The Howler Monkey
Howler monkeys (genus Alouatta monotypic in subfamily Alouattinae) are among the largest of the New World monkeys. Fifteen 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. Threats to howler monkeys include human predation, habitat destruction and being captured for captivity as pets or zoo animals.
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. They have prehensile tails. Both male and female howler monkeys have trichromatic colour vision. This has evolved due to gene duplication. They have a lifespan of 15 to 20 years. Howler species are dimorphic and can also be dichromatic. Males are, on average, 1.5 to 2 kg heavier than females.
Howler monkeys generally move quadrupedally on the tops of branches, usually grasping a branch with at least two hands or one hand and the tail at all times. They have strong prehensile tails which are able to support the monkey’s entire body weight. However, fully adult howler monkeys do not often rely on their tail for full body support whereas juveniles do so more frequently.
Most howler monkey species live in groups of 10 to 15 animals, with one to three adult males and multiple females. Mantled howler monkeys are an exception, commonly living in groups of 15 to 20 individuals with more than three adult males. Unlike most New World monkeys, in which one sex remains in natal groups, juveniles of both sexes emigrate from their natal groups, such that howler monkeys could spend the majority of their adult lives in association with non-kin.
Physical 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 but physical aggression is even rarer between sexes. 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 behaviour. They have an enlarged basihyal or hyoid bone which helps them make their loud vocalizations. Group males generally call at dawn and dusk as well as interspersed times throughout the day. The main vocals consist of loud, deep guttural growls or “howls.”
Howler monkeys are widely considered to be the loudest land animal. According to Guinness Book of World Records, their vocalizations can be heard clearly for 3 miles (4.8 km). It is hypothesized that the function of howling relates to intergroup spacing and territory protection, as well as possibly mate-guarding.
Diet and feeding
These large and 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. Howler monkeys are also known to occasionally raid birds’ nests and chicken coops and consume the eggs.
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”.
(Source: Wikipedia, the free encyclopedia)