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Howler monkeys (genus Alouatta) are the largest New World monkeys. They are the loudest land animal, producing howls that can be heard up to three miles away. Fifteen species and seven subspecies of howler monkey are currently recognized.
Fast Facts: Howler Monkey
- Scientific Name: Alouatta
- Common Names: Howler monkey, New World baboon
- Basic Animal Group: Mammal
- Size: Head and body: 22-36 inches; tail: 23-36 inches
- Weight: 15-22 pounds
- Lifespan: 15-20 years
- Diet: Omnivore
- Habitat: Central and South American forests
- Population: Decreasing
- Conservation Status: Least Concern to Endangered
Like other New World monkeys, howler monkeys have wide side-set nostrils and furred prehensile tails with naked tips that help the primates grip tree branches. Howler monkeys have beards and long, thick hair in shades of black, brown, or red, depending on sex and species. The monkeys are sexually dimorphic, with males 3 to 5 pounds heavier than females. In some species, such as the black howler monkey, mature males and females have different coat colors.
Howler monkeys are the largest New World monkeys, with head and body length averaging 22 to 36 inches. One characteristic of the species is its extremely long, thick tail. The average tail length is 23 to 36 inches, but there are howler monkeys with tails five times their body length. Adults weigh between 15 and 22 pounds.
Like humans, but unlike other New World monkeys, howlers have trichromatic vision. Both male and female howler monkeys have an enlarged hyoid bone (Adam's apple) that helps them make extremely loud calls.Males and females are different colors in some howler monkey species. Tier Und Naturfotografie J und C Sohns / Getty Images
Habitat and Distribution
Howler monkeys live in the tropical forests of Central and South America. They spend their lives in the tree canopy, only rarely descending to the ground.Howler monkey distribution. Miguelrangeljr & IUCN / Creative Commons Attribution-Share Alike 3.0 Unported License
The monkeys primarily forage tree leaves from the upper canopy, but also eat fruit, flowers, nuts, and buds. They sometimes supplement their diet with eggs. Like other mammals, howler monkeys cannot digest cellulose from leaves. Bacteria in the large intestine ferment cellulose and produce nutrient-rich gases which the animals use as an energy source.
Obtaining energy from leaves is an inefficient process, so howler monkeys are generally slow-moving and live within relatively small home ranges (77 acres for 15 to 20 animals). Males vocalize at dawn and dusk to identify their position and communicate with other troops. This minimizes conflict over feeding and sleeping grounds. Troop ranges overlap, so howling lessens the need for males to patrol territories or fight. Each troop consists of six to 15 animals, usually containing one to three adult males. Mantled howler monkey troops are larger and contain more males. Howler monkeys rest in the trees about half of the day.
Reproduction and Offspring
Howler monkeys reach sexual maturity around 18 months of age and display sexual readiness by tongue-flicking. Mating and birth may occur at any time of the year. Mature females give birth every two years. Gestation is 180 days for the black howler monkey and results in a single offspring. At birth, both male and female black howler monkeys are blond, but males turn black at two and a half years of age. In other species the color of the young and adults is the same for both sexes. Adolescent males and females leave their parents' troop to join unrelated troops. The average life expectancy of a howler monkey is 15 to 20 years.
Howler monkey IUCN conservation status varies according to species, ranging from least concern to endangered. The population trend is unknown for some species and decreasing for all others. Howler monkeys are protected in parts of their range.
The species faces multiple threats. Like other New World monkeys, howlers are hunted for food. They face habitat loss and degradation from deforestation and land development for residential, commercial, and agricultural use. Howler monkeys also face competition from other species, such as spider monkeys and woolly monkeys.
Howler Monkeys and Humans
Howler monkeys are not aggressive toward humans and are sometimes kept as pets despite their loud vocalizations. Some Mayan tribes worshiped howler monkeys as gods.
- Boubli, J., Di Fiore, A., Rylands, A.B. & Mittermeier, R.A. Alouatta nigerrima. The IUCN Red List of Threatened Species 2018: e.T136332A17925825. doi:10.2305/IUCN.UK.2018-2.RLTS.T136332A17925825.en
- Groves, C.P. Order Primates. In: D.E. Wilson and D.M. Reeder (eds), Mammal Species of the World, pp. 111-184. The Johns Hopkins University Press, Baltimore, Maryland, USA, 2005.
- Neville, M. K., Glander, K. E., Braza, F. and Rylands, A. B. The howling monkeys, genus Alouatta. In: R. A. Mittermeier, A. B. Rylands, A. F. Coimbra-Filho an G. A. B. da Fonseca (ed.), The Ecology and Behavior of Neotropical Primates, Vol. 2, pp. 349-453, 1988. World Wildlife Fund, Washington, DC, USA.
- Sussman, R. Primate Ecology and Social Structure, Vol. 2: New World Monkeys, Revised First Edition. Pearson Prentice Hall. pp. 142-145. July, 2003. ISBN 978-0-536-74364-0.