Aotus nigricepsblack-headed night monkey

Geographic Range

Aotus nigriceps (black-headed night monkey) is native to neotropical South America. Black-headed night monkeys are found in an area roughly within the boundaries of 5 to 15° south latitude and 75 to 55° west longitude. This area includes the Amazonian and Madeiran forests in Peru, Brazil, and Columbia and several forest areas found in the Huallaga, Ucayali, Yavari, Purus, and Madre de Dios river basins. It encompasses those areas south of the Amazon River to the Madeira River Basin and the northwestern part of the Tapajoz River Basin. Black-headed night monkeys are a species of "red-necked" or "southern" night monkeys. (Aquino and Encarnacion, 1994; Cawthon, 2005; Fernandez-Duque, 2006)


Black-headed night monkeys are usually found in lowland and hillside tropical forest areas. They are usually found in the higher canopy levels of the forest. They choose exclusive sleeping sites in the crooks of branches, especially in trees in the genus Miconia. These trees have large leaves and relatively thick canopy cover. Aotus species generally do not modify their sleeping environments. Other night monkey species, A.vociferans and A. nancymae, have been observed co-occupying sleeping sites with Potos flavus, Bassaricyon gabbi, Coendu bicolor, Tamandua tridactyla, Isothrix bistriatus and bat species. (Aquino and Encarnacion, 1994; Fernandez-Duque, 2005; Khimji, 2005; Wright, 1994a)

  • Range elevation
    0 to 3200 m
    0.00 to 10498.69 ft

Physical Description

Black-headed night monkeys are small primates approximately the same size as a small squirrel. While there are few data concerning the mass of A. nigriceps specifically, Aotus species, both male and female, average 750 g as adults, reaching this size by 14 months of age. Their coats are short and thick. Adult A. nigriceps have dark grey-black agouti pelage on the upper back and forelimbs and orange-tan pelage on the lower back, outer rear legs, and onto the tail. They have three conspicuous black stripes that nearly converge on the forehead. Two of these stripes follow the sides of the face to the maxilla, the central stripe extends to the bridge of the nose. They have white patches over each eye, on the cheeks, and under the mouth. They also have bright orange pelage on the sides of the neck and onto the ventrum, extending from the lower neck, chest and stomach onto the arms, legs and ventral tail. Infants and sub-adults have the same basic coloration. Aotus species have disproportionally large, brown eyes, consistent with their nocturnal habits. They lack a tapetem lucidem. Night monkeys have small external ears that are hidden by their fur. Their digits are long and thin, with straight nails and wide fingertip pads.The second digit of each foot has a curved nail which may be used for grooming. They have an intermembral index of 74, typical of arboreal quadrupeds. The basal metabolic rate is 18 to 24% below that predicted for other 1 kg mammals. (Baer, 1994; Dixson, 1994; Fernandez-Duque, 2005; Ford, 1994; Khimji, 2005; Wright, 1985)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    750 g
    26.43 oz


Black-headed night monkeys are serially monogamous; mates can be displaced due to violence on the part of a same sex interloper. Males and females form bonds that last until one or the other is displaced. Fruitful mating does not occur until a mated pair has been together for one year. Males have small testicles which might be indicative of monogamy and low mate competition. There seems to be no signal that a female is receptive to mating and mating activity takes place both during and outside of the estrus period. Mating encounters are short in length lasting for 1 to 9 coital thrusts. The breeding period in the wild is between August and February, though Aotus species in captivity have been observed to breed year round. (Fernandez-Duque, 2005; Fernandez-Duque, 2006; Ogden, 1994; Wright, 1985; Wright, 1994a; Wright, 1994b)

Neither males or females seem to give reproductive signals and mating activity is independent of female estrus cycles. Reproductive activity in A. nigriceps usually occurs between August and February and the female produces one infant a year. Twins have been observed only rarely, in 1 out of 169 births. Males and females disperse from their natal range as sub-adults between 26 months and 5 years of age, averaging dispersal at 3 years old. The interbirth interval is from 166 to 419 days. The average weight of a newborn is 90 to 150 g. Full weaning occurs at around weeks 18 to 19. Sexual maturity is at 2 years in males and 3 to 4 years in females. (Aquino and Encarnacion, 1994; Dixson, 1994; Fernandez-Duque, 2005; Fernandez-Duque, 2006; Wright, 1985; Wright, 1994a)

  • Breeding interval
    Owl monkeys breed once yearly.
  • Breeding season
    The breeding season occurs between August and February.
  • Range number of offspring
    1 to 2
  • Average gestation period
    4 months
  • Average weaning age
    19 weeks
  • Average time to independence
    18 weeks
  • Range age at sexual or reproductive maturity (female)
    3 to 4 years
  • Range age at sexual or reproductive maturity (male)
    2 (low) years

Black-headed night monkey males are primary caregivers for their young. Females nurse their young every 3 hours but then drive the infant away by biting their feet or tail. Males take over care of the infant, except for nursing, after 2 weeks old. At about 8 weeks old, around the time of weaning, the males begin to drive their young away as well. Young sometimes usurp the territories of their parents after independence. (Dixson, 1994; Fernandez-Duque, 2005; Wright, 1994a)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
  • pre-independence
    • provisioning
      • male
    • protecting
      • male
  • post-independence association with parents
  • inherits maternal/paternal territory


Not much is known about longevity in Aotus nigriceps in the wild. Individuals in captive populations have been observed to live 15 to 20 years. (Fernandez-Duque, 2005; Fernandez-Duque, 2006)

  • Range lifespan
    Status: wild
    11 (high) years
  • Range lifespan
    Status: captivity
    20 (high) years


Black-headed night monkeys are arboreal quadripeds. They are primarily nocturnal, but have been occasionally observed during daylight hours. Black-headed night monkeys live in small family groups, including their young and sub-adult offspring. Aotus nigriceps individuals are highly territorial and defend their range with vocalizations and sexually specific aggression. Males usually attack other males and females usually attack other females. Confrontations last from 5 to 30 minutes and end when one of the groups leaves. Aggression is also the means of mate displacement. A male or female will enter a territory and fight with the resident female or male. If they are successful they will take over the mate and territory of their rival. Interestingly, successful interloper males will also take over the care of any infants of the previous pair. (Aquino and Encarnacion, 1994; Wright, 1985; Aquino and Encarnacion, 1994; Wright, 1985; Aquino and Encarnacion, 1994; Fernandez-Duque, 2005; Wright, 1985; Wright, 1994a)

  • Range territory size
    70,000 to 140,000 m^2
  • Average territory size
    92,000 m^2

Home Range

The home ranges of A. nigriceps are small, averaging 9.2 ha. Nightly path lengths vary from 340 m to 1,025 m (averaging 708 m) depending on the amount of ambient light and prevalent weather conditions. (Fernandez-Duque, 2005; Wright, 1994a)

Communication and Perception

Resonant whoops and low-pitched hoots are the most common forms of vocal communication in Aotus. Whoops are usually used in intragroup encounters at the edges of territories and are used with visual displays and scent marking before aggressive interactions. Hoots are usually used in distance communication by unmated males and females and may be involved in mating rituals. Aotus males and females use both urine and skin secretions in scent marking behavior. (Fernandez-Duque, 2005; Wright, 1985; Wright, 1994a)

Food Habits

Black-headed night monkeys are primarily frugivorous, preferring ripened Ficus fruits. They also opportunistically feed on leaves and flowers as well as moths, beetles, and spiders. However, examinations of fecal matter from A. nigriceps have not yielded significant amounts of leaf fiber or insect matter. This is different from A. vociferans which appears to be more folivorous.

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • fruit
  • flowers


There is little know about predation on Aotus species. Their nocturnality and arboreality helps to protect them from many predators. They rarely leave the trees, only leaving to occasionally cross into other forested areas to forage. (Aquino and Encarnacion, 1994)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Because of their frugivory, black-headed night monkeys are likely to aid in seed dispersal, although little research has been done on their ecosystem roles.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Black-headed night monkeys are important members of native ecosystems.

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no known adverse effects of black-headed night monkeys on humans.

Conservation Status

Currently, black-headed night monkeys are considered a species of lesser concern by the IUCN. Their conservation status could change as continued development in the forested areas in which they live affects their habitat. (Aquino and Encarnacion, 1994; Cawthon, 2005)


Tanya Dewey (editor), Animal Diversity Web.

Adam Davis (author), University of Oregon, Stephen Frost (editor, instructor), University of Oregon.



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

World Map


uses sound to communicate


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


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


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.


an animal that mainly eats fruit


An animal that eats mainly plants or parts of plants.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


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


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.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season


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


Living on the ground.


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


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


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