Howler monkeys (genus Alouatta monotypic in subfamily Alouattinae) are among the largest of the New World monkeys. Nine species are currently recognised. Previously classified in the family Cebidae, they are now placed in the family Atelidae. These monkeys are native to South and Central American forests. They live in groups of usually about 18 individuals. Threats to howler monkeys include being hunted for food and captivity.
Their name comes from their distinctive loud barking whoop they make, which can be heard over considerable distances. William Henry Hudson
pointed out in his novel Green Mansions
, "howler" is a misnomer since the male's voice sounds rather like a powerful roar; female vocalisations sound like a pig's grunt.
Howlers are called "congos" in Nicaragua and Costa Rica. In Belize they are called "baboons", although they are not closely related to the genus Papio, which usually carries that name.
- Family Atelidae
- Subfamily Alouattinae
- A. palliata group
- A. seniculus group
- A. caraya group
- Subfamily Atelinae
Anatomy and physiology
Howler monkeys have a short snout, and wide-set, round nostrils. They range in size from 56 to 92 cm, excluding their tail which can be equally as long. Like many New World monkeys, they have prehensile tails
. Unlike other New World monkeys, both male and female howler monkeys have trichromatic
colour vision. This has evolved independently
from other New World monkeys due to gene duplication
. They have a lifespan of 15 to 20 years.
They move quadrapedally and do not brachiate
, usually holding on to a branch with at least two hands or one hand and the tail at all times. Their prehensile tails are strong enough to support the monkey's entire body weight, although they seldom do so. The first 2 fingers
of each hand are set apart and are opposable to the other three. They very seldom leave the trees. They rest about 80 percent of the time and are considered the least active of all monkeys.
Howler monkeys live in groups where the number of females is greater than the number of males. Groups may have only one male or several males. Unlike most New World monkeys, juveniles of both genders emigrate from their natal groups, so neither adult males nor adults females in a group are typically related. Fighting among group members is infrequent and generally of short duration. However, serious injuries can result. Both males and females may fight with each other. Group size varies by species and by location, with an approximate male to female ratio of a male to four females.
As their name suggests, vocal communication
forms an important part of their social behavior
. They have an enlarged basihyal or hyoid bone
which helps them make their loud sound. They are considered the loudest land animal. According to Guinness Book of World Record it can be heard clearly for 3 miles.
Diet and feeding
These large, slow moving monkeys are the only folivores
of the New World monkeys. Howlers eat mainly top canopy leaves
, together with fruit
, buds, flowers
, and nuts
. They need to be careful not to eat too much of certain species of mature leaf in one sitting, as some of the leaves they eat contain toxins that can poison the monkey.
Relationship with humans
While seldom aggressive, howler monkeys do not take well to captivity and are of surly disposition, and hence are the only monkey in their forests not made a pet by the Native Americans . However, the Black Howler (Alouatta caraya) is a relatively common pet monkey in contemporary Argentina due to its gentle nature, in comparison to the capuchin monkey's aggressive tendencies, in spite of its lesser intelligence as well as the liabilities meant by the size of its droppings and the males' loud vocalisation.
Alexander von Humboldt said about howler monkeys that "their eyes, voice, and gait are indicative of melancholy", while John Lloyd Stephens described those at the Maya ruins of Copán as "grave and solemn as if officiating as the guardians of consecrated ground". To the Mayas of the Classic Period, they were the divine patrons of the artisans, especially scribes and sculptors. Copán in particular is famous for its representations of Howler Monkey Gods. Two howler monkey brothers play a role in the 16th century myth of the Maya Hero Twins included in the Popol Vuh.