Geographic Distribution and Habitat
Black-and-gold howler monkeys, also known as black howler monkeys, are found in the rainforests of central South America. These New World monkeys range through eastern Bolivia, southern Brazil, Paraguay, and northern Argentina. Their habitat varies from tropical semi-deciduous forests to tropical deciduous forests.
Size, Weight, and Lifespan
Black-and-gold howler monkeys are medium-to-large-sized monkeys and are one of the largest primates in South America. Males measure 24–26 inches (60–65 cm) with a 30 inch (76.2 cm) tail. Females measure about 20 inches (50 cm). Males weigh about 15 pounds (6.8 kg) and females weigh in around 10 pounds (4.5 kg).
In the wild, black-and-gold howler monkeys can live to be between 15 and 20 years old. In captivity, they often live to be over 20 years old.
A “U”-shaped bone in the middle of the neck between the chin and thyroid cartilage, known as the foundation of speech.
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Black-and-gold howlers are sexually dimorphic; males are noticeably larger than females, and males and females differ in coloration (sexually dichromatic). Males have black hair, which gives this species their “black” howler monkey name. Females, however, have blonde or golden coloration, giving them the “golden” portion of their name. Infants are born with golden hair, which changes as they mature. Blonde or golden babies are camouflaged in their mothers’ blonde coats.
Black-and-gold howlers have very strong and long prehensile tails that are hairless on the underside. This allows them to grasp, touch, and identify objects, like a fifth hand. Their faces are black and mostly hairless, with bushy eyebrows. Their eyes are brown, medium-sized, and located in the frontal position. They have prominent muzzles and the nostrils lay close together. An enlarged hyoid bone in the neck facilitates their loud howling calls but restricts their arms’ range of motion, so they rely heavily on their prehensile tail for grasping branches while traveling through the trees. The lower jaw is less prominent than that of other howler monkeys, and their neck bulges out further than other howlers.
Chewing mature leaves can be tough (literally); thus, black-and-gold howlers have large upper molars, with sharp shearing crests. The molars are specifically adapted for chewing leaves by shearing and cutting food into small pieces, making food easier to consume.
Black-and-gold howlers are folivores (leaf-eaters) and occasionally frugivores (fruit-eaters). Their diet consists of mostly leaves, but they consume fruits, especially wild figs (Ficus), buds, flowers, and vines. Food sources are located high in the canopy, so black-and-gold howlers rarely come down. In addition, most of their water requirements are met by their food, although they occasionally come down to the ground to drink water in marshes or lakes.
Black-and-gold howler monkeys are one of the only New World primates that regularly consume mature leaves, though young, softer leaves are preferred when they are available. In contrast with their fellow Old World leaf eating monkeys, black-and-gold howler monkeys do not have sacculated stomachs. Their digestive system is comprised of a simple acid stomach and two large sections in the caecum and colon where bacteria is found. The bacteria present in their caecum allows them to digest the high-cellulose content found in their leafy diet. This bacteria is fermented and is used as an energy source.
Behavior and Lifestyle
Black-and-gold howlers are diurnal, which means they are mostly active during the day. They primarily live in the upper and middle strata of the forest canopy; however, they can be found at all levels. At night they retire the upper strata for safety. They travel quadrupedally (on all fours) through the forest at a slow pace to save energy. While feeding, black-and-gold howlers use their tail to suspend from branches.
Each morning, male members of a troop emit an early “chorus” by howling songs to one another. These howls are usually answered by other males. These morning calls occur when troops move into a new feeding site. The howls define and defend the group’s claim on their feeding territory. In this way, one troop is able to identify the location of another troop, so they can avoid that area.
They mark their territories with scent and dung piles on branches of trees. This is done to claim certain branches of trees and also to recognize their group members. However, individuals rarely stray very far from their own territory to find droppings from other group members. Black-and-gold howlers spend about 57 percent of the time resting, due to the low energy returns from their plant diet. Thus, they don’t want to waste their energy on useless travel. In fact, their famous howling helps troops space themselves sufficiently apart from one another. About 76–82 percent of their 0.006–0.01 square-mile (1.7–2.6 ha) territory is defended through vocalizations. The higher the density of food in their territory, the smaller the home-range size. Increased activity levels means increased probability of confrontations with other groups.
Male howler monkeys settle confrontation with howls, grunts, barks, and roars. Females typically spend more of their energy on reproduction than howling, but occasionally chime in to increase volume to scare off predators.
Black-and-gold howler monkeys are the loudest terrestrial animals in the Western Hemisphere.
Howler Monkeys live in social groups with 5 to 19 family members. Group ratios can vary, having more females than males in a group; however, an equal number of males and females in a troop are more common. The largest male in the group is the dominant member.
Daily social interactions include allogrooming and play. Usually a pair of monkeys spend around 15 minutes interacting in an allogrooming session. Howlers play at all age levels—it is the most significant social interaction.
These neotropical primates are one of the loudest terrestrial animals in the Western Hemisphere. Their calls can be heard from up to 3 miles (4.8 km) away. Males awaken each morning with a chorus of calls to other group members. These early morning calls are used to define, defend, and claim their home territory.
Other communication includes tongue-flicking, which is associated with mating.
Black-and-gold howlers are polygynandrous, meaning both males and females have multiple mating partners. Females give birth to one offspring about once a year. They wait about one full year to mate again. Infants are born blonde and remain blonde until 2-1/2 years old. After this point, the males’ fur begins to turn black, while the females’ fur stays blonde.
Females are the primary caregivers for infants and often practice allomothering—sharing the responsibilities of looking after the young. Females raise them until they reach sexual maturity (close to 1-1/2 years old). Once sexual maturity is reached, some males stay with their natal group, while others leave and join a new troop.
Due to their diet, black-and-gold howlers disperse seeds throughout the forest. Oftentimes seeds stick to their fur and will also be dispersed during travel.
The black-and-gold howler monkey is classified as Near Threatened by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN’s Red List of Threatened Species, due to ongoing loss of suitable habitat, hunting pressure, and their susceptibility to disease outbreaks (e.g. yellow fever).
Habitat loss for agricultural developments, cattle farms, and logging for timber and fuel wood influence the the density and group composition of this species. Although howler monkeys are adaptable and flexible in their habitat and diet preference, these threats cause some populations to be small and fragmented. Thus, some populations, such as those in the Argentine provinces of Formosa, Misiones, Salta, and Corrientes, are more threatened than others.
Black-and-gold howler monkeys have been reported to be imported to the United States for laboratory use. In addition, they are also hunted for their meat and fur in some regions.
Black-and-gold howler monkeys are listed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). They also reside in numerous protected areas in Argentina, Bolivia, Brazil, and Paraguay. More monitoring on their population trends should be done in order to understand how habitat degradation affects their group composition. Land, water, and site management is crucial to ensure that this species has an optimal habitat to thrive.
- Bravo SP, Sallenave A., 2003. Foraging Behavior and Activity Patterns of Alouatta caraya in Northern Argentinean Flooded Forest. International Journal of Primatology. 24:825-846.
- Zunino GC., Kolwaleski MM., Oklander LI., Gonzalez V. 2007. Habitat fragmentation and population size of the black and gold howler monkey (Alouatta caraya) in a semideciduous forest in Northern Argentina. American Journal of Primatology 69:1–10.
Written by Tara Covert, June 2019. Conservation status updated July 2020.