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Aotus Azarai - Azara's Night Monkey

Physical Description:

Aotus azarai is a New World Monkey.  It is commonly referred to as night, owl, or dourocouli monkey.  They are one of the smallest monkeys in the Cebidae family, and they are members of the Aotinae subfamily.  There are ten species in the Genus Aotus.  There are two distinguishable groups based on color, karyotype, and pelage (Hershkovitz 1983).  One group includes the gray-necked species; A. brumbacki, A. lemurinus, A. trivirgatus, A. hershkovitzi, and A. vociferans.  The A. nancymai,  A. miconax,  A. infulatus,  A. nigriceps,  and A. azarai are in the red-necked species group.  A. azarai or A. azarae includes two subspecies, Aotus azarai bolivionsis and Aotus azarai azarai.  These subspecies have different distributions in South America, and their physical features enable them to be well-adapted to their particular habitat.

Aotus azarai monkeys weigh very little, which makes locomotion through the canopy more feasible.  Because the monkeys are small and light, they do not require a prehensile tail.  Their tail length ranges from about 316-400 mm, and their body head length is approximately 240-370 mm.  A. azarai have large eyes with rods in the retina that detect color.  They have short, thick pelage and small ears.  Their coloration is grayish with a brownish/reddish stripe along the side of the body.  Their brown face has white eye circles.  A throat sac is found under the chin, which is used for vocalization.  This is no baculum in this species.

Their tooth morphology is well-adapted to their omnivorous diet, which includes fruits, insects, small vertebrates, leaves, seeds, flowers, gums, eggs, and bark.  They have 36 teeth (I 2/2, C 1/1, P 3/3, M 3/3), and they have bunodont cheek teeth.  There are 4 cusps on their upper molars and 4-5 cusps on their lower molars.  They exhibit a platyrrhine nose-shape.  The monkeys have nails on their digits, and the large toe of the hind foot is opposable.  All of these characteristics aid in their feeding, locomotion and social behaviors.


Aotus are found in Neotropical South America.  The gray-necked group is found north of the Amazon, and the red-necked group is found south of the Amazon.  The Aotus azarai range includes Bolivia, Paraguay, and northern Argentina.  South of Rio Bermejo and east from the Rio Paraguai to the Andes is the area inhabited by the southern A. azarai in Argentina (Smith 1999).  A. azarai bolivionsis is found in the northern region, whereas A. azarai azarai is found in the southern region.  The regions are separated by land barriers from Lago Uberaba to Sucre, Bolvia (Smith 1999).

Ontogeny and Reproduction:

Aotus azarai do not exhibit sexual dimorphism.  Their gestation period is 126-133 days.  They give birth to 1-2 young, which weigh approximately 3 ounces.  Lactation usually lasts from 5-12 months.  Night monkeys have an interbirth period of approximately 1 year.  Usually, groups of night monkeys consist of a monogamous breeding pair and their young. The male tends to actively participate in the raising of offspring.  While the young clings to the mother initially, the father carries the offspring from the 3rd week until the 4th or 5th month.  Siblings tend to care for the young if the father dies (SBRR 2004).  The young are considered sexually mature at 2 years old.  Studies show that most offspring leave shortly after maturation, although some remain with their parents into their 4th year (Fernandez-Duque et al. 2002).  Night monkeys may live up to 20 years. 

Ecology and Behavior:

Groups of A. azarai usually consist of 3-4 individuals but are sometimes as large as 7 animals (Fernandez-Duque et al. 2001).  Data indicates that species living in the subtropics are comparable to those of the tropic regions (Fernandez-Duque et al. 2001).  Aotus communicate through loud owl-like hoots and grunts that emanate from their laryngeal sacs.  Glandular and urine scent markings are prevalent within the species, which demonstrates olfactory communication.

A. azarai inhabit the trees of their Neotropical regions, and they seldom leave the canopy.   In Bolivia, night monkeys establish sleeping sites in the middle strata of the forest which consist of liana platforms and branches.  These are found at a mean height of 10.8 meters in trees with a mean height of 12.8 meters (Garcia and Braza 1993).  Bird nests and other materials may be used to supplement the sleeping site.  The locations of the sleeping sites may be relative to food availability and protection against predation (Garcia and Braza 1993).

Night monkeys may forage either during the day or at night.  Many of the species of A. azarai are nocturnal, avoiding predation from such animals as the great horned owl.  Being active at night not only reduces the threat of predators, but also reduces competition from diurnal species.  Nocturnal species tend to spend their lives in the canopy, and they become more active as the moon becomes brighter (SBRR 2004).  It is hypothesized that they travel memorized routes at night (SBRR 2004).  The species A. azarai azarai, found in Paraguay and Argentina, tend to be diurnal (Fernandez-Duque 2003).   Their diets vary from other Aotus in that they feed on the seeds of Brosimum alicastrum (SBRR 2004).  They also eat more leaves during the cold season in Paraguay than other Aotus species.  The night monkeys of Argentina eat more fruits and flowers (SBRR 2004).  In general, night monkeys are frugivores, although they may also feed on leaves, small vertebrates, bird eggs, and arthropods.


Aotus azarai is a CITES-listed species (SI 1993).  Habitat destruction has impacted its survival rates.  Other human impacts include the killing A. azarai for fur or food, and the collection and use of the monkeys for medical research.   The monkeys are highly adaptable to new environmental surroundings, but there has been some research indicating that colder temperature changes may impact A. azarai behaviors or populations (Smith 1999).

Aotus species self-anoint with millipedes and plants.   Aotus have been observed self-anointing with garlic, onion, chives, live millipedes, millipede-produced benzoquinones and P. marginatum leaves (Zito et al. 2003).  They grasp and rub the material on their fur for 20-minute intervals.  Studies support the hypothesis that self-anointing may deter insects (Baker 1996).

Taxonomic classification of A. azarai can be found in the ITIS Report (2004).

Literature Cited:

Baker, M.   1996.   Fur rubbing:  use of medicinal plants by capuchin monkeys (Cebus capucinus).  American Journal of Primatology 38:  264-270.

Fernandez-Duque, E.  2003.   Influences of moonlight, ambient temperature, and food availability on the diurnal and nocturnal activity of owl monkeys (Aotus azarai).  Behavioral Ecology and Sociobiology 54(5): 431-440.

Fernandez-Duque, E. and C. Huntington.  2002.  Disappearances of individuals from social groups have implications for understanding natal dispersal in monogamous owl monkeys (Aotus azarai).  American Journal of Primatology 57(4): 219-225.

Fernandez-Duque, E., M. Rotundo and C. Sloan.  2001.  Density and population structure of owl monkeys (Aotus azarai) in the Argentinean Chaco.  American Journal of Primatology 53(3): 99-108.

Garcia, J. E. and F. Braza.  1993.  Sleeping sites and lodge trees of the night monkey (Aotus azarae) in Bolivia.  International Journal of Primatology 14:  467-477.

Hershkovitz, P.  1983.  Two new species of night monkeys, Genus Aotus (Cebidae, Platyrrhini): a preliminary report on Aotus taxonomy.  American Journal of Primatology 4:  209-243.

ITIS Report.  2004.  ITIS Standard Report Page: Aotus azarai.  <>.  Accessed 22 September 2004.

 SBRR.  2004.  Saimiri Breeding and Research Resource.  <http://www.saimiri.usouthal.eduaotus_natural_history.htm>.  Accessed 23 November 2004.

Smith, C. 1999. "Aotus azarai", Animal Diversity Web.  < Aotus_azarai.html >.  Accessed 19 September 2004.

Smithsonian Institute (SI). 1993. Mammal Species of the World.  <>.  Accessed 19 September 2004.

Zito, M., S. Evans and P. J. Weldon.  2003.  Owl monkeys (Aotus spp.) self-anoint with plants and millipedes.  Folia Primatology 74:  159-161.

Reference written by Kim Moore, Biol 578 (Mammalogy), University of Wisconsin – Stevens Point:  Edited by Chris Yahnke. Page last updated July 25, 2005.

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