Cercopithecus hamlyniowl-faced monkey

Geographic Range

The owl-faced monkey is found in eastern Africa, in the area formerly known as Zaire and now called the Democratic Republic of Congo. They are also found in the extreme northwest of Rwanda and the extreme southwest of Uganda. This region has natural borders (rivers and lakes, rainforests, and a volcano range) surrounding it on all sides making it unlikely that this species will ever expand its range.


The primary habitat of C. hamlyni is dense bamboo forest. These monkeys exist at elevations of 900-4554m. They live in a rainforest region surrounded by natural borders. Lakes and river systems, rainforests, and a volcano range define the edges of their range.

Physical Description

The owl-faced monkey, or Hamlyn's monkey, is a sexually dimorphic species; the males are typically larger than the females. The average body length for an adult male is 50-65 cm with an average weight range from 7-10 kg. Females have an average body length of 40-55 cm and an average weight from 4.5-6 kg.

The coat of an adult Cercopithecus hamlyni is olive gray and black. The coat is darkest along the underbelly and along the underside of their hindlimbs and arms. It is black in these areas. An olive gray tint appears on the backs of adults. Their nearly monotone coat aids in rendering them nearly undetectable to predators. The fur on these animals is long, dense, and fine.

The face of an adult owl-faced monkey is its most distinguishing feature. These primates have a horizontal stripe across their browridge and a vertical stripe from the center of the brow to the lip area. These two stripes range in color from yellow-cream to white and form a T-shaped facial marking.

Newborns of this species initially have a yellow-brown coat and later develop a thin black ring of fur around their faces. Gradually, the coloring of these newborn coats will darken and become like that of an adult.

Both male and female adult owl-faced monkeys have bare, blue-skinned buttocks and genital regions. The male genitalia are usually very bright due to the blue scrotum and reddish-pink penis. Adolescent males do not have as brightly colored genitalia as mature males. In captivity it has been observed that the brightness of male genitalia in owl-faced monkeys is indicative of the animal's degree of sexual maturity.

Owl-faced monkeys have unique hands and feet in that they posses elongated phalanges. These allow them to have a strong grip, which is a useful adaptation for traveling on wet bamboo.

  • Sexual Dimorphism
  • male larger
  • Range mass
    4 to 10 kg
    8.81 to 22.03 lb


The birth season for C. hamlyni is from May to October. The gestation period is around five to six months. These monkeys have one offspring at a time. Twin births occur on rare occasions. There is generally a two year interval between births. Young are born with pink faces, which darken as they mature.

  • Breeding interval
    There is generally a two year interval between births.
  • Range number of offspring
    1 to 2
  • Range gestation period
    5 to 6 months
  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female
  • extended period of juvenile learning



These monkeys live in groups of under ten individuals. Within these small groups, there is one dominant male. Because they live in small social groups in dense cover, their home range can be relatively small. This is possible due to the abundance of food present in this densely forested region. Predators of the owl-faced monkey are leopards, golden cats, and human hunters.

Communication by C. hamlyni is both vocal and olfactory. In order to maintain their home ranges, owl-faced monkeys mark their territory with their own scent. An apocrine chest gland, present in both males and females, is the source of this personal scent. It is in this manner that owl-faced monkeys can identify each other's territory. Continual scent marking behavior is necessary due to the wet environment of this species.

Vocal communication serves as an orientation device and a source of affiliation within this dense habitat. Predators are not alerted by these vocalizations because these calls are quiet relative to other species. Owl-faced monkeys also use vocal communication to serve as mating calls.

This diurnal monkey is described as both terrestrial and arboreal. Their foraging strategy provides them with a unique ability for slow, vertical climbing, although they most commonly feed and travel by terrestrial means.

Communication and Perception

Food Habits

Owl-faced monkeys feed on bamboo shoots. These grow well during the long wet seasons. Also available for their consumption are leaves and shoots of other trees, scrubs, and herbs throughout the year, especially Peucedanum (wild celery). These monkeys also eat fruits, including perennial blackberries, and a few other plants that produce seasonal fruits or seeds.

  • Plant Foods
  • leaves
  • fruit

Economic Importance for Humans: Positive

A refugee movement has occurred as a result of war and revolt. Because of the geographic location of its range, this species exists in an area through which many refugees flee. These starving refugees hunt owl-faced monkeys for food. C. hamlyni is also hunted throughout its range for money in the 'bushmeat' trade.

Conservation Status

Because expanding out of their existing range seems highly unlikely due to natural barriers, the small habitat in which C. hamlyni survives is vital to their existence. This area is unprotected from hunting and deforestation. With human hunters as their greatest threat, owl-faced monkeys are becoming increasingly vulnerable to extinction. Another reason these animals are classified as vulnerable is due their slow birth rate.

There are owl-faced monkeys in many zoos including those in San Diego, San Francisco, Philadelphia, and in Europe. However, the possibility of their extinction is only magnified by the poor and unsuccessful reproduction rates that have been recorded in captivity.

Other Comments


The scientific name Cercopithecus hamlyni literally means Hamlyn's cercopithecine. Hamlyn's monkey or Hamlyn's owl-faced guenon are other common names for this monkey. These names are derived from a well known animal dealer who, in 1907, brought the first C. hamlyni into captivity at the London Zoo. In French and German, these monkeys are described as being 'owl-headed'.


Nancy Shefferly (editor), Animal Diversity Web.

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



living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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

  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates


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.


an animal that mainly eats leaves.


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 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.


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.

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


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


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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uakari@discoverymail.com, "Primate Behavior: Hamlyn’s Monkey (Cercopithecus hamlyni)" (On-line). Accessed November 30, 1999 at http://members.tripod.com/uakari/cercopithecus_hamlyni.html.