The owl-faced guenon is thought to be largely terrestrial, spending most of its time on the ground (4) (6). It has two peaks of daily activity; one in the early morning, and then again in the late afternoon or evening (7). Living in small groups with a single male (2), the owl-faced guenon is apparently territorial, but avoids serious conflicts with neighbouring groups (7). This omnivorous monkey feeds on fruit, insects and leaves (2). Its fairly large incisors are perfect for biting into fruit, and the flatter molars are suited to crushing and grinding hard seeds. It also possesses cheek pouches, the advantages of which are twofold: in areas where competition for fruit is intense, the monkey can grab as much food as possible before being supplanted by another hungry monkey, and at the same time, enzymes in the saliva help break down toxic compounds in unripe fruits and seeds stored in the pouches (8).

The owl-faced guenon is an unusual-looking monkey whose large, round head, triangular face and large eyes give it a somewhat owl-like appearance. The name 'guenon' is given to a group of monkeys with distinctive 'moustaches', light nose spots or striped sideburns (4). The owl-faced guenon has a silky, olive coat, a black face with a yellowish patch above the brow, and a thin, white stripe running down the nose. The long tail is ash-grey and ends in a black tassel, and the rear end and scrotum of the guenon are bright blue (2) (4). Two subspecies have been described in the past, Cercopithecus hamlyni hamlyni and Cercopithecus hamlyni kahuziensis (5), but the status of C. h. kahuziensis is now in doubt (1) (6), and, as such, it is not currently recognised as a distinct subspecies, pending further investigation (1).

This species ranges from the the eastern Democratic Republic of the Congo, where it is found in lowlands from the Congo/Lualaba River to the Ituri Forest and into the Albertine Rift and Nyungwe Forest in Rwanda. It occurs north to the Lindi-Nepoko river system and south to the southern tropical moist forest limit, where its range limit is poorly defined. Although it is generally a lowland species, it also occurs in the mountains of Albertine Rift, where many records come from the bamboo zone. The easternmost highland populations of C. hamlyni are now isolated in fragmented habitat islands and some have been extirpated (e.g., Gishwati, Rwanda, the Virunga Volcanos, and forest islands between Kahuzi-Biega National Park and Massisi). The species occurs above 3,000 m in both Tshiberimu and Kahuzi, so it seems safe to assume that 3,200 m is the upper elevation limit.

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.

Biogeographic Regions: ethiopian (Native )

The owl-faced guenon occurs in eastern Democratic Republic of the Congo, northwestern Rwanda, and Uganda (1) (2) (6).

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.

Range mass: 4 to 10 kg.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Habitat and Ecology

Systems

• Terrestrial

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.

Terrestrial Biomes: rainforest

The owl-faced guenon primarily inhabits dense montane rainforest, but can also occur in lowland forest (5).

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

Primary Diet: herbivore (Folivore )

Average lifespan

Sex: male

Status: captivity: 27.0 years.

Maximum longevity: 28.6 years (captivity)

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.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

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

Year Assessed

Assessor/s

Reviewer/s

Justification

History

• 1996
  Lower Risk/near threatened
• 1994
  Vulnerable
  (Groombridge 1994)
• 1990
  Vulnerable
  (IUCN 1990)
• 1988
  Vulnerable
  (IUCN Conservation Monitoring Centre 1988)
• 1988
  Vulnerable
• 1986
  Insufficiently Known
  (IUCN Conservation Monitoring Centre 1986)

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.

CITES: appendix ii

IUCN Red List of Threatened Species: vulnerable

Classified as Vulnerable (VU) on the IUCN Red List (1), and listed on Appendix II of CITES (3).

Population

Population Trend

Major Threats

Guenons are vulnerable to both the bushmeat trade and human disruption of forests. Destruction of forest habitat throughout its range continues due to agricultural expansion and logging (7). Logging operations result in an increase in workers in the area, causing an increased demand for bushmeat, and logging roads make remote forests more accessible to hunters seeking meat to sell in local markets. In central and west Africa, a guenon carcass can fetch the equivalent of US $5 (8). Forests surrounding Mount Kahuzi are under increasing pressure from rapidly rising human populations. An influx of Rwandan refugees in 1994 and rebel soldiers from 1997 resulted in widespread forest clearance for agriculture and hunting (9). The year 2000 also saw a rush for the valuable industrial mineral coltan, which attracted more than 10,000 miners to the Kahuz-Biéga National Park in which Mount Kahuzi lies, and led to drastic deforestation and poaching (9).

Conservation Actions

The owl-faced guenon can be found within a small number of protected areas, such as the Okapi Faunal Reserve and the Kahuzi-Biéga National Park in the Democratic Republic of Congo (9) (10), but, as mentioned above, these generally offer only nominal protection. This species is likely to benefit from the increased protection and management of these areas, but at present, the situation in this volatile region is often too dangerous for action to be taken.

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.