Red howlers are the biggest of the howler monkeys. This monkey has thick, brownish to dark red fur, with gold or bright orange underparts, the color varying with the age and where the animal lives. The naked dark face is surrounded by fur. They have a somewhat stubby nose and their wide jaw is covered in a thick beard. An enlarged hyoid bone in the mouth at the base of the tongue causes the throat to look swollen. Males are bigger and their beard is darker and heavier. Their tails are very long and without fur on the underneath of the last third, providing better grip for holding onto branches.
Red howler monkeys live throughout northwestern South America, in Bolivia, Brazil, Colombia, Ecuador, Guyana, French Guiana, Venezuela, Peru, Suriname, the island of Trinidad and other South American countries. They favor the canopy of tropical deciduous forests and rainforests, and particularly like Cecropia and teak trees.
Red howlers form groups of between 1 to 3 males with 2 to 7 females and different numbers of juveniles. Males in bachelor groups from time to time try to gain the control of a group with females by fighting the lead male. Males wake up the forest early in the morning by howling loudly, being audible as far as 2 miles (5 km) distant. They also howl at night before sleeping, being answered by males in other red howler groups, letting them know where they are so that there is no overlapping of territories. Red howlers are most active during the morning, when groups move about looking for a feeding spot. They dislike rain, and howl when it is raining, sitting hunched over in trees. They usually stay high up in trees in order to find the most leaves.
Red howler monkeys eat flowers, leaves and fruit, leaves being up to 60% of their consumption. Howlers are selective eaters, avoiding leaves that are poisonous or unsafe. They favor young tender leaves, being easier to digest and having more protein and sugar.
Red howler monkeys are polygynous, one male mating with multiple females. The female usually invites courtship by sticking out her tongue at a male. If there is no response, she approaches another male. Mating takes place throughout the year, gestation is for 6 months and one baby is born. At one month, infants are able to use their tail to cling on to their mother, riding on her back, until they are one year old. Nursing lasts until the young are between 18 and 24 months old. Males can be very affectionate with the infants, though only with their direct offspring. Males are sexually mature after 5 years and females at 4 years old.
Habitat destruction is the biggest threat. Because they live in seasonally flooded forests, they can be adversely affected by both damming of rivers and logging along them. Red howlers are sometimes killed for the sake of their enlarged hyoid, to be used as a drinking vessel in the treatment of goiters, or for food, and can be commercially exported.
The IUCN Red List and other sources don’t provide the number of the Red howler monkey total population size. Currently this species is classified as Least Concern (LC) on the IUCN Red List.