Howler monkey

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Howler monkeys [1]
Alouatta guariba.jpg
Brown howler monkey
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Atelidae
Subfamily: Alouattinae
Trouessart, 1897 (1825)
Genus: Alouatta
Lacepede, 1799
Type species
Simia belzebul
Linnaeus, 1766

See text

Alouatta range map.png
Brown Howler Monkeys distribution
  • MycetesIlliger, 1811
  • StentorÉ. Geoffroy, 1812

Howler monkeys (genus Alouatta, monotypic in subfamily Alouattinae) are among the largest of the New World monkeys. They are famous for their loud howls, which can travel more than one mile through dense rain forest. These monkeys are native to South and Central American forests. Threats include human predation, habitat destruction, and capture for pets or zoo animals. Fifteen species are recognized. Previously classified in the family Cebidae, they are now placed in the family Atelidae.



Anatomy and physiology

Male mantled howler Allouataadulto 500px.jpg
Male mantled howler

Howler monkeys have short snouts and wide-set, round nostrils. Their noses are very keen, and they can smell out food (primarily fruit and nuts) up to 2 km away. Their noses are usually roundish snout-type, and the nostrils have many sensory hairs growing from the interior. They range in size from 56 to 92 cm (22 to 36 in), excluding their tails, which can be equally long; in fact in some cases the tail has been found to be almost five times the body length.[ citation needed ] This is a prime characteristic. Like many New World monkeys, they have prehensile tails, which they use while picking fruit and nuts from trees. 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 lifespans of 15 to 20 years. Howler species are dimorphic and can also be dichromatic (i.e. Alouatta caraya). Males are typically 1.5 to 2.0 kg heavier than females.

The hyoid of Alouatta is pneumatized, one of the few cases of postcranial pneumaticity outside the Saurischia. The volume of the hyoid of male howler monkeys is negatively correlated with the dimensions of their testes. [4]


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. Their strong prehensile tails are able to support their entire body weight. Fully grown adult howler monkeys do not often rely on their tails for full-body support, but juveniles do so more frequently.


A Bolivian red howler (Alouatta sara) Alouatta sara (Bolivian red howler).jpg
A Bolivian red howler (Alouatta sara)

Social systems

Most howler species live in groups of six 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. The number of males in a given group is inversely correlated with the size of their hyoids and is positively correlated with testes size. This results in two distinct groups, wherein one male with a larger hyoid and smaller testes copulates exclusively with a group of females. The other group has more males, which have smaller hyoids, and larger testes, and free copulation occurs among the group. The larger the number of males, the smaller the hyoid, and the larger the testes. [4] Unlike most New World monkeys, in which one sex remains in natal groups, juveniles of both sexes emigrate from their natal groups, [5] such that howler monkeys could spend the majority of their adult lives in association with unrelated monkeys.

Physical fighting among group members is infrequent and generally of short duration, but serious injuries can result. Both males and females rarely fight with each other, but physical aggression is even more rare between sexes. [5] [6] Group size varies by species and by location, with an approximate ratio of one male to four females. [5]


A pair of black howler monkeys (Alouatta caraya) vocalising Howler monkey.jpg
A pair of black howler monkeys (Alouatta caraya) vocalising

As their name suggests, vocal communication forms an important part of their social behavior. They each 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. Their main vocals consist of loud, deep, guttural growls or "howls". Howler monkeys are widely considered to be the loudest land animals. According to Guinness Book of World Records, their vocalizations can be heard clearly for 3 mi (4.8 km). [7] The function of howling is thought to relate to intergroup spacing and territory protection, as well as possibly to mate-guarding.

Diet and feeding

An ursine howler Ursine howler monkey (Alouatta seniculus arctoide) 2.jpg
An ursine howler

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 many leaves of certain species in one sitting, as some contain toxins that can poison them. [8] Howler monkeys are also known to occasionally raid birds' nests and chicken coops and consume the eggs. [9]

Relationship with humans

While they are not usually aggressive, Brown howler monkeys do not take well to captivity and are of bad-tempered and unfriendly disposition. However, the Black howler monkeys (Alouatta caraya) is a relatively common pet 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 of the size of its droppings and the male monkey’s loud vocalisations.

John Lloyd Stephens described the howler monkeys at the Maya ruins of Copán as "grave and solemn, almost emotionally wounded, 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. They were seen as gods in some tribes, and the long, sleek tail was worshipped for its beauty. Copán, in particular, is famous for its representations of howler monkey gods. Two howler monkey brothers play a role in the myth of the Maya Hero Twins included in the Popol Vuh , a widely feared tale of soul and passion.

Related Research Articles

New World monkey Parvorder of mammals

New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboidea, the only extant superfamily in the parvorder Platyrrhini.

Atelidae Family of New World monkeys

The Atelidae are one of the five families of New World monkeys now recognised. It was formerly included in the family Cebidae. Atelids are generally larger monkeys; the family includes the howler, spider, woolly, and woolly spider monkeys. They are found throughout the forested regions of Central and South America, from Mexico to northern Argentina.

Colombian red howler Species of monkey

The Colombian red howler or Venezuelan red howler is a South American species of howler monkey, a type of New World monkey, found in the western Amazon Basin in Venezuela, Colombia, Ecuador, Peru and Brazil. The population in the Santa Cruz Department in Bolivia was split off as a separate species, the Bolivian red howler, in 1986, and more recently, splitting off the population in northeastern South America and Trinidad as the Guyanan red howler has occurred. All howler monkeys belong to the family Atelidae and the infraorder Platyrrhini.

Brown howler Species of New World monkey

The brown howler, also known as brown howler monkey, is a species of howler monkey, a type of New World monkey that lives in forests in southeastern Brazil and far northeastern Argentina (Misiones). It lives in groups of two to 11 individuals. Despite the name "brown howler", it is notably variable in colour, with some individuals appearing largely reddish-orange or black.

Black howler Species of New World monkey

The black howler or black-and-gold howler, is among the largest New World monkeys and a member of the Alouatta genus. The black howler is distributed in areas of South America such as Paraguay, southern Brazil, eastern Bolivia, northern Argentina, and Uruguay. This species is sexually dimorphic, with adult males having entirely black fur and adult females and babies of both sexes having an overall golden colouring; which emphasizes black-and-gold in the name. The IUCN Red List has classed the black howler as Near Threatened as a result of a recent population reduction due to a variety of human-caused factors.

Red-handed howler Species of New World monkey

The red-handed howler is a vulnerable species of howler monkey, a type of New World monkey. It is endemic to Brazil, found in the southeastern Amazon and disjunctly in the Atlantic Forest between Rio Grande do Norte and Sergipe.

Bolivian red howler Species of mammal

The Bolivian red howler is a species of howler monkey, a type of New World monkey, endemic to Bolivia. It can be found in rain forests, including riverine and seasonally flooded forests.

Mantled howler Species of New World monkey

The mantled howler is a species of howler monkey, a type of New World monkey, from Central and South America. It is one of the monkey species most often seen and heard in the wild in Central America. It takes its "mantled" name from the long guard hairs on its sides.

Yucatán black howler Species of New World monkey

The Yucatán black howler, or Guatemalan black howler, is a species of howler monkey, a type of New World monkey, from Central America. It is found in Belize, Guatemala and Mexico, in and near the Yucatán Peninsula. It lives in evergreen, semideciduous and lowland rain forests. It is also known as the baboon in Belize, although it is not closely related to the baboons in Africa.

The Coiba Island howler is a type of howler monkey, a type of New World monkey, endemic to Panama. Although the Coiba Island howler has been recognized as a separate species by a number of authorities since a 1987 study of its fingerprints, mitochondrial DNA testing found it does not differ from mantled howler populations in any significant way. A reason given for treating it as a separate species is that the dermal ridges of its hands and feet differ from those of the mantled howler.

Evolution of color vision in primates Loss and regain of colour vision during the evolution of primates

The evolution of color vision in primates is highly unusual compared to most eutherian mammals. A remote vertebrate ancestor of primates possessed tetrachromacy, but nocturnal, warm-blooded, mammalian ancestors lost two of four cones in the retina at the time of dinosaurs. Most teleost fish, reptiles and birds are therefore tetrachromatic while most mammals are strictly dichromats, the exceptions being some primates and marsupials, who are trichromats, and many marine mammals, who are monochromats.

Sexual dimorphism in non-human primates

Sexual dimorphism describes the morphological, physiological, and behavioral differences between males and females of the same species. Most primates are sexually dimorphic for different biological characteristics, such as body size, canine tooth size, craniofacial structure, skeletal dimensions, pelage color and markings, and vocalization. However, such sex differences are primarily limited to the anthropoid primates; most of the strepsirrhine primates and tarsiers are monomorphic.

The Azuero howler a type of monkey that is a subspecies of the Coiba Island howler A. coibensis. This subspecies is endemic to the Azuero Peninsula in Panama. The Azuero howler is distinguished primarily by its golden flanks and loins, and browner appearance on the rest of its body.

Ecuadorian mantled howler Subspecies of New World monkey

The Ecuadorian mantled howler is a subspecies of the mantled howler, A. palliata. It ranges from Panama through Colombia and Ecuador into northern Peru. The range limits between the Ecuadorian mantled howler and the golden-mantled howler are not entirely clear. The Ecuadorian mantled howler replaces the Golden-mantled howler in either extreme eastern Costa Rica or western Panama. The Ecuadorian mantled howler differs from the golden-mantled howler primarily by being paler, with a more yellowish mantle.

Golden-mantled howler Subspecies of New World monkey

The golden-mantled howler is a subspecies of the mantled howler, A. palliata. It ranges throughout much of Central America, in Guatemala, Honduras, Nicaragua and Costa Rica, and possibly Panama. The range limits between the golden-mantled howler and the Ecuadorian mantled howler are not entirely clear. The Ecuadorian mantled howler replaces the golden-mantled howler in either extreme eastern Costa Rica or western Panama.

Mexican howler Subspecies of New World monkey

The Mexican howler is a subspecies of the mantled howler, A. palliata. This subspecies is found predominantly in forests between south eastern Mexico and north eastern Peru. Typical of its species, the Mexican howler monkey has a prehensile tail, a deep jaw, and a large pharynx which it uses to make characteristically deep and resonating howls. Mantled howler monkeys are known for forming unusually large cohorts averaging 14 members and sometimes extending to 40 members.

Southern brown howler Subspecies of New World monkey

The southern brown howler is a monkey subspecies of brown howler native to southeastern Brazil and far northeastern Argentina (Misiones). Gregorin, 2006, considered the southern brown howler to be a separate species, Alouatta clamitans, but this has not been universally accepted.

Northern brown howler Subspecies of New World monkey

The northern brown howler is the type subspecies of the brown howler, native to Brazil. It is listed as critically endangered, with fewer than 250 individuals restricted to the vicinity of the Jequitinhonha River. The species feeds on fruits, flowers, and by preference immature leaves which are easier to digest than mature leaves; foraging for these foods in hillside habitats was shown to require more energy expenditure than in valley habitats.


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