MANTLED HOWLER

Alouatta palliata

Geographic Distribution and Habitat
Mantled howler monkeys, also called Ecuadorian mantled howling monkeys and South Pacific blackish howling monkeys, are found on the southern tip of Mexico and in Veracruz, southern Guatemala, Costa Rica, Panama, the west coast of Ecuador, and Colombia at elevations of up to 6,562 feet (2 km).

Mantled howlers live in lowland rain forests, gallery forests, cloud forests, dry forests, and mangroves, and are found in both primary and secondary forests. They use all levels of the canopy, but prefer the upper canopy region, where there is a mix of vegetation, branches, vines, and trees of varying sizes. Food is plentiful at this level of the rainforest and many animals—including howler monkeys—find shelter from predators, as well as strong winds and rain from tropical storms.

Mantled howler monkeys are among the most commonly heard—that is to say loudest—primates in many Central American national parks including Manuel Antonio, Corcovado National Park, Santa Rosa National Park, and the Monteverde Cloud Forest Reserve.

Mantled howler monkey geographic range. Map: IUCN, 2020

Size, Weight, and Lifespan
Howler monkeys are among the largest of all New World primates. Males weigh between 10 and 20 lbs (4.5-9 kg) and can be as large as 30 lb (13.6 kg). Females weigh between 8 and 16 lb (3.5-7.3 kg). The average body length for males is between 20 and 27 inches (51-68.6 cm); females are usually 18 to 25 inches (45.7-63.5 cm) long. At 21-26 in (53.4-66 cm) long, mantled howler tails are longer than their head-to-body length.

Mantled howlers can live 15-20 years in the wild.

Appearance
Fairly stocky monkeys, mantled howlers are covered in black hair, except for two golden patches on their flanks. They are called mantled howlers because of the long golden hairs on their sides. Their tails are prehensile with a naked patch on the underside toward the tip, which is used for grasping onto branches. Their faces are mostly bare with growth that resembles a beard. These beards are typically longer in males than females.

Infants are golden brown to silver in color. They increasingly transition to adult coloration until they reach about 12 weeks old, when they resemble their adult counterparts.

Mantled howler monkeys are sexually dimorphic, which means there are differences between males and females in size, behavior, and other characteristics. Males are slightly larger than females and exhibit differences in skeletal structures. Male mantled howler monkeys have a large hyoid bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. The hyoid enables them to produce the loud sounds from which they receive their apt name: howlers. The upper molars of howler monkeys have very sharp shearing crests that are used for grinding leaves.

Photo credit: Hans Hillewaert/Creative Commons

What Does It Mean?

Cloud forest:
A forest that contains a persistent or seasonal presence of low-level clouds and mist. 

Diurnal:
Active during daylight hours.

Dominance hierarchy:
A type of social hierarchy that arises when members of a social group interact, often aggressively, to create a ranking system. In social groups, member are likely to compete for access to limited resources and mating opportunities. 

Estrus:
A recurring period of sexual receptivity and fertility in many female mammals.

Gallery forest: 
A forest that serves as a corridor along rivers or wetlands and projects into landscapes that are otherwise sparsely treed, such as savannas, grasslands, or deserts.

Mangrove: 
A mangrove refers to two different things: a tidal swamp ecosystem found in tropical deltas, estuaries, lagoons, or islands; and the characteristic tree species populating this ecosystem. Mangrove trees have developed unique adaptations to the harsh conditions of coastal environments.

Prehensile Tail:
The tail of an animal that has adapted to be able to grasp or hold objects.

Quadrupedal:
Using four limbs to move about. This word comes from the Latin meaning “four feet.”

Tannins:
A bitter tasting organic substance commonly found in plant tissues. 
Also referred to as “tannic acid.”

Visit the Glossary for more definitions

Diet
Mantled howler monkeys spend most of their time munching on leaves, fruits, and flowers, though food habits vary seasonally with resource availability.

Flowers are abundant during the dry season; fruits are available during the wet season. Mantled howler monkeys are very selective about the species on which they feed. Their food choices are based on digestibility, nutrient value, and tannins (which can be quite unpleasant for howlers). Tannins are found in plant tissues and consist of high levels of acid, which can cause stomach irritation. Mantled howler monkeys are equipped with large salivary glands that break down tannins before they reach the stomach, enabling them to consume leaves that other species cannot. Grazing on these leaves gives mantled howler monkeys access to a niche that is rarely exploited by other mammals. However, they prefer to eat young leaves with a higher protein-to-fiber ratio and a lower tannin content.

While foraging, they spend an equal amount of time feeding on both leaves and fruits. In Los Tuxtlas, Mexico, however, a species known as Atta cephalotes, a leaf-cutting ant, inflicts significant pressure on available leaf resources, which causes competition between arboreal mammals like the mantled howler.

Behavior and Lifestyle
Mantled howler monkeys are arboreal and diurnal; that is, they live in trees and are most active during the day. They move through the forest canopy by walking and climbing quadrupedally or suspending themselves below the branches. They hang by their arms and support themselves with their long prehensile tails while feeding. At night they sleep on horizontal branches.

There is slight variation in locomotion style between males and females. Males climb less, leap more, and prefer the higher canopy, compared to females. When necessary, both males and females will cross open areas between forest patches on the ground and even swim short distances.

This species is polygynous, meaning one male mates with multiple females. Mantled howler monkeys do not have a particular breeding season and instead tend to breed at any time of the year. Many births occur in late December and January.

Fun Facts

Mantled howler monkeys have a prehensile tail that acts as a “fifth limb.” They are able to grasp on to branches and hang hands-free. 

Daily Life and Group Dynamics 
Mantled howler monkeys are highly sociable creatures. Dominance hierarchies within their groups demonstrate complex social interactions that may be the opposite of what one might expect. For example, among mantled howlers: young adults have a higher ranking; middle-aged adults are intermediately ranked; and older adults have a low ranking. In many species, rank is achieved over time and experience.

Group sizes range from 10 to 20 individuals, usually with 1 to 5 adult males and 5 to 10 adult females and their offspring. Males form bachelor groups and may challenge dominant males in an effort to usurp their troops.

Females form stable social units and rarely leave their natal group. The gender ratio is close to four females for every male. If the ratio of females drops below four, older males may behave aggressively toward younger males in an effort to drive them off, or they will wander off themselves to find a new troop. Thus, immigration plays an important role in population size and dynamics.

Communication
One of the most common forms of communication between mantled howler monkeys is vocal communication. The loudest New World monkey species, their calls can be heard up to 3 miles (5 km) away.

A long call, amplified by the hyoid bone, can travel large distances. These calls communicate group location, distance, and composition. They can also be directed toward solitary individuals and other members of the group. Long calls are often heard at dawn.

Neighboring groups communicate through vocal calls between the males. They emit woofing, grunting, barking, and howling sounds.

Olfactory communication has been reported in male mantled howler monkeys. Males have been observed tasting the urine of females, possibly to check for estrus status.

Tactile communication is mainly demonstrated by females via grooming.

Reproduction and Family
After six months of gestation, the mother gives birth to one offspring. The newborn is licked clean and carried by her or his mother. During the first few weeks after birth, the mother nurses the infant. After 3 weeks, the infant begins to eat leaves. As the infant matures, he or she begins to ride on the mother’s back. When traveling on the mother’s back, the infant grasps the base of the mother’s tail with his or her own. The child is constantly with the mother for the first four months. During this time, mother and infant do not venture more than 6.5 ft (2 m) away from each other. Occasionally, females other than the mother may care for the child. At about 10-11 weeks, the baby starts to forage independently and spends much more time on his or her own. Males reach maturity at about 42 months and females at about 36 months.

Ecological Role
Mantled howler monkeys disperse seeds from the plants they eat throughout the forest, which is highly beneficial to the ecosystem. Their feces are used by dung beetles, which helps recycle nutrients into the soil.

Conservation Status and Threats
The International Union for Conservation of Nature Red List of Threatened Species lists the mantled howler monkey as Vulnerable (IUCN, 2015), appearing on the IUCN’s Red List of Threatened Species due to habitat loss and fragmentation as a consequence of economic activities, as well as hunting for the pet trade.

Aa population reduction of 30% or more is inferred over the course of 30 years or three generations. This is based upon Global Forest Watch data for southeastern Mexico south through Central America, into western Colombia and Ecuador, and extreme northern Peru. The data suggest that, should forest loss continue at the same rate that has impacted the previous generation (2003-2018), 19% of this species’ suitable habitat is likely to be lost by the year 2048. Combined with continued evidence of hunting, both for the pet trade and for bushmeat, these threats put the mantled howler above the threshold for Vulnerable status.

Residential and urban development, agriculture, and aquaculture have led to large areas of habitat destruction. Forests have been largely fragmented and destroyed for housing and urban areas. Annual and perennial non-timber crops and livestock farming and ranching in areas of Panama have also fragmented their forests. In Colombia, howler monkeys are at risk from hunting; their habitats are also at risk here for pasture and agricultural use. Over 90% of forest on the Atlantic coast of Colombia has been destroyed for these purposes. Ecosystem conversion and ecosystem degradation are ongoing threats to not only the mantled howler monkey, but to other species that share the same habitats.

Conservation Efforts
Mantled howlers are found in many protected areas throughout Mexico, Central America, and South America. They are also listed on Appendix I of the Convention on International Trade in Endangered Species (CITES). In addition, there are educational programs that bring awareness to this species and show how to take conservation action. There are also controls over international trade and management for these monkeys.

References:

  • https://animaldiversity.org/accounts/Alouatta_palliata/
  • http://www.bioone.org/doi/full/10.1896/044.016.0101
  • http://animalia.bio/mantled-howler-monkey
  • https://www.iucnredlist.org/species/39960/10280447
  • http://www.theprimata.com/alouatta_palliata/
  • https://tropical-rainforest-facts.com/Tropical-Rainforest-Layer-Facts/Tropical-Rainforest-Canopy-Layer-Facts.shtml
  • ​​Kinzey, W.G. 1997. Alouatta. in New World Primates: Ecology, Evolution, and Behavior. ed. Warren G. Kinzey, Aldine de Gruyter, New York.
  • Jones, C.B. 1980. The Functions of status in the mantled holwer monkey, Alouatta palliataGRAY:Intraspecific competition for group membership in a folivorous neotropical primate, Primates. 

Written by Tara Covert, November 2018. Conservation status updated July 2020.