Alouatta seniculus (*)
Alouatta seniculus, (Linnaeus, 1766)
The Red Howler Monkey (Alouatta seniculus) is a South American species of howler monkey, a type of New World monkey. It is found in the western Amazon Basin in Venezuela, Colombia, Ecuador, Peru, Bolivia and Brazil. The population in the Santa Cruz Department in Bolivia was split off as a separate species, the Bolivian Red Howler, in 1985, and more recently it has been recommended splitting off the population in north-eastern South America and Trinidad as the Guyanan Red Howler. All howler monkeys belong to the family Atelidae and the infraorder Platyrrhini (New World monkeys).
There is little sexual dimorphism. The males range from 49-72 cm and females from 46-57 cm long. The males weigh between 5.4-9 kg, while females are 4.2-7 kg. It has a long prehensile tail of approximately 49-75 cm. The tail is covered with fur except for the last third underside of the tail, which allows it to grab branches. The color of both males and females is a deep reddish-brown, and the color shade changes with age. Their faces are surrounded by fur and they have stubby noses.
The jawbone of the red howler monkey is large, especially the body of the mandible. The position of the foramen magnum is very posterior in the howler monkey, making way for the expanded jaw and enflated hyoid bone. Howler monkeys also have an inflated bulla, which is the bony encasement of the middle ear. This makes them an exception among other New World monkeys.
Alouatta seniculus is an arboreal and diurnal primate that spends much of its time up high in the canopy. Its preferred method of locomotion is quadrupedal walking with minimal leaping. Their long, prehensile tails also assist them with this by providing both support and grasping abilities. In addition, their hands and feet have a grasping pattern that allows them to better move about in the trees. This can be seen in their hands by the wide separation of the second and third digits.
It lives in groups of 3 to 9 individuals (usually 5 to 7). The groups are polygynous with only one or two males and the rest females and their offspring. One male is the usually dominant monkey of the group, and he is responsible for leading them to new food sites and defending them. The females of the group are in charge of the offspring. Venezuelan Red Howlers are most active in the morning; this is when the group is on the move to find another feeding spot. The howlers are famous for their “dawn chorus”. These sounds are roaring and howling calls that are performed mostly by the males in the group. The roars can be heard up to 5 km away in the forest, and makes their presence known in the area. This is also used to prevent confrontations between groups, which will prevent energy loss by avoiding physical fighting. Because of their low-sugar diets, conservation of energy is key to their day. The calls also help in the scattering of the groups and lessens the competition over food.
Diet and dentition
Howler monkeys are folivores which means that their diet mainly consists of leaves, but they also rely on nuts, small animals, fruits, seeds, and flowers for important sources of nutrition. These foods provide sugar necessary for growth and energy for the monkeys. The most important part of their diet are leaves, which they can’t live without for more than a week. They eat both older and younger leaves; however, the older leaves provide more nutrition. The howler monkeys are able to eat their largely leafy diet of fibrous leaves due to the structural aspects of their dentition. Narrow incisors aid in the ingestion of the leaves, and molars with sharp, shearing crests help them to better chew their food. In addition, they have a complex stomach that aids in the digestive process. Their hindgut and large intestine also help with digestion. The hindgut contains bacteria that digest leaves and makes up a third of the Venezuelan Red Howler’s total body volume.
Like other New World monkeys, the red howler monkey's dental formula (maxilla and mandible) is as follows: 2 Incisors, 1 Canine, 3 Premolars, 3 Molars.
There is fierce sexual competition between males due to an unbalanced sex ratio. The females attract males by moving their tongue around in order to initiate mating. If the male does not respond, she moves on to another mate. The average gestation period is 190 days. The infant will stay with the mother for 18-24 months. After males reach sexual maturity they are expelled from their natal group. The male must then invade a foreign group. There, the male kills off the other leader and whatever offspring the first leader generated. By doing this, the male is killing any possible competition. Less than 25% of offspring survive male invasions.
There are traditionally three subspecies of this howler, though Stanyon et al. (1995) concluded that the number of chromosomal differences between A. s. sara and A. s. arctoidea (which resulted in A. s. sara being a considered a full species) was on a similar scale to that found between A. s. sara and A. s. seniculus by Minezawa et al. (1986).
* Colombian Red Howler, Alouatta seniculus seniculus
* Heatwole, Alan M.. Monkeys and Apes. 1st. New York: Gallery Books, 1990.
Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License