Preuss's Monkey

Preuss's Monkey is a forest-dwelling guenon native to the Cameroon Highlands and Bioko Island. It is one of the least known African primates, inhabiting montane and lowland rainforests at relatively high elevations. The species is remarkable for its restricted range, striking blue-grey coat, and status as an endangered primate threatened by intense hunting pressure. It plays an important ecological role as a seed disperser in its forest habitat.

Cameroon, Nigeria, Equatorial Guinea (Bioko Island)

Found in the Cameroon Highlands including Mount Cameroon, the Bakossi Mountains, and adjacent areas in southeastern Nigeria (Cross River region), as well as Bioko Island in Equatorial Guinea, part of the Cameroon volcanic line.

Altitude and depth

Approximately 200-2200 meters, with populations most concentrated in montane forests between 900-1800m.

Seasonal movements

No true migration or hibernation; some seasonal shifts in ranging patterns and diet occur in response to fruiting cycles during wet and dry seasons.

Primary and secondary montane and submontane tropical rainforest, including cloud forest at higher elevations. Also found in lowland rainforest on Bioko Island. Prefers dense canopy cover with continuous forest structure.

Adaptations to its environment

Strong limbs and prehensile grip adapted for arboreal locomotion through dense montane canopy. Thick fur provides insulation at higher, cooler elevations. Cryptic coloration helps avoid detection by predators and hunters.

Classified as Endangered (EN) by the IUCN due to a suspected population decline of over 50% over the past three generations, driven primarily by hunting and habitat loss.

Estimated population

Exact numbers are unknown but populations are estimated to be declining across all range areas; considered rare and patchily distributed, with the Bioko population also under significant threat.

Intense bushmeat hunting, habitat destruction from logging and agricultural expansion, and forest fragmentation are the primary threats. Civil unrest in parts of its range has also increased poaching pressure.

Diseases and parasites

Susceptible to various gastrointestinal parasites and potentially some primate-specific viral diseases, though specific studies on this species are limited.

Protected within some reserves including Mount Cameroon National Park and Korup National Park; listed on CITES Appendix II. Conservation organizations conduct monitoring and anti-poaching patrols in parts of its range, particularly on Bioko Island.

Recommended actions

Strengthen enforcement of anti-poaching laws, expand and connect protected forest areas, conduct population surveys to better estimate numbers, and engage local communities in conservation and alternative livelihood programs.

The coat is predominantly dark grey to blue-grey with a distinctive black face bordered by a white or pale band. It has a long tail and relatively short limbs adapted to arboreal life. The underparts are often lighter than the dorsal coloration.

Size

Head-body length approximately 45-60 cm, with a long tail typically extending 55-80 cm.

Weight

Males typically weigh 4-6 kg; females are smaller, weighing around 3-4 kg.

Distinctive features

Distinguished from related guenons by its unique blue-grey pelage, black face with a pale brow band, and its specific montane habitat preference within the Cameroon Highlands.

Differences between males and females

Males are noticeably larger than females, with more prominent canine teeth, though coloration is similar between sexes.

Lives in social groups typically comprising one adult male and several females with offspring, though group composition can vary. Group sizes generally range from 5 to 20 individuals.

When it is active

Diurnal, being most active during daylight hours foraging in the forest canopy and resting during midday heat.

Diet

Omnivorous diet consisting mainly of fruits, leaves, seeds, and flowers, supplemented occasionally with insects and other small invertebrates.

Communication

Uses a range of vocalizations including alarm calls and contact calls to coordinate group movement and warn of predators. Body postures and facial expressions are also important for social communication.

Interactions with other species

Predators include large raptors, leopards, and occasionally humans through hunting. May share habitat and sometimes forage alongside other primate species such as mangabeys and other guenons.

Role in its ecosystem

Plays a key ecological role as a seed disperser, helping maintain forest regeneration and plant diversity within its montane habitat.

Breeding is not strictly seasonal, though births may peak during periods of higher fruit availability. Gestation lasts approximately 5-6 months, typically resulting in a single offspring.

Raising the young

Females provide the majority of parental care, including nursing and carrying infants until they become more independent at several months of age. Other group females may also assist in alloparental care.

Maturity and lifespan

Sexual maturity is typically reached around 4-6 years of age. Lifespan in the wild is estimated at 20-25 years, potentially longer in captivity.

Classification

Class Mammalia > Order Primates > Family Cercopithecidae > Genus Allochrocebus > Species Allochrocebus preussi

Subspecies

Two subspecies are generally recognized: Allochrocebus preussi preussi (mainland Cameroon and southeastern Nigeria) and Allochrocebus preussi insularis (Bioko Island, Equatorial Guinea).

Scientific synonyms

Cercopithecus preussi (former genus placement before reclassification into Allochrocebus)

Recent studies

Recent taxonomic revisions have reclassified this species from genus Cercopithecus to the newly established genus Allochrocebus based on molecular phylogenetic studies.

Compared with similar species

Closely related to other members of the former 'l'Hoest group' such as Allochrocebus lhoesti and Allochrocebus solatus, but distinguished by its distinct coloration and more restricted montane range.

Preuss's Monkey is named after German naturalist Paul Preuss who first collected specimens in Cameroon. It is one of the rarest and least studied African guenons, with much of its ecology still poorly documented.

Where and how to see it

Best observed in protected montane forests such as Mount Cameroon National Park during early morning hours when the species is most active and vocal. Patience and quiet movement are essential due to its shy and elusive nature.

Risks to humans

No notable risk to humans; the species is shy and avoids direct contact with people.

Human uses

Hunted locally for bushmeat, contributing to its population decline; not commonly used in trade or traditional medicine.