The six species of howler monkeys are among the largest of the American or New World monkeys. Head and body length is 22-36 inches; tail length is 23-36 inches; and adults weigh from 9-22 pounds. Their hair is coarse and their faces are naked. Males are usually visibly larger than females. As the name suggests, they are black in color.

While the male of the species is black, the female is not; she is brown in color. 

Many experts believe this is a survival strategy, helping the female to blend into the colors of the forest.  Offspring are brown when born, no matter what their sex.  As they mature the male's fur turns black.

Lower jaws and necks are quite large. Legs are shorter and stouter than those of the spider monkeys. The powerful prehensile tails are naked on the underside.

The angle of their lower jaws makes it possible for the animals to produce their remarkable loud resonant sounds for which these primates are especially noted. The loud and persistent calls have been heard by people almost two miles away through jungle growth and over three miles away across lakes.

DISTRIBUTION AND HABITAT:

Howler Monkeys are inhabitants of New World rain forests. Black Howlers range through eastern Bolivia, southern Brazil and Paraguay, and northern Argentina.

BEHAVIOR:

Troop size varies from 3-19; groups usually include 1-3 adult males and 2-7 adult females. They live and travel in these small troops and sleep high in the trees at night. About 75% of their time is spent resting, 20% feeding, and 5% with social activities.

DIET: They are reported to eat more leaves than any other New World monkey. They also enjoy fruits, including figs, and other plant parts.

REPRODUCTION and GROWTH:

In Black Howler Monkeys, sexual maturity is achieved at five years by males, and at 3-4 years by females. But often the young animals lack the social maturity to be allowed to mate for several more years.

Gestation is 180-194 days and single births are usual. Babies cling to their mothers' fur, and as the babies get older they make their permanent riding positions on the mothers' backs. This continues for about a year. Older males sometimes kill the young.

Young are weaned at around 10 months of age and the young disperse from their natal group upon adulthood.

Average life span is about 16 years in the wild. Maximum longevity is over 20 years.