Aotus nancymaaeMa's night monkey

Geographic Range

Aotus nancymaae (Ma’s night monkey) can be found in the north central Amazonian neotropics of northern Peru and western Brazil in South America. This species was once thought to belong to the species Aotus trivirgatus, whose range was believed to reach from southern Central America to South America. (Aquino and Encarnacion, 1986a; Aquino and Encarnacion, 1986b; Bales, 1980; Eisenberg and Redford, 1999; Emmons, 1990; Moynihan, 1996)


Although considered habitat generalists (Greenberg, 1999), A. nancymaae are found primarily in lowland tropical rainforests. Aotus nancymaae prefer seasonally flooded forest regions because softer trees provide hollows and hanging shrubbery in which they hide and nest (Aquino and Encarnacion, 1986a, Greenberg, 1999). At night, while active, they occupy the upper levels of the canopy while foraging on fruits and flowers. During the day, they reside within the lower canopy of the forest, remaining inactive. Strongly arboreal, A. nancymaae do not naturally move on the ground. It has only been when individuals were in emergency situations that terrestrial locomotion has been documented (Aquino and Encarnacion, 1986a, Moynihan, 1976). (Aquino and Encarnacion, 1986a; Eisenberg and Redford, 1999; Emmons, 1990; Greenberg, 1999; Moynihan, 1996)

Physical Description

Aotus nancymaae are small monkeys with non prehensile tails. Their pelage is light grey to light brown. Belonging to the “red necked” subdivision of Aotus, these monkeys have reddish orange hair along the sides of the neck and the inner lining of the limbs and tail base (Eisenberg and Redford, 1999, Emmons, 1990). The tail has a black tip and hangs straight down, a distinctive characteristic of all Aotus species (Emmons, 1990). The fur is short, dense and soft (Moynihan, 1996). Aotus nancymaae have characteristically large eyes. Their hands are well developed for grasping, capable of more independent movement than other New World primates (Moynihan, 1976). A post caudal gland is present and enlarged in both sexes; this is used for marking territory. The genitalia of adult A. nancymaae are brightly colored and displayed (Aquino and Encarnacion 1986b). (Aquino and Encarnacion, 1986b; Eisenberg and Redford, 1999; Emmons, 1990; Greenberg, 1999; Moynihan, 1996)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    550 to 950 g
    19.38 to 33.48 oz
  • Average mass
    788 g
    27.77 oz
  • Range length
    530 to 774 mm
    20.87 to 30.47 in
  • Average length
    637 mm
    25.08 in


Aotus nancymaae live in small groups, consisting of a monogamous breeding pair and up to the three of their most recent offspring. When they reach adulthood, an individual is forced from its family group and wanders about seeking a mate (Aquino and Encarnacion, 1986b). To attract a mate, A. nancymaae individuals emit squeaks while traveling through occupied territories (Aquino and Encarnacion, 1986b, Greenberg, 1999, Moynihan, 1976). Females have an estrus cycle of about 19 days (Greenberg, 1999). Females give birth to one young or rarely two young at a time (Aquino and Encarnacion, 1986b, Greenberg, 1999); two young may be the result of a high availability of resources. Breeding pairs continue to mate throughout life. (Aquino and Encarnacion, 1986b; Greenberg, 1999; Moynihan, 1996)

Aotus nancymaae mate year round, but it is speculated that offspring are conceived dependent of the availability of resources. This results in seasonal breeding in the wild (Greenberg, 1999). The breeding pair is able to care for up to three offspring at a time. There are no accounts of infanticide (Aquino and Encarcion, 1986b, Bales, 1980, Greenberg, 1999). Aotus nancymaae give birth to young that are well developed at the time of birth. Weaning can take from one to three weeks after birth, with the young gaining independent mobility by week three. Juveniles remain with the group for up to two years (Aquino and Encarcion, 1986b, Greenberg, 1999). (Aquino and Encarnacion, 1986b; Bales, 1980; Greenberg, 1999)

  • Breeding interval
    Aotus nancymaae give birth 1 to 2 times yearly.
  • Breeding season
    Aotus nancymaae breed year round.
  • Range number of offspring
    1 to 3
  • Average gestation period
    133 days
  • Range weaning age
    12 to 15 days
  • Average weaning age
    13 days
  • Average time to independence
    18 days
  • Range age at sexual or reproductive maturity (female)
    211 to 400 days
  • Range age at sexual or reproductive maturity (male)
    211 to 400 days

Within the first week of birth, primary care is shared between the mother and father of the young. The mother provides milk and transportation while the father provides transportation and protection. After about the first week, primary care is given by the father. At this point, the only contact between mother and young is during feeding. When feeding is completed, the mother will bite the young until it returns to the father (Eisenberg and Redford, 1999, Greenberg, 1999). (Eisenberg and Redford, 1999; Greenberg, 1999; Eisenberg and Redford, 1999; Greenberg, 1999)

The care provided by the father in A. nancymaae is highly involved. Young are allowed to cling to either the stomach or the back of the father until free mobility is achieved. During this time, the father protects the young while sharing food with it. Young lose contact with the father only while feeding on milk from the mother (Bales, 1980, Greenberg, 1999). After independent mobility is achieved, the strong bond between father and offspring remains. It has been observed that the father of Aotus grooms, nurtures, and protects the young until they gain full independence. Although not observed, it has been noted that the father of A. nancymaae most likely plays with the young (Bales, 1980). (Bales, 1980; Greenberg, 1999)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male


Not enough information can be found on the lifespan of A. nancymaae.


Aotus nancymaae are social. They form small groups of two to five individuals who are all directly related. Competition for resources to create shelter results in strong territoriality within A. nancymaae groups, with individual groups not interacting with one another often. These groups occupy small territories, but the groups are still mobile within the territory (Aquino and Encarnacion, 1986b, Eisenberg and Redford, 1999, Greenberg, 1999). Trees used for foraging are the only areas in which the territories of A. nancymaae overlap. Groups defend their territories through aggressive vocalization and, if the need arises, with violence.

Aotus nancymaae sleep in carefully selected shelters during the day. These shelters are selected using four criteria: protection from predators, including concealment and multiple exits for easy escape; easy access for the individuals; shelter from the elements; and space enough to house the entire group together. These spaces include ready made lodgings such as holes in trees, concavities in branches, thickets, and branches which can be formed into shelters (Aquino and Encarnacion, 1986a). Because of the nocturnal nature of A. nancymaae, these shelters are shared with other organisms in the region with relatively little competition for space (Aquino and Encarnacion, 1986a, Greenberg, 1999, Moynihan, 1976).

During the night, A. nancymaae climb to the upper canopy to forage for food. (Aquino and Encarnacion, 1986b, Einsberg and Redford, 1999). (Aquino and Encarnacion, 1986a; Aquino and Encarnacion, 1986b; Eisenberg and Redford, 1999; Emmons, 1990; Greenberg, 1999; Moynihan, 1996)

  • Average territory size
    9200 m^2

Home Range

Groups of A. nancymaae have small home ranges, averaging about 9.2 ha (Eisenberg and Redford, 1999, Greenberg, 1999). This territory is well defined using scent marks (Aquino and Encarnacion, 1986a, Greenberg, 1999). Vocalization are used to show ownership of their territory. Physical force is rarely used to defend territory (Aquino and Encarnacion, 1986b). Slight overlapping of territories occurs commonly, but only includes fruit trees near the edges of territories. Small group sizes need smaller amounts of food, so the sharing of food sources does occur between groups (Aquino and Encarnacion, 1986b, Einsberg and Redford, 1999, Greenberg, 1999). The primary reason for the territoriality of A. nancymaae appears to be for shelters found within a territory. (Aquino and Encarnacion, 1986a; Aquino and Encarnacion, 1986b; Eisenberg and Redford, 1999; Greenberg, 1999)

Communication and Perception

Aotus nancymaae are very vocal. To remain in constant contact, groups of A. nancymaae constantly use a sequence of squeaks, whistles, and trills. Although this gives the group's position away, it allows for vital information to be passed rapidly through the group (Eisenberg and Redford, 1999, Moynihan, 1976). A slight raise in pitch allows for the communication of danger from predators (Eisenberg and Redford, 1999). Since communication is constant, all individuals in the group are aware of the warning and what it means. (Eisenberg and Redford, 1999; Moynihan, 1996)

These auditory signals are also used for territorial reasons. In defending a territory, individuals, usually juveniles, emit a series of squeaks, whistles and trills for 30-40 minutes. Rival groups respond in kind for longer periods from a distance no closer than 25 feet (Aquino and Encarnacion, 1986b, Einsberg and Redford, 1999, Greenberg, 1999). This exchange is the primary method of showing ownership of a territory. Subadults and solitary adults also emit high pitched squeaking while near or passing through claimed territory. It is believed that this communication is used for the attraction of mates (Greenberg, 1999, Moynihan, 1976). (Aquino and Encarnacion, 1986b; Eisenberg and Redford, 1999; Greenberg, 1999)

Aotus nancymaae use visual perception. Unlike many other nocturnal species, A. nancymaae lack a tapetum locitum, a light catching surface, in the eye. They also retain other diurnal characteristics such as the retention of several types of retinal receptors more useful in seeing higher light intensities. In order to see better at night, A. nancymaae have enlarged eyes allowing for more light to be received. Aotus nancymaae have developed accelerated nerve impulses to and from retinal receptors, allowing them to see more instantaneously. This allows for faster response times through sight, giving A. nancymaae the ability to see insects better and to improve perception while moving. An increased olfactory bulb indicates that smell is also used for perception (Greenberg, 1999). (Greenberg, 1999)

Food Habits

Aotus nancymaae are frugivorous, but, on occasion, feed on insects. Aotus nancymaae feed off of the fruit and the nectar of flowers of trees and insects in the region. They forage near the top of the canopy (Emmons, 1990, Greenberg, 1999, Moynihan, 1976). (Emmons, 1990; Greenberg, 1999; Moynihan, 1996)

  • Animal Foods
  • insects
  • Plant Foods
  • fruit
  • nectar
  • flowers


The toned down colors of the pelage of A. nancymaae is characteristic of many nocturnal species. This color scheme, along with being active only in the dark, makes it more difficult to see individuals. The large eyes and accelerated nerve signals allow A. nancymaae to see better and faster at night, allowing for better reaction to predator presence (Greenberg, 1999). Aotus nancymaae communicate constantly, allowing for individuals to know where each other are located and for notification of the presence of predators to be passed on quickly throughout the group (Eisenberg and Redford, 1999, Moynihan, 1976). The careful selection of sleeping nests is one more behavioral trait for predator evasion. Part of the criterion for choosing a nest is multiple exits for emergencies. This allows A. nancymaae to quickly evacuate their own nests without being cornered within (Aquino and Enccarnacion, 1986a). (Aquino and Encarnacion, 1986a; Eisenberg and Redford, 1999; Greenberg, 1999; Moynihan, 1996)

There is little information about predation on A. nancymaae. It is speculated that because of their nocturnal nature, strong vocal behavior, and ability to find and defend sufficient shelter, A. nancymaae are a difficult prey to hunt (Aqunia and Encarnacion, 1986a, Greenberg, 1999). Large, arboreal snakes may be their primary predators. (Aquino and Encarnacion, 1986a; Greenberg, 1999)

  • Known Predators
    • large, arboreal snakes (Serpentes)

Ecosystem Roles

Aotus nancymaae are frugivores and may help to disperse seeds to a small extent. Living in groups of 2 to 5 individuals and having a population density of 8 to 10 groups per square kilometer, the population density hardly exceeds 20 individuals pre square kilometer. With a low basal metabolic rate, A. nancymaae require little food per individual (Aquino and Encarnacion, 1986a, Eisenberg and Redford, 1999). Aotus nancymaae do not impact food sources substantially because of the combination between this low population density and low food consumption. (Aquino and Encarnacion, 1986a; Eisenberg and Redford, 1999)

Strong defensive behaviors, both nocturnally and diurnally, make A. nancymaae less desirable prey (Bales, 1980, Eisenberg and Redfield, 1999, Moynhan, 1976). Being nocturnal, A. nancymaae share territory with diurnal species with little competition. (Bales, 1980; Eisenberg and Redford, 1999; Moynihan, 1996)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Ma's night monkeys are sometimes used in medical research (Greenberg, 1999).

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no negative impacts of A. nancymaae on humans.

Conservation Status

There is little information on the conservation status of A. nancymaae

Other Comments

Until 1982, the genus Aotus was considered to have only one species, A. trivirgatus. After observing the large variance in reaction to diseases such as malaria amongst individuals of Aotus, it was suggested that the genus consisted of several species (Hershkovitz, 1983). Now, after much molecular research and many field studies, ten species are recognized, including A. nancymaae. However, some researchers recognize only one species still A. trivirgatus (Emmons, 1990). (Eisenberg and Redford, 1999; Emmons, 1990; Hershkovitz, 1983)

Ma's night monkeys are domesticated and associated with human settlements in areas they inhabit.


Tanya Dewey (editor), Animal Diversity Web.

John Graf (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), 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


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


to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species


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.


union of egg and spermatozoan


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


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.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born


Aquino, R., F. Encarnacion. 1986. Characteristics and use of sleeping sites in Aotus (Cebidae: Primates) in the Amazon lowlands of Peru. American Journal of Primatology, Vol. 11 Issue 4: 319-331.

Aquino, R., F. Encarnacion. 1986. Population structure of Aotus nancymai (Cebidae: Primates) in Peruvian Amazon lowland forest. American Journal of Primatology, Vol. 11 issue 1: 1-7.

Bales, K. 1980. Cumulative scaling of paternalistic behavior in primates. American Naturalist, Vol. 116: 454-461.

Eisenberg, J., K. Redford. 1999. Mammals of the Neotropics Volume 3. Chicago: University of Chicago Press.

Emmons, L. 1990. Neotropical Rainforest Mammals: A Field Guide. Chicago: University of Chicago Press.

Greenberg, J. 1999. "MIFOUs and Night Monkeys: Paternal care on Aotus sp." (On-line pdf). Accessed March 22, 2006 at

Hershkovitz, P. 1983. Two new species of night monkeys, genus Aotus (Cebidae, platyrrhini): A preliminary report on Aotus taxonomy. American Journal of Primatology, Vol. 4 Issue 3: 209-243.

Moynihan, M. 1996. The New World Primates: Adaptive radiation and the Evolution of Social Behavior, Language, and Inteligence. Princeton, New Jersey: Princeton University Press.