BROWN WOOLLY MONKEY
Geographic Distribution and Habitat
Occupying the lush forests of the Amazon lowlands in Brazil, Peru, Colombia, Ecuador, and possibly parts of Venezuela, the brown woolly monkey (Lagothrix lagothricha), also called the common woolly monkey or Humboldt’s woolly monkey, is a large, charismatic New World primate. They live out their lives in primary terra firma rainforest, although sometimes they may be able to live in disturbed forests, and they occasionally wander into flooded forests to feed.
Woolly monkeys are, along with spider monkeys and muriquis, part of the subfamily Atelinae. This group is collectively known as the atelines and all share a defining evolutionary characteristic: their long prehensile tails. The taxonomy of the woolly monkey genus (Lagothrix) has long been a subject of debate, with regular revisions to the classifications being published and discussed. As of January 2021, the International Union for the Conservation of Nature (IUCN) currently holds that there are two species within Lagothrix: the Peruvian yellow-tailed woolly monkey (L. flavicauda), and the brown woolly monkey. Other woolly monkey classifications, such as silvery, gray, and Colombian woolly monkeys, are considered by the IUCN as subspecies of the brown woolly monkey. Naturally, these classifications in no way change anything about the biology of these animals, only how they are referred to by people.
Size, Weight, and Lifespan
Brown woolly monkeys are one of the largest New World primates by weight. Females weigh an average of 13 lbs (5.75 kg) and males weigh an average of 20 lbs (9.0 kg). They range in head and body length from 16 to 24 inches (40–60 cm), with the tail adding another 24 to 28 inches (60–72 cm). They live to approximately the age of 30.
The secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young.
The tail of an animal that has adapted to be able to grasp or hold objects.
Visit the Glossary for more definitions
As their name suggests, brown woolly monkeys have short, thick hair covering almost their entire bodies save their faces, hands, and feet, which are black. Their hair can be brown, tan, gray, olive, reddish, or black, and these color variations tend to correlate somewhat with geography. For example, gray and black individuals are more common at the base of the Andes in Colombia, while olive-colored individuals are most often found in Brazil. On some individuals, the hair is darker on their heads and limbs, while in others the hair is a uniform color throughout. Newborns are born tan.
Their close relation to spider monkeys is seen in their very long arms, legs, and prehensile tail, adaptations that make it possible for them to glide effortlessly through thick forest. Males are larger than females and have longer canine teeth.
Brown woolly monkeys are primarily frugivores (they prefer fruit), supplementing their diet with leaves, seeds, and small invertebrates. They tend to prefer ripe fruit, and often eat seeds instead when ripe fruit is not available. In July in Amazonian Brazil, insects make up a particularly large and important part of their diet.
Behavior and Lifestyle
Brown woolly monkeys are arboreal and diurnal (active during the day), spending nearly all their lives in the trees, usually at a height of about 38 feet (12 m) above the forest floor. While they typically move at a slow, relaxed pace, if pressed they can reach a top speed of 35 mph (56 km/hr). They usually move about quadrupedally (on all fours), although they use their long arms, legs, and tails for brachiation. Also called arm swinging, brachiation is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms. On the rare occasions they find themselves on the ground, they can stand bipedally using their tail for support. Brown woolly monkeys typically travel about 3,200 feet (1 km) per day.
The Portuguese name for woolly monkeys is “barrigudo,” meaning “pot-bellied.”
Brown woolly monkeys live in multi-male multi-female social groups containing anywhere from ten to 70 members. Groups follow a fission-fusion dynamic in which group composure tends to be fluid and not strictly defined. Larger groups are often composed of multiple family units that may feed or travel separately from each other during the day, coming together again to sleep. Some individuals, usually subadult females, may leave their own group temporarily, spending between a few hours to a few days with a different group before returning. Home ranges vary from 1.5 to 4 square miles (4–11 square km), and often overlap with other groups’ ranges. A peaceful species, brown woolly monkeys are not territorial, and even during times of food scarcity, they regularly interact and share space with neighboring groups. However, when mating opportunities are scarce, groups tend to keep to themselves more.
Brown woolly monkeys can communicate to each other in a large variety of ways. One important method is through facial expressions, which they can use to communicate subtle changes in mood or intention. Their vocalizations are loud, and include sounds described as “barks” and “screams.” Brown woolly monkeys also use chest rubbing, a method of scent marking. This is often used by dominant males when moving into new territory.
Males display antagonism towards each other by shaking branches, defecating, and barking. Affection is shown between group members by allogrooming, with adult males receiving the most grooming. Adult females are usually groomed by their daughters. Juveniles in a group bond with each other through play, which they often engage in around midday.
Female brown woolly monkeys have a receptive period in their estrous cycle that lasts 3 to 4 days, occurring roughly once per month. Females indicate their readiness to mate through social cues. Conception most often occurs between September and January, when ripe fruit tends to be abundant. Births are concentrated between May and September, when ripe fruit is scarce. This allows female brown woolly monkeys to accumulate energy reserves throughout their pregnancy from the abundant sources of food, so that they are well-fed throughout gestation and have plenty of energy stored to use for lactation.
After a seven-and-a-half-month gestation, brown woolly monkeys give birth to a single offspring, which is carried ventrally by the mother for the first month of life. After about six weeks, the baby more frequently climbs to their mother’s back. They begin to become independent after about two months of age, although they are nursed until they are about a year old. Female brown woolly monkeys typically reach sexual maturity at about 6–8 years of age, while males mature at about five years of age. Females typically give birth every other year. Their generation length is about 15 years.
Woolly monkeys live sympatrically with capuchins, howler monkeys, spider monkeys, and other primate species of the Amazon lowlands. Their predators include birds of prey and large carnivores, such as jaguars. Their mostly frugivorous diet makes them important seed dispersers.
The International Union for Conservation of Nature lists the brown woolly monkey as Vulnerable (IUCN, 2020), appearing the IUCN’s Red List of Threatened Species. This designation is based on a predicted population loss of 30% or more between 2018–2063, a time period comprising three generations. This prediction is based on data showing forest loss trends throughout the species’ habitat, and the fact that brown woolly monkeys are often hunted for meat.
Like most threatened species, the major threat against brown woolly monkeys is habitat loss. Over the last 50 years, an astounding 17% of the Amazon rainforest has been destroyed, most of it to clear space for cattle ranching. This is a staggering loss to global biodiversity, considering that the Amazon is the most biodiverse place on earth. This loss directly impacts millions of species, including woolly monkeys. Unfortunately, this loss is only expected to continue in the coming decades. Forest cover data from the Global Forest Watch shows a predicted 10–15% loss of forest habitat in parts of Brazil, Peru, Colombia, and Ecuador over the next 45 years.
Another threat against brown woolly monkeys is hunting pressure. They are one of the most intensely hunted primates in South America. They are primarily hunted for their meat, but they are also collected for their skins and for taxidermy displays. Unfortunately, woolly monkeys are not uncommon in the pet trade. To collect infants, the mother must first be killed. It has been estimated that for every live brown woolly monkey that reaches the pet trade market, at least 10 adult females have been killed.
Brown woolly monkeys are protected by several protected habitats, such as Juami-Japurá Ecological Station in Brazil, Serrania de Chiribiquete National Natural Park in Colombia, and Cayambe-Coca Ecological Reserve in Ecuador. They are also protected under Appendix II of the Convention on International Trade in Endangered Species (CITES).
- Deane, A.S., Organ, J., Evie, V., Muchlinski, M. and Butterfield, T. 2020. The comparative and functional anatomy of appendicular musculature of Humboldt’s woolly monkey (Lagothrix lagotricha): What can a (mediocre) suspensory monkey tell us about and human locomotor evolution?. The FASEB Journal, 34: 1-1. https://doi.org/10.1096/fasebj.2020.34.s1.05709
- Ellis, K.M., Abondano, L.A., Montes‐Rojas, A., Link, A., Di Fiore, A. 2021. Reproductive seasonality in two sympatric primates (Ateles belzebuth and Lagothrix lagotricha poeppigii) from Amazonian Ecuador. Am J Primatol; 83:e23220. https://doi.org/10.1002/ajp.23220
- Ellis K., Di Fiore A. 2019. Variation in Space Use and Social Cohesion Within and Between Four Groups of Woolly Monkeys (Lagothrix lagotricha poeppigii) in Relation to Fruit Availability and Mating Opportunities at the Tiputini Biodiversity Station, Ecuador. In: Reyna-Hurtado R., Chapman C. (eds) Movement Ecology of Neotropical Forest Mammals. Springer, Cham. https://doi.org/10.1007/978-3-030-03463-4_10
Written by K. Clare Quinlan, January 2021