Allen's Swamp Monkey

Allen's swamp monkey is a medium-sized Old World monkey found only in swamps and riverside forests of the central Congo Basin. It has a coarse coat of green, brown, gray and white fur, and adults reach a head-body length of up to 46 cm, with a tail slightly longer. It is an omnivore that lives mostly in trees beside water, coming down to the ground to forage for invertebrates and plant matter. Active by day and highly social, it lives in groups of more than 40 animals. It was once classed as a guenon but has been placed in its own genus, Allenopithecus, since the 1920s.

About the Allen's swamp monkey

Allen's swamp monkey (Allenopithecus nigroviridis) is a medium-sized Old World monkey that lives in the swamp forests and riverside forests of the central Congo Basin in Africa. Once classed as a guenon, it is now the only member of its own genus, a sister group to the guenons, and it keeps many primitive traits shared with baboons and macaques.

The species is named after the American zoologist Joel Asaph Allen. It is also called the swamp guenon, the blackish-green guenon and Allen's baboon-like monkey. It was first described in 1907 as Cercopithecus nigroviridis, from the skin of a young female from the upper Congo River, and was moved to its own genus, Allenopithecus, in 1923.

Its body is stocky and robust, unlike the slender build of most guenons. Head-and-body length reaches 46 cm (18 in), and the tail is only slightly longer. Males are much bigger than females, weighing up to 6.0 kg (13.2 lb) against the female's 3.7 kg (8.2 lb). The skeleton is built for moving both in trees and on the ground, and when it stands on all fours its posture resembles a baboon's.

One unusual feature is its hands. Apart from the free thumb, the fingers are webbed at the base, which may be an adaptation to a partly aquatic life. The coat is coarse, in shades of gray, green and yellow, with yellowish tinges on the head, neck, shoulders and back, pale fur on the chin, chest, belly and inner limbs, and a darker tail. The face is dark except for pale cheeks, and the pointed ears look more like a macaque's than a guenon's. Like other monkeys in its subfamily, it has cheek pouches for storing food. Newborns have a crown of silky white hair and a yellower coat, which is fully replaced by 10 weeks of age.

Behavior and diet

Allen's swamp monkey is diurnal and social. It lives in groups of more than 40 monkeys that include several adult males and females, though smaller groups may have only one adult male. Members groom each other to strengthen social bonds and communicate with gestures and calls, using chirps as warnings. Males and females interact only rarely, a guenon-like trait, while group size and makeup resemble those of baboons.

It spends most of its time in trees but comes down to the ground and into shallow water to forage. Its diet is unusual for a primate. Along with fruit, seeds, leaves, nectar and flowers, it eats small animals such as shrimp, fish, snails and worms. Food takes 23 to 24 hours to pass through its gut, longer than expected for a monkey its size.

There is no breeding season, and babies are born throughout the year after a gestation of five to six months. Females usually have a single baby, though twins have been seen, and mothers do most of the caregiving. An infant first leaves its mother at about two weeks old, tries solid food at about 33 days and is weaned at two and a half months. In captivity, infants rather than mothers drive the separation, and mothers are more relaxed about distance than tree-dwelling guenon mothers, possibly because a fall is less dangerous for a monkey that spends time on the ground.

Captive studies describe the species as social and friendly, similar in behavior to guenons. Lifespan figures vary: some accounts give up to about 20 years, while an average of 28 years has also been reported.

Range and habitat

Allen's swamp monkey lives in the Congo Basin between about 16°E and 24°E, from about 4°N to possibly 6°S. Its range covers parts of the Republic of the Congo and the Democratic Republic of the Congo, and it may also occur in Cameroon and Angola. It was recorded north of Bayanga in the Central African Republic in 2016.

Before the 1990s, it was thought to live only in swamps and riverside forests along the lower Likouala-aux-Herbes, Oubangui and Sangha rivers. A separate population was confirmed on the upper Sangha in 2006, about 100 km (62 mi) northwest of the known range. Studies in the Lomako Forest found it only in swamp forest, unlike many other monkeys there that use several forest types. Because it is at home along rivers, waterways are less of a barrier to it than to other primates in the region.

Allen's swamp monkey vs guenons

For most of its history the swamp monkey was lumped with the guenons, and it still looks like one at a glance. Its body plan and social life mix guenon and baboon traits.

Conservation status

Allen's swamp monkey is listed as Least Concern on the IUCN Red List and is on Appendix II of CITES. It is still expected to come under pressure.

The main threat is unsustainable hunting for bushmeat, both for local food and for commercial sale. Logging in the Congo Basin is driving new road networks close to its habitat, which makes populations easier for hunters to reach. Some monkeys may also be captured for the exotic pet trade.