Aotus trivirgatusnorthern night monkey

Geographic Range

Aotus trivirgatus cover most of tropical South America. From north to south they are found from Panama to northern Argentina. From east to west their range extends from the mouth of the Amazon to its headwaters in Peru and Ecuador. (Macdonald 1997)


Aotus trivirgatus can be found from sea level to 3200 feet elevation, in habitats ranging from rain forests and cloud forests to bordering savanna. They have a narrow range of temperature tolerance between 28 and 30 degrees C. They are arboreal creatures and are generally found traveling from one fruit tree to another throughout the season. Aotus trivirgatus is found to prefer large canopied fruit trees.

(Baer et al. 1994)

Physical Description

Both males and females of Aotus trivirgatus are similar in size with a body length of 24 to 47 cm. Tail length ranges from 22 to 42 cm. Coats range from grizzled brown, gray or reddish backs and off white to orange undersides. Coat color changes from one geographical location to another and for this reason, among others, A. trivirgatus is often separated into many different species or sub-species by different researchers. Aotus trivirgatus is the only nocturnal primate of the neotropics [See comments below]. They have the largest olfactory bulbs and accessory olfactory bulbs of all the New World monkeys presumably due to their reliance on smell during nocturnal activity. They also have large brown/orange eyes. The distinctive markings of the face include a triangular black patch between the eyes and black stripes on the sides, framing their otherwise white face.

(Macdonald 1997, Hershkovitz 1983, Wright 1994) (Hershkovitz, 1983; Macdonald, 1997)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    800 g
    28.19 oz
  • Average basal metabolic rate
    2.499 W


Aotus trivirgatus live in monogamous pairs. There is evidence of long term pair bonding.

Aotus seem to rely most heavily on calls to find mates. Since calls are not common among Aotus trivirgatus, a hoot usually indicates a lone male or female looking for a mate. Copulations generally take place at night, though they have been observed in the day. Females give birth to only one offspring each year and rarely twins. Infants are large and precocial at birth. Gestation length is 133 days. Mating takes place around August and September such that infants are born in the season of high fruit production. (Baer et al. 1994, Macdonald 1997)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
  • Average gestation period
    142 days
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    821 days
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    730 days

Males are the primary caregiver of infants. Care includes carrying, guarding, playing with and sharing food with infants. This demands a significant amount of energy, as the males carry infants up to four months of age and often lag behind the rest of the group. Mothers nurse their young every 2 to 3 hours. Infants are large in comparison to their parents' body mass and grow quickly. Infant size and growth might explain the evolutionary adaptation of monogamy and male parental care, since infants demand more care than a single mother can provide.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
    • protecting
      • male
  • extended period of juvenile learning



Aotus trivirgatus are usually found in family groups where older siblings live with their parents well past infancy and help the mating pair to raise their younger offspring. It has been suggested that this too is a result of the high energy demands of infants. Also, there are limited opportunities for juveniles and subadults to encounter single owl monkeys of the opposite sex with whom to break off from their natal group and form a new pair.

Playing behavior in A. trivirgatus has been observed primarily between infants, juveniles, subadults and fathers. This generally occurs in the months that fruit is most abundant.

Aotus trivirgatus are territorial animals with a territory range of about 9 hectares. They defend these territories, and aggression will result when neighboring groups encounter each other at the borders of territories. Aggressive behaviors include loud whoop-like vocalizations, stiff legged jumping, chases and sometimes wrestling matches. Males and females participate in these territorial battles or standoffs. Conflicts rarely last more than 10 minutes and one group usually retreats.

(Wright 1994, Macdonald 1997)

Communication and Perception

Food Habits

Aotus trivirgatus eat primarily fruits, insects, nectar and leaves. They will also complement their diet with lizards, frogs and eggs for protein. During times when food is scarce, they seek out mostly nectar, figs and insects. At this time of year they seem to have the advantage over similar sized diurnal species that were chased away from these food sources by larger diurnal monkey.

(Baer et al. 1994)

  • Animal Foods
  • amphibians
  • reptiles
  • eggs
  • insects
  • Plant Foods
  • leaves
  • fruit
  • nectar

Economic Importance for Humans: Positive

Aotus trivirgatus have been used as a food source by many indigenous peoples of the neotropics. More recently they have proved invaluable as laboratory animals and have been used for various studies and experiments in testing human diseases and potential treatments. One example is the role that A. trivirgatus have had in testing antimalarial drugs, since they too can be carriers of the human malaria parasites. Commercially there is also a market for owl monkeys as pets. (Baer et al. 1994, Geiman and Meagher 1967)

Conservation Status

Aotus trivirgatus are being threaten by extensive deforestation of the tropical rainforests of South America. They are sensitive to clear cutting as well as selective deforestation, because this limits the diversity of diets within each group's limited territory. Owl monkeys are also hunted for their meat, skins, skulls, and teeth. They are hunted primarily by subsistence hunters who have been forced to turn to these smaller monkeys for food because larger game is no longer available. Trade to the U.S. and other countries as lab animals and pets also diminished the populations in the 70's. Today government bans in most South American counties and the U.S. limit export and import, thus reducing the impact of trapping as a threat. Protected areas in many South American countries have also helped in the conservation of this species. Unfortunately, due to economic and political problems, bans on hunting, trapping and deforestation in many of these areas are not enforced. (Baer et al. 1994)

Other Comments

Aotus trivirgatus differ from most nocturnal animals by having color vision. This fact, along with the structure of the eye, suggests that the ancestors of the night monkeys were diurnal. Though they have evolved very large eyes for low light conditions their activity is dependent on moonlight and their activity is limited on very dark nights. (Macdonald, 1997)


Alicia LaValle (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.



living in the southern part of the New World. In other words, Central and South America.

World Map


Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


Having one mate at a time.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


an animal that mainly eats all kinds of things, including plants and animals


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement


Baer, J., I. Kakoma, R. Weller. 1994. Aotus: the Owl Monkey. San Diego, CA: Academic Press.

Geiman, Q., M. Meagher. 1967. Susceptibility of New World monkeys to Plasmodium falciparum from man. Nature, 215: 437-439.

Hershkovitz, P. 1983. Two new species of night monkeys, genus Aotus (Cebidae, Platyrrhihi) A preliminary report of Aotus taxonomy. American Journal of Primatology, 4: 209-243.

Macdonald, D. 1997. Encyclopedia of Mammals. NY: Facts on File Inc..