Aotus lemurinus

Geographic Distribution and Habitat

The Colombian night monkey is a New World monkey with a host of aliases—including gray-bellied night monkey, gray-bellied owl monkey, lemurine night monkey, and lemurine owl monkey—and is native to the South American countries of Colombia, Venezuela, and Ecuador.

Primary and secondary evergreen tropical rainforests, where the trees are evenly dispersed, are Colombian night monkeys’ preferred habitat. Although they can be found at all levels of the forest canopy, they are most commonly found in dense vine tangles at 3,300 to 10,500 ft (1,000 to 3,200 m) above sea level. Rarely are Colombian night monkeys found on the ground. Montane and dry scrub forests provide alternative residences to the species.

Colombian night monkey range, IUCN 2008

Size, Weight, and Lifespan

At 2 lb (920 g), males carry a little more girth than female Colombian night monkeys, who barely tip the scales at 1 lb 15 oz (875 g). Other than this small weight difference, no other sexual dimorphism, distinct differences in  appearance, exists between the sexes.

The longest recorded lifespan for a captive Colombian night monkey is 33.8 years.


Enormous, closely-set brown eyes, which appear to be outlined with thick, black eyeliner, reflect a bright reddish-orange eye shine and are accented by thick, bushy white “eyebrows”— contributing to this primate’s “owlish” nickname, or alias. A three-pronged furry black marking, almost in the shape of a pitch fork, extends from the crown of the Colombian night monkey’s head, with the widest prong, or stripe, finding a place between the monkey’s wide eyes before stretching to an unobtrusive dark muzzle. Each of the other prongs frames either side of the monkey’s face. Tiny ears peek out from either side of the small, rounded, furry, gray head.

A dense fur coat cloaks the Colombian night monkey’s body and ranges in color from gray with yellow highlights on the monkey’s back, to pale orange on the belly. The monkey’s long, nonprehensile tail, which is incapable of grasping or gripping objects, is mostly black but may have brown or dark orange coloring; the tip of the tail is always black.

Fitted with longer legs than arms, the slender-limbed Colombian night monkey is able to easily leap from tree to tree. The fingers of this owl-faced primate are long and delicate (think of “piano fingers!”) with wide pads on the finger tips. A special grooming claw occupies the fourth digit of each foot.


Colombian night monkeys are a mostly frugivorous species, which is a fancy way of saying that they eat a lot of fruit. Small, ripe fruits with a garnish of nectar and leaves is their meal of choice. However, when fruit is scarce, insects—and even birds—are on the menu.

Behavior and Lifestyle

Nighttime is for foraging, when Colombian night monkeys move deftly through the forest canopy on all fours (quadrupedally) or by leaping—up to 10 to 16 ft (3 to 5 m). They travel the same route each night; scientists believe that night monkeys memorize foraging routes during their moonlit travels.

Two advantages of nighttime foraging are the presence of nocturnal insects (monkey snacks!) and the absence of diurnal primate species who enjoy the same fruit as Colombian night monkeys but whose nature keeps them in bed at night. Besides decreased competition from daytime foragers, the monkeys are able to avoid daytime predators, including wild cats, snakes, and birds of prey.

Daylight hours are spent sleeping in dense brush, vines, or inside tree hollows.

Fun Facts

The Colombian night monkey belongs to the Aotus genus, the only truly nocturnal monkeys in the world.

Daily Life and Group Dynamics 

Small family groups of about five individuals, comprised of a monogamous breeding pair and their offspring, are the norm for Colombian night monkeys. Nocturnal by nature, Colombian night monkeys are most active several hours after dusk and before dawn, and during periods of bright moonlight.

Except for foraging, Colombian night monkeys are mostly sedentary. Social grooming, common in many primate species, is not the norm for Colombian night monkeys. This behavior is reserved for a mating male and female prior to copulation; it’s also present among parents who groom their newborns.

This species is territorial, however. Using brown, oily secretions from the base of their tail, the monkeys will mark the boundaries of their territory and defend this area of approximately 12 to 44.5 acres (5 to 18 hectares) from intruders.


Colombian night monkeys communicate through a vast repertoire of vocalizations, olfactory behavior, visual cues, and tactile actions.

Vocalizations include soft, low-pitched “whoops” (a “resonant whoop” is a series of grunts that build in intensity to communicate an individual’s claim of a fruit tree; may also be emitted as a threat display during hostile encounters); guttural rumblings, grunts, clicks, owl-like hoots (a long, low hoot call communicates sexual advertisement, used by females or younger males when looking for mates; may also be used by a juvenile who has been separated from his group); squeaks, moans, and high-pitched screams.

Olfactory behavior includes urine washing, performed by an individual when he wishes to convey sexual attraction. After urinating on his hands, a male will rub his hands on a tree branch or other surface, leaving an olfactory “love note” to the female whom he hopes to lure.

To demarcate their territory, Colombian night monkeys will mark the boundaries with brown, oily secretions from the base of their tail.

Besides being a prelude to copulation, individuals perform social sniffing as a kind of greeting or a method to perhaps gain information about one another—not too unlike the way dogs greet one another. The most commonly sniffed body areas are the armpits and genital region.

Visual cues are postures that convey specific information. An arched back conveys aggression; swaying back and forth with hands free and palms facing outward precedes a calculated escape from a predator; rubbing one’s genital region against a tree or other surface is performed by both sexes, usually in the context of hostile encounters or during pre-copulation. Females engage in this behavior more often than males, leading scientists to believe that rubbing may be a submissive display; in an instance where a female was dominant over a male, scientists observed that the male engaged in rubbing, upon encountering the female.

Tactile communication includes a mother Colombian monkey’s rejection bite, which she administers to her infant in a most non-maternal rebuke.

Parents use their mouths to groom the face and genitals of their newborns. Other than this parental predisposition, social grooming occurs only between a pair of adults engaged in copulation.

Reproduction and Family

Colombian night monkeys reach sexual maturity at about 2.5 years of age. When it comes to mating, males are typically the initiators. After quietly approaching his selected female, a male will sniff her body—a practice known as social sniffing. If she feels like it, a female might reciprocate and social sniff her male suitor. This brief foreplay is followed by an even shorter (and perfunctory) act of copulation.

After a gestation period of about 4.5 months, a female Colombian night monkey gives birth to a single offspring; on occasion, she might give birth to twins. The minimum interbirth interval is 5 months.

The species’ monogamy informs its co-parenting style. During an infant’s first week of life, she is carried between her mother’s hip and thigh. From week two on, however, the father carries his offspring, first between his hip and thigh and then on his back when the infant is a little older. During this time of paternal care, the infant returns to her mother only to nurse. At the end of a nursing session, the mother will reject her baby. Should her baby attempt to remain at her bosom, the mother will bite her baby’s tail, hands, or feet, causing her baby to squeal.

By 18 weeks old, an infant is able to move independently. She returns to her father only in the event of a disturbance, for protection. Both males and females leave their birth group when they are between 2.5 and 3.5 years old.

Ecological Role

Colombian night monkeys help to naturally replenish their habitat by dispersing seeds of the fruits they eat through their feces.

Conservation Status and Threats

The Colombian night monkey is listed as Vulnerable (IUCN, 2020) by the International Union for Conservation of Nature, appearing on the IUCN Red List of Threatened Species.

Much of the habitat of this night monkey is impacted by human disturbances, including deforestation, expanding illicit crops, coffee and armed conflict. Colombian night monkeys have also been traditionally hunted and eaten by local communities, and they have been sold through the illegal pet trade.

However, another threat—perhaps the most insidious—comes from the biomedical and pharmaceutical industries. Agents for these industries kidnap the monkeys from their wild, forested habitats and have them transported to medical research labs where the monkeys become unwitting “models” for medical research. Because Colombian night monkeys are susceptible to malaria, scientists inject their immobilized subjects with anti-malaria compounds and vaccines to measure the effects.

During 2007-2008, 4,000 night monkeys were traded, generating a value of over $100,000 (U.S.). However, indigenous collectors—agents of the pharmaceutical industry charged with kidnapping these monkeys— received less than 10 percent of these revenues (according to the Whitley Fund for Nature, a UK-based charitable organization dedicated to encouraging and supporting nature conservationists). 

Conservation Efforts

The Colombian night monkey is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce.

In addition, this species occurs within protected areas: the Cofán Bermejo Ecological Reserve, Llanganates National Park and Sumaco Napo Galeras National Park in Ecuador, and Tama National Natural Park and Puracé Natural National Park in Colombia, which may help protect populations in these areas from the threat of deforestation.

New England Primate Conservancy, the New England Anti-Vivisection Society, the National Anti-Vivisection Society, and Animal Defenders International (ADI) are among those organizations advocating to keep primates out of research labs, proposing instead scientific methods that are humane and superior to experimenting upon nonhuman primates.

ADI celebrated a 2012 ruling by Colombia’s Administrative Tribunal of Cundinamarca to revoke permits to capture wild night monkeys for malaria experiments, calling the decision a “breakthrough for animal protection and conservation.” The Tribunal ruled that research on these night monkeys breached Colombia’s commitment to CITES. Had the permits not been revoked, 4,000 of these primates would have been trapped and sent to research labs for experiments related to malaria vaccine at the Institute of Immunology Foundation of Colombia (FIDIC).


Written by Kathleen Downey, September 2017