Brown howling monkey (Alouatta guariba)

Brown howling monkey eating fruit
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Brown howling monkey fact file

Brown howling monkey description

GenusAlouatta (1)

Brown howling monkeys, like other howler monkeys, are best known for their impressive howls, which can be heard for over 1.6 km and are often mistaken for roars of lions by visitors to the area (2). Far from being dangerous predators, these primates are placid, arboreal vegetarians that live in social groups (2). There are ten species of howler monkeys, which can be identified by their coat colour (2) (3). As expected, brown howling monkeys have brown coats, though the colour may vary from brown to dark red or black. The hair is lighter and sparser on the belly, and the face and ears are dark and bare (2). Like other howlers, they have large stocky frames. The males are considerably larger than the females. Their tails are long and prehensile, and lack fur on the underside near the tip. These amazing features allow brown howling monkeys to hang from their tails and use them as an anchor while feeding (2) (3).

Also known as
brown howler monkey, red and black howler, southern brown howling monkey.
Alouatta fusca.
Hurleur Brun.
Barbado, Bugio, Guariba.
Female head/body length: 45-49 cm (2)
Male head/body length: 54-59 cm (2)
Male tail length: 52 – 67 cm (3)
Female tail length: 48 – 57 cm (3)
Male weight: 5.3-7.15 kg (2)
Female weight: 4.1-5.0 kg (2)

Brown howling monkey biology

The biology and behaviour of these primates has fascinated scientists over the years. Charles Darwin suggested that, within the vertebrates, the loudest male would attract the most females by advertising his strength (2). However, there seems little evidence of this in howler monkeys and it is now thought that their calls announce a troop’s right to food trees in the forest. Unlike other howlers, this species does not give a dawn chorus and seems to reserve most of its howling for inter-group encounters (5). These loud calls therefore play a role in avoiding conflict between groups and thus in saving energy which can be better used for foraging and digestion (2)

Brown howling monkeys feed mainly on leaves, flowers and fruit, though the composition of their diet varies according to the season and their location in the forest (6). During autumn and winter, individuals must also spend more time feeding due to the inferior quality of the food and the higher demands on energy in these colder months (6). Generally howlers spend over half of their waking hours resting to conserve energy for feeding. Though leaves, flowers and fruit are abundant in tropical forests, they are low in nutrients and high in cellulose and so do not provide much energy (2). Mammals lack the enzymes to digest cellulose, and while primates of the subfamily Colobinae have evolved specialised stomachs containing bacteria to digest the leaves, howlers have a simple, acid stomach similar to that of humans. However, howlers also have two enlarged sections where fermentative bacteria exist that are able to break down the material efficiently (2). In the process of fermentation, energy-rich gases (known as volatile fatty acids) are produced. Howlers absorb and use these gases as an energy source for their daily activities (2).

Home ranges are small, up to around 31 hectares for a group of 15-20 individuals, as brown howling monkeys limit the distances they travel to feed (2). Males defend the home ranges by intimidation and fighting, which protects the group and allows females to invest more energy in reproduction and care of the young (2). Females usually have a single offspring, which are weaned before they are one year old (6).


Brown howling monkey range

Found in south-eastern Brazil and north-eastern Argentina in South America, and possibly in parts of Uruguay and Bolivia as well (3).


Brown howling monkey habitat

Inhabits primary and secondary Atlantic coastal forest and often associated with ‘monkey puzzle’ trees (Araucaria) – an endemic species of pine (2) (3).


Brown howling monkey status

Classified as Least Concern (LC) on the IUCN Red List (1), and listed on Appendix II of CITES (4). Two subspecies are recognised: the northern brown howler monkey (Alouatta guariba guariba) is classified as Critically Endangered (CR) and the southern brown howler monkey (Alouatta guariba clamitans) is classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern


Brown howling monkey threats

Although the IUCN Red List classifies this species is Near Threatened (NT) overall, the nominate subspecies, the northern brown howling monkey (Alouatta guariba guariba), is classified as Critically Endangered (1). The species’ populations are extremely fragmented and reduced due to habitat destruction and development in the coastal forests of south-eastern Brazil and north-eastern Argentina (1) (3). Unlike many other primates, members of this genus are actually better able to survive in small isolated parts of the forest because they do not require large home ranges (1) (5). Habitat destruction and development in this part of the world does not seem to be slowing down and it is feared that this primate and many others will suffer in due course (2).


Brown howling monkey conservation

Brown howling monkeys benefit from habitat protection in at least 10 different protected areas in Brazil (3). They are also in the 958 hectare sanctuary of Montes Carlos which was first bought by Feliciano Miguel Abdala for a farm in 1944 (7). Abdala was fascinated by the forest’s wildlife and understood that, by trapping humidity, the forest helped to nurture his crops. Abdala therefore conserved large areas of the forest on his property and, encouraged by the World Wildlife Fund (WWF) and scientists, also provided land to build the Caratinga Biological Station in 1983. Since then the reserve has hosted dozens of Brazilian and international researchers, and following Abdala's death in 2000, was established as the Feliciano Miguel Abdala Private Natural Heritage Reserve (7). Conservation International has provided technical and financial assistance, as well as training and equipment, and is now working with local Non Governmental Organisations (NGOs), government officials and private landowners to protect more forest fragments and link them into conservation corridors in this part of the state of Minas Gerais forest zone (7). It is certainly hoped that these positive measures will protect the brown howling monkey and other wildlife of this region for the future (2).

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

For more information on this species see:

Conservation International:



Authenticated (10/12/2005) by Matt Richardson, independent primatologist and writer.



Living in trees.
A species or taxonomic group that is only found in one particular country or geographic area.
Capable of grasping.
Animal with a backbone.


  1. IUCN Red List (January, 2009)
  2. Macdonald, D. (2001) The New Encyclopedia of Mammals. Oxford University Press, Oxford.
  3. Richardson, M. (2005) Pers. comm.
  4. CITES (January, 2004)
  5. Chiarello, A. (1995) Role of Loud Calls in Brown Howlers, Alouatta guariba. American Journal of Primatology, 35: 213 - 222.
  6. Animal diversity (January, 2004)$narrative.html
  7. Conservation International (January, 2004)

Image credit

Brown howling monkey eating fruit  
Brown howling monkey eating fruit

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