This primate lives up to an elevation of 2,500 m from southern Mexico to northwestern South America.

Adults are black with brown or blonde saddles; infants are silver to golden brown and become increasingly like adult coloration until they are about 12 weeks old.

Howlers are famous for the incredible vocalizations made by adult males. Their howls can be heard more than 1 km away through the forest. They often make calls at sunrise and sunset or in response to people, airplanes, rain and thunder, or other howlers. Some biologists conclude that the howling is used as a spacing mechanism between individuals or to communicate within the troop.

The group is usually defined as several adult males and females, with their juveniles and infants, although juveniles usually leave their parents' group eventually. At 12 weeks old, howlers may move away from their parents. A female will become sexually active at 3 years, and have her first infant before her fourth year, with a gestation period of 6 months. Within a group, all adult males are dominant to all adult females, but the youngest adult of either sex holds the alpha rank for that sex. Average group size varies from 11 to 18 depending on the region. Howlers hardly ever descend to the ground except to travel between islands of trees in a habitat.

These primates are sedentary foragers: they eat mostly leaves, but they may also pick fruits and flowers. Since they are not dependent on only eating fruit (as spider monkeys do), howlers can survive in daily and home ranges rather small for a primate of their size. They are very choosy eaters, and often only eat certain parts of an individual tree and other parts of a different tree. From one tree they may choose mature leaves, young leaves, flowers, the petioles or the pulvinus of leaves. They also seem to base their food choices on how much the plant contains protein, fiber, and levels of alkaloids and tannins. Essentially, they try to maximize protein and amino acids in their diet but minimize their intake of fiber and plant secondary compounds.

An adult male howler can weigh up to 6 to 7 kg; an adult female will generally be 4 to 5 kg. Howlers have tails longer than their head and body length. Infant howlers are about 0.4 kg at birth.

Order: Primates
Family: Cebidae

Eisenberg, John. Mammals of the Neotropics, Vol. 1. The University of Chicago Press: Chicago, 1989.

Glander, K. E. in Janzen, Daniel H. Costa Rican Natural History. Chicago: University of Chicago Press, 1983.

Wilson, D. E. in Janzen, Daniel H. Costa Rican Natural History. Chicago: University of Chicago Press, 1983.

-Amy Strieter, Wildlife Writer