Geographic Distribution and Habitat
The Preuss’s Monkey (Allochrocebus preussi) is a species of Old World monkey living in various regions in southwest Cameroon and southeast Nigeria and in Equatorial Guinea. This species comprises two subspecies: the Cameroon Preuss’s monkey (A. p. preussi) found on the mainland, and the Bioko Preuss’s monkey (A. p. insularis) found only on Bioko Island, in Equatorial Guinea.
With an average of 79–345 inches (200–900 cm) of rainfall annually, Preuss’s monkeys live in some of the wettest places in Africa. They are most abundant in montane and sub-montane forests, at least 8,200 feet (2,500 meters) above sea level and are rarely found below 2,600 feet (800 meters). As such, they are found with some certainty in the Cameroon Highlands and along the slopes of Mount Cameroon. Some populations live in various and isolated forest patches within montane grasslands as well. The subspecies on Bioko Island is particularly fond of the Schleffera forests found around Pico Basilé, the island’s highest point, and in the Gran Caldera Scientific Reserve.
Altitude and the amount of forest coverage in a region tend to restrict populations’ movements and, in some cases, keep them virtually separate from others.
Size, Weight, and Lifespan
A Preuss’s monkey has a relatively large body weighing, on average, 22 pounds (10 kg). Males tend to be the bigger sex, ranging from 16.5 to 27.6 inches (42–70 cm) in length, whereas females are only 14.5–21.6 inches (37–55 cm) on average.
Individuals have been estimated to live up to 31 years in the wild.
Meat from wildlife species that are hunted for human consumption, generally in tropical forests.
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A Preuss’s monkey has a unique, Shakespearian-looking collar of silvery white fur at the base of his neck. His dark gray face is framed by tufts of lighter gray fur. The crown of his head, his shoulders, his flanks, his thighs, and the middle section of his tail are also dark gray with silvery flecks. Most of his body is black except for his back, which is a reddish brown color. His scrotum is bright blue in color.
Except for such flamboyant genitals, female Preuss’s monkeys have essentially the same appearance as males.
Preuss’s monkeys are largely frugivorous, with roughly half of their diet consisting of fruit. Another quarter of the time, they munch on tree shoots.
When fruits and tree shoots are unavailable, they forage for other plants, like certain herbs growing in their ecosystem. Young leaves and flowers may also find their way into their diet, but with far less frequency than their more preferred plant matter.
Occasionally, they might chow down on an insect or two.
Behavior and Lifestyle
Preuss’s monkeys are diurnal and spend their days eating, resting, and socializing with others in their troop. Their semi-terrestrial lifestyle means they spend a lot of time on the ground. However, their meals are mostly taken in the understory, where they graze on fruit.
Preuss’s monkeys are rather shy and elusive creatures. Additionally, their uniquely quiet nature compared to other forest-dwelling primates, as well as their preference for higher altitudes, makes them a difficult species to locate, and therefore to study, in the wild.
Shy, elusive, and living in remote montane forests, Preuss’s monkeys are a difficult species to research in the wild.
Until 2013, Preuss’s monkeys were treated under the genus, Cercopithecus and, as such, are sometimes also called Preuss’s guenons.
As Preuss’s monkeys can be hard to locate in the wild, researchers still have a lot to learn about their daily rituals and group politics.
Groups of Preuss’s monkeys consist of 9 to 12 members, typically a single adult male plus several females and their infants. Occasionally, more adult males are present.
In select areas, groups of Preuss’s monkeys have been known to socialize with groups of Putty-nosed monkeys (Cercopithecus nictitans).
Like other social primates, Preuss’s monkeys have developed ways to communicate with each other that include vocalizations, body language, and facial expressions. A female or juvenile makes a soft, atonal “uh” sound in order to keep other members of the troop privy to their movements. A males makes a different sort of contact call. His is a louder “boom.” Preuss’s monkeys are relatively quiet monkeys, however, and are not known to not use vocalizations to the extent that other forest-dwelling primates often do.
Body language, facial expressions, and other methods of communication used by Preuss’s monkeys are topics that still await research.
Most groups of Preuss’s monkeys have one male who likely mates with the females of his troop—but since they are difficult to locate and study in the wild, much has yet to be determined about this species’s mating rituals.
As fruit and seed eaters, Preuss’s monkeys likely play a role in the dispersal of seeds in their ecosystem. However, the extent to which they do has not been researched. Little is known regarding their ecological role and specifics may vary between subspecies or even separate monkey troops.
The Preuss’s monkey is classified as Endangered by the International Union for Conservation of Nature (IUCN, 2018), appearing on the IUCN Red List of Threatened Species.
Primates around the world are threatened by human activities that destroy their natural habitats, and the situation for Preuss’s monkeys is no different. Logging and agricultural practices in Cameroon and Nigeria have had adverse effects on these mainland populations. Though most of these monkeys live at higher altitudes where crops are virtually ungrowable, much of the once-intact highland forests they call home has been converted into grazing land for cattle.
Coffee is one of Cameroon’s biggest exports, and its cultivation has played a key role in the country’s deforestation as well. In the 1980s and 1990s, the rise in the price of coffee around the world initiated rapid clearing of their forests. Even after coffee prices fell again, farmers hopeful for another price spike meant that these practices continued unabated. As a result, the scant amounts of montane forests that would be prime habitat for Preuss’s monkeys now exist mostly in separate and small patches.
Forest loss in Cameroon was higher in 2014 than all previously recorded years, and still shows no signs of waning. Until they are properly protected, it is only a matter of time before these few refuges are also destroyed by human activities.
Preuss’s monkeys are also greatly threatened by bushmeat hunting. As a semi-terrestrial and relatively large-bodied species, they are particularly susceptible to human predation. For a long time, the remoteness of their habitats kept them relatively protected. However, as forests have diminished and new roads have been built, these natural defenses have proven less effective.
Though hunting is a threat to both subspecies, the situation has become particularly bad for the Preuss’s monkeys on Bioko Island. Even in the island’s protected areas around Pico Basilé and the Gran Caldera Scientific Reserve, hunting has increased in the last twenty years as new roads being built have given hunters easier access to their once-remote habitats.
In spite of easier access to their habitats, researchers still struggle to find populations of Preuss’s monkeys in the wild. Surveys of regions where this species was once considered common have sometimes turned up zero sightings. Such findings paint a bleak picture for this species. So much remains unknown about this shy and elusive species that the inability to do research on them presents its own kind of threat. Unless researchers are able to start filling in the blanks soon, the measures that best serve their conservation may never become known.
Today, this species lives in multiple protected areas on mainland Africa and on Bioko Island. However, better monitoring and enforcement of these protections are direly needed.
Preuss’s monkeys are listed under Appendix II of the Convention on International Trade in Endangered Species (CITES) and as a Class B species under the African Convention. They are protected nationally in Cameroon as well as locally in Cross River State in Nigeria. Additionally, by presidential decree, the hunting, sale, and consumption of primates is illegal in Equatorial Guinea.
Much remains unknown about the Preuss’s monkey’s population size, distribution, life history, and ecological role. Until this information is researched, the best methods for conserving this species will also remain unknown.
Written by Zachary Lussier, February 2021