eyes and the mouth, giving the appearance of alertness even when sleeping. Three dark stripes extend from the top of the nose and on each side of the head. The distinctive facial markings may prove helpful for communications among family members, especially on moonless nights. The legs, which are longer than the arms, are used for jumping. An inflatable

sac under the chin is used to produce loud vocalizations. The orange, bushy tail, which is tipped in black, is non-prehensile. It is used for maintaining balance when leaping on branches and moving on hands and feet through the different levels of the forest. Males weigh about 1.8 pounds (0.8 kilograms). Females are slightly smaller. The monkeys measure 9.5 to 18.5 inches (24 to 47 centimeters) with a tail length of 8.7 to 16.5 inches (22 to 42 centimeters).

Geographic range: Three-striped night monkeys are found in Brazil, Colombia, and Venezuela.

Habitat: Three-striped night monkeys inhabit different types of forests, including evergreen forests, wet and dry forests, and forests along rivers. They prefer forests with thick, tangled vines and thickets for cover during sleep or rest. They also thrive near human developments.

Diet: Three-striped night monkeys feed mainly on fruits, supplementing them with insects, tree frogs, nectar, and leaves.

Behavior and reproduction: Three-striped night monkeys live in family groups in forest trees. A typical family consists of the parents and their infant and juvenile offspring. The family forages at night, staying up longer on moonlit nights. They travel through the same areas of the trees, which is especially helpful in finding their way in the dark. They usually move on all fours, but can jump from tree to tree. During the day, they share a sleeping site among tangled vines, dense vegetation, or in a tree hollow.

Mothers give birth to a single infant annually, although they may have twins, but very rarely. Fathers are the principal caregivers, carrying the infant starting from birth. They play with the infant and older offspring, guard them against predators, and also teach them. The infant is given to the mother only during nursing. The mother does not participate in play and gives the infant back to the father immediately after it is fed. The infant is weaned by eight months of age. Older offspring help the father care for the newborn. The young stay with the family for up to three years, leaving peacefully on their own.

Three-striped night monkeys are territorial, advertising their ownership with secretions from scent glands in the chest and the tail base. They also use urine for scent marking. They soak their fur and the soles of their feet with urine, which gets transferred to leaves, branches, and trunks. They are loud creatures, announcing their presence with different types of sounds. They use an owl-like hoot when ready to mate or when separated while foraging in the dark. They whoop and grunt to threaten intruders, and trill when greeting each other. Hostile physical communications include back-arching, furraising, defecating, and urinating.

Three-striped night monkeys and people: Three-striped night monkeys are hunted for food by native people. They are also trapped and sold as pets. These monkeys have been found to be carriers of the human malaria parasites. They are especially valued for research in the development of drugs used for treatment and prevention of malaria.

Conservation status: The three-striped night monkey is not a threatened species. ∎

FOR MORE INFORMATION

Books:

Kavanagh, Michael. A Complete Guide to Monkeys, Apes and Other Primates. New York: The Viking Press, 1983.

Kinzey, Warren G., ed. New World Primates: Ecology, Evolution, and Behavior. New York: Aldine de Gruyter, 1997.

Napier, John R., and Prue H. Napier. The Natural History of the Primates. Cambridge, MA: The MIT Press, 1986.

Nowak, Ronald M. Walker's Primates of the World. Baltimore: The Johns Hopkins University Press, 1999.

Web sites:

"Aotus trivirgatus (Northern Gray-Necked Owl Monkey)." The Primate Foundation of Panama. http://www.primatesofpanama.org/academicresources/articles/monoculture/atrivirgatus.htm (accessed on July 6, 2004).

The Squirrel Monkey Breeding and Research Resource. "Aotus Natural History." University of South Alabama Department of Comparative Medicine. http://www.saimiri.usouthal.edu/aotus_natural_history.htm (accessed on July 6, 2004).