Howler monkey

Male howler monkey

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 color vision.[2] This has evolved independently from other New World monkeys due to gene duplication.[3] They have a lifespan of 15 to 20 years. Howler species are dimorphic and can also be dichromatic (i.e. Alouatta caraya). Males are, on average, 1.5 to 2 kg heavier than females.

The hyoid of Alouatta is pneumatized -- one of the few cases of postcranial pneumaticity outside Saurischia.
Locomotion
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.

Communication

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 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.[6] Howler monkeys are also known to occasionally raid birds nests and chicken coops and consume the eggs

Relationship with human

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[citation needed]. 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.