Tana River Mangabey

Name and Classification

Wilhelm Peters described this monkey in 1879. His type specimen came from Mitole, near the Tana River mouth. Today it sits in the genus Cercocebus, the white-eyelid mangabeys.

Local Pokomo guides call it Garau.^[3] Older papers call it the Tana River crested mangabey.

Its relatives were long lumped into one species. The agile mangabey and golden-bellied mangabey were once its subspecies. So was the Sanje mangabey of Tanzania. Major references now rank all four as species, but debate continues.^[4]

In 1974, Colin Groves questioned that grouping. To him, the agile mangabey was no closer kin. The collared mangabey and sooty mangabey were just as close.

A 2026 genetic study links it with agile, golden-bellied and Sanje mangabeys. Tana, agile and Sanje loud calls once seemed indistinguishable.

Physical Description

A 1974 field report describes a yellowish monkey with a light underside. Its black face contrasts with the fur. Hair parts on the front of the crown. Long hairs then sweep out over the forehead.

Another observer called its fur fawn-gray.^[5] It was described as large and slender, with a semi-prehensile tail. That fur places it among the yellow monkeys. Its fawn-gray tones also fit the gray monkeys.

It has white eyelids and a backswept crest. Its face is dark gray to black.

The Berlin type adds detail.^[6] Long, blackish brown crown hairs fall over the ears. The throat and underparts are yellowish white. The hands and feet are blackish brown.

An adult male can look like a baboon at first. A female or young one can pass for a vervet monkey. The parting on the crown gives it away.

Size and Weight

Measurements of live Tana mangabeys are not published on open sources. Elliot listed measurements of the mounted type in Berlin. Its total length was 1,350 mm (53 in). The tail made up 730 mm (29 in). That leaves a head and body of about 62 cm (24 in). The sex of the type is not stated.

One study says it matches the Tana River red colobus in size.^[7] No reliable weights for this species appear in open sources.

Similar Species Compared

The agile mangabey lives in Central African forests.^[8] Its range covers Cameroon, Gabon, both Congos and the Central African Republic. Its type skin is pale reddish brown, with yellow-tipped hairs. It eats fruit, seeds and shoots, and sometimes infant duikers. At Mondika, groups averaged 21 animals. The IUCN lists it as Least Concern.

The Sanje mangabey lives in Tanzania's Udzungwa Mountains.^[9] It was first described in 1981, without a formal name.^[10] Its face is nearly cream, unlike the Tana mangabey's dark face. Its coat is intermediate between the Tana and agile mangabeys. It lives in submontane and montane forest, up to 2,000 m. The IUCN lists it as Endangered.

The Tana River red colobus shares the same river forests.^[11] It is gray with a red cap. It is a leaf eater and rarely comes to the ground. Both monkeys are Critically Endangered.

Range and Distribution

It is found only in Kenya. It lives along a 60-km stretch of the lower Tana River. Its range runs north to Nkanjonja and south to Hewani. A small number may live in the Tana Delta.

It lives in about 27 small forests, some of them isolated. They range from 1 to 500 ha (2.5 to 1,240 acres). In 1994, it occupied less than 26 square km (10 sq mi). Their elevation is 20 to 40 m (66 to 131 ft).

A 2024 action plan reports a few groups in the Tana Delta.^[12]

Habitat Needs

It lives in flood-plain forest and riverine gallery forest. It also uses nearby woodland and bushland. These forests grow in a dry region.

They depend on river floods and groundwater, not rain.^[13] Most grow within about 1 km (0.6 mi) of the river. Across 38 months, annual rainfall averaged 582 mm (23 in).

Forest size and tree density best predicted its numbers.^[14] Inside the reserve, the main food trees also mattered.

Diet and Feeding

The IUCN calls it frugivorous. It feeds mostly on the ground and up to 2 m high. That fruit-based diet makes it one of the frugivorous monkeys.

Seeds topped the diet of one group in 2000 and 2001. Seeds made up 46.5% of the year's feeding. Fruit made up 25.6%. Insects and snails made up 10.9%. New stems added 7.6%, and leaves only 3.8%. The animal food also counts it among the omnivorous monkeys.

The wild date palm is a key food.^[15] It can supply up to 62% of the monthly diet. Mangabeys rely on its fruits and seeds when other fruit is scarce. People also harvest every part of this palm.

The seeds it eats are very hard.^[16] Their mean crushing resistance was 12.8 kg. That beats seeds eaten by other hard-object feeders.

Two groups were followed for 13 months in the 1970s.^[17] When food grew scarce, they ate a wider mix of foods. They also searched more ground and moved farther.

Its forest changed over 13 years.^[18] By 2000, its diet species had shifted from 1988.

Behavior and Groups

It is semi-terrestrial. It is at home high in trees or on the ground. Groups average about 27 animals, with a range of 6 to 62.

Groups held 13 to 36 animals in the 1970s. Most had more than one adult male. Extra males lived alone near the groups.

In the dry season, groups defended territories. Adult males used loud spacing calls and displays. In the rains, groups could mix into crowds of 40 to 50.

Two groups showed flexible defense.^[19] They avoided each other when fruit was scarce. They mixed peacefully when fruit was plentiful and spread out. They fought when rich fruit was clumped in one spot.

The adult male loud call is called the whoop-gobble. A 1974 report described deep grunting booms, then hoarse screeches. Groups often traded these calls at dawn.

One group's yearly range nearly tripled.^[20] It used 17.25 ha (43 acres) in 1974. It used 46.75 ha (116 acres) in 2000 and 2001. Its size went from 36 to 17, then to 50 animals.

It can cross up to 1 km of nonforest matrix between forests.^[21] One group averaged 100 minutes in one matrix area. It spent most of that time eating.

In 2004, a study group split into two.^[22] It was the first reported group fission in Cercocebus.

It shares sleeping trees with the yellow baboon.^[23] The two species never used a site at the same time. On forest edges, it also meets the vervet monkey.

Breeding and Young

Seven wild females were followed through pregnancy.^[24] Gestation averaged 180 days. All showed sexual swellings after the first two months of pregnancy.

A mother guards her infant closely for two months. In the third month, it plays more with peers.

A 2018 dissertation summarizes earlier birth data.^[25] It reports year-round breeding with a peak from October to February. Its listed predators are crowned eagles, rock pythons, leopards and yellow baboons.

Population and Status

Estimates have swung over the decades. A 1972 survey estimated about 2,245, but called it unreliable. Homewood estimated 1,000 to 1,500 in 1975.

Between 1975 and 1985, numbers fell an estimated 45%.^[26] The action plan gives a 1994 estimate of 1,000 to 1,200.

A 2001 census of 73 forest patches counted 2,070.^[27] They lived in 59 groups. About 56% of groups lived inside the reserve.

No full census has been published since. The 2019 Red List assessment estimated about 1,000. The trend was downward. The 2024 action plan says it may now number below 1,000.

The 2024 action plan puts its effective population size below 100. Yet it keeps high genetic diversity.^[28] Females stay in the groups where they were born.

The IUCN listed it as Endangered in 2008. It was moved to Critically Endangered in 2019. Assessors predict a fall of over 80% within 33 years. That is especially likely if the reserve is annulled.

Major Threats

Its forests keep shrinking. One study tracked 21 years of forest loss up to 2001.^[29] Forest area fell by 34.5% in that time. Loss was 38% outside the reserve and 29.2% inside.

People clear forest for farms. Fires, livestock and wood cutting damage the patches. Fig trees are felled to make canoes. People also harvest its key food, the wild date palm.

Dams change the river itself. Five hydroelectric dams upriver have altered flows and floods. That alters the water table and floods the forests need. The Red List described a sixth dam as under construction. Large irrigation schemes would come with it.

Some farmers kill it as a crop pest. Insecurity and inter-ethnic violence make protection harder.

Groups in disturbed forest fared worse.^[30] They were smaller and traveled farther each day. They also had larger home ranges and lower fecundity.

Conservation Efforts

Kenya created the Tana River Primate National Reserve in 1976. It covers about 169 square km (65 sq mi). The 2019 assessment put about 56% of the mangabeys inside it.

In January 2007, the High Court of Kenya ordered the reserve annulled. Kenya's 2013 wildlife law sets the rules for that step.^[31] The Cabinet Secretary must publish the notice. Parliament must approve the proposal. The 2024 action plan says it has not happened.

The same law lists it as Critically Endangered in Kenya. It is on CITES Appendix I.

The Ndera Community Conservancy was set up in 2010. It aims to protect forest along the lower Tana. The Tana Delta became a Ramsar Site in 2012.

It was among the 25 most endangered primates for 2002 to 2004. The action plan calls for a full census and forest restoration. It also calls for restoring the Mchelelo research camp.

Explore more monkeys starting with T. Or browse all types of monkeys.

Common Questions