Family Atelidae
howler and prehensile tailed monkeys

Prehensile tailed monkeys are the largest of the New World Monkeys. There are 24 species in the family Atelidae, including 10 species of howler monkeys (Alouatta), 7 spider monkeys (Ateles), 2 muriquis (Brachyteles), 4 woolly monkeys (Lagothrix), and 1 yellow-tailed woolly monkey (Oreonax). All atelids have prehensile tails that are sensitive and used for grasping objects. (Groves, 2001; Nowak, 1991; Wilson and Reeder, 2005)

Prehensile tailed monkeys are found in Central and South America. The howler monkeys (Alouatta) are the most widespread New World monkey genus, occurring from southern Mexico to northern Argentina. Spider monkeys (Ateles) are also fairly widespread, occurring from southern Mexico through the Amazon basin. Woolly monkeys (Lagothrix) are found only in the Amazon. Muriquis (Brachyteles) are restricted to the southeastern Atlantic rainforest of Brazil and yellow-tailed woolly monkeys (Oreonax) are found only in the cloud forests of a portion of the Peruvian Andes. (Nowak, 1991; Strier, 2004)

All prehensile tailed monkeys are highly arboreal and found exclusively in forests. Some species, such as woolly monkeys (Lagothrix) and some spider monkeys (Ateles) are found only in primary forests but most species also occur in secondary or disturbed forests. (Nowak, 1991; Strier, 2004)

Prehensile tailed monkeys were previously considered part of the large New World monkey family, Cebidae, along with night monkeys (Aotidae) and titi monkeys, sakis, and uakaris (Pitheciidae). Atelidae has recently undergone major taxonomic revision, based both on new molecular research and re-evaluation of museum specimens. Most changes resulted in the recognition of new species but also included the elevation of yellow-tailed woolly monkeys to their own genus, Oreonax, whereas they were previously recognized as a species of Lagothrix. (Groves, 2001; Nowak, 1991; Strier, 2004; Wilson and Reeder, 2005)

Prehensile tailed monkeys are further split into two subfamilies: Alouattinae, the howler monkeys, and Atelinae, including spider monkeys, woolly monkeys, yellow-tailed woolly monkeys, and muriquis. Relationships among the genera of Atelinae remain unresolved. (Groves, 2001; Nowak, 1991; Ryder et al., 2005; Seuanez et al., 1999; Steiper and Ruvolo, 2003; Strier, 2004; Wilson and Reeder, 2005)

Prehensile tailed monkeys are the largest of the New World monkeys. Species range from 382 to 686 mm head and body length in the Atelinae and from 559 to 915 mm head and body length in the howler monkeys (Alouattinae). Atelinae tail length ranges from 508 to 890 mm and weight from 5.5 to 15 kg. Alouattinae tail length ranges from 585 to 915 mm and weight from 4 to 12 kg. Males are substantially larger than females in howler monkeys (Alouatta) and woolly monkeys (Lagothrix), sexes are similar in size in other genera. Dental formula is I 2/2; C1/1; P 3/3; M 3/3. (Nowak, 1991)

Prehensile tailed monkeys are from pale buff or gray (Brachyteles) to dark black (Ateles) in pelage color. Males and females differ in color in some species of howler monkeys. Prehensile tailed monkeys tend to have long limbs, fingers, and tails. This is especially pronounced in spider monkeys and muriquis, where it is associated with brachiation and suspensory locomotion. Woolly monkeys and howler monkeys have more compact bodies and are not as fast and agile as are spider monkeys and muriquis. Female Ateles and Brachyteles have pendulous clitorises. Howler monkeys have a greatly enlarged hyoid bone which is used to help project their very loud roaring vocalizations. They also have an enlarged hindgut. (Nowak, 1991; Strier, 2004)

A captive woolly monkey lived for nearly 25 years, a captive spider monkey lived for 48 years, and a captive howler monkey for more than 23 years. Wild howler monkeys live for over 20 years, with an average of 16 years. (Nowak, 1991)

Prehensile tailed monkeys are diurnal. They spend a large part of every day resting, up to 70% of their time. They are exclusively arboreal, although some species have occasionally been observed descending to the ground to drink, forage, and play. Spider monkeys and muriquis are superb brachiators and exceptionally agile when locomoting in forest canopies. (Strier, 2004)

Prehensile tailed monkeys live in multi-male, multi-female social groups of 3 to 100 individuals. Woolly monkeys often occur in groups of 30 to 40 and spider monkeys in groups of 2 to 30. Howler monkeys often occur in smaller groups of 3 to 19. In ateline genera males are philopatric and females disperse from their natal groups. Both males and females disperse from their natal groups in howler monkeys. Groups don't defend territories, although inter-group conflict can sometimes be intense in howler groups. Home range sizes range from 10 hectares in Alouatta to over 900 hectares in Lagothrix and Brachyteles. (Nowak, 1991; Strier, 2004)

All species use vocalizations to communicate, but howler monkeys are best known for their powerful, long-distance roars. Male howler monkeys roar most often at the boundaries of their home ranges and can be heard by humans up to 2 kilometers away. Some species are also known to apply urine to their hands and feet, depositing scent as they move. (Nowak, 1991; Strier, 2004)

Prehensile tailed monkeys are primarily frugivorous, although they also consume variable quantities of leaves, flowers, nectar, plant gums, new shoots, and insects. Howler monkeys (Alouatta) are the most folivorous of the prehensile tailed monkeys. Diet varies geographically and seasonally, though, with more fruits consumed when available and leaves becoming a more important part of the diet in parts of the year where fruits are less available and in disturbed forests. Prehensile tailed monkeys use their tails extensively. Individuals often feed while suspended, hanging from their tail. (Nowak, 1991; Strier, 2004)

There are few reported predators of prehensile tailed monkeys. They are at risk of predation from arboreal predators, such as large snakes and felids. Large, diurnal raptors may also take these monkeys from forest canopies.

Prehensile tailed monkeys aid in the dispersal of forest trees through their frugivory. (Nowak, 1991; Strier, 2004)

Although large and frugivorous, none of the atelids are considered agricultural pests. (Strier, 2004)

Prehensile tailed monkeys are important in many Central and South American cultures. They are featured in myths and legends and some body parts are thought to have special powers. Their large body size makes many prehensile tailed monkeys a desirable source of meat and the docility of some species makes them popular as pets. Prehensile tailed monkeys are fascinating and ubiquitous components of neotropical forests, making them important for ecotourism. (Nowak, 1991; Strier, 2004)

Both Brachyteles species, Oreonax flavicauda, 3 species of Alouatta, and 2 subspecies of Ateles geoffroyi are on Appendix I of CITES. Alouatta pigra, Ateles marginatus, and Brachyteles arachnoides are considered endangered by the IUCN. Ateles hybridus, Brachyteles hypoxanthus, and Oreonax flavicauda are considered critically endangered. The muriquis (Brachyteles) are the only New World monkeys restricted to the Brazilian Atlantic rainforest, making them especially vulnerable. Brachyteles hypoxanthus populations are estimated at around 500 individuals. Oreonax flavicauda populations, restricted to a small area of the Peruvian Andes, are estimated at 200 individuals. (International Union for the Conservation of Nature, 2007; Nowak, 1991; Strier, 2004)