Tana river mangabeys are commonly preyed upon by African rock pythons. Other predators may include African crowned eagles, martial eagles, and Nile crocodiles (Wieczkowski and Butynski 2007). Tana river mangabeys use group signaling to alert other members of the group to predators.
Known Predators:
Tana rirver mangabeys are medium-sized mangabeys of the genus Cercocebus. They exhibit a pale-grey/brown coloration, and have a conspicuous crest on their crown and white eyelids (Medley 1993). Their body is covered in wavy hair with inconspicuous dark bands, and their forearms and hands are darker in color than their tail and upper limbs (Groves 1978). Their face is jet black with strongly contrasting white eyebrows, distinguishing it from C. torquatus and C. agilis.
Males and females are similiar in color though different in size. The tail is approximately 33% longer in males (Groves 1978). Males average 9.46 kg in mass with a head-and-body length from 49 to 63 cm and a tail length averaging 68 cm. Females weigh an average of 5.4 kg, with a head-and-body length from 44 to 53 cm and a tail length averaging 50 cm ("Tana River Mangabey (Cercocebus galeritus)" 2010).
Males have the smallest skulls in the genus Cercocebus (Groves 1978). A distinguishing crest on their crown is made up of long (10 cm) darkish brown/grey hairs, parted down the middle. Infants have pink faces, ears, and limbs, and lack the crown (Wieczkowski and Butynski 2007).
The dentition of Tana river mangabeys is uniquely adapted to a hard-item diet. Their thick molar enamel is able to withstand crushing forces, their large maxillary and mandibular fourth premolars provides increased seed-crushing surface area, and their shortened snout allows for a more powerful bite (Wieczkowski 2009).
Average mass: Males 9.46 kg; Females 5.4 kg.
Range length: 44 to 63 cm.
Average length: Males 56 cm; Females 48.5 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Little information is available regarding the lifespan of Tana river mangabeys, as few are raised in captivity and few long-term field studies have been carried out on large populations, which are limited by the small total population size of this species. Nonetheless, given what is known of other members of this genus and extrapolations from field observations, longevity has been estimated at 19 years (Wieczkowski and Butynski 2007).
Average lifespan
Status: wild: 19 years.
Tana river mangabeys are largely terrestrial and live in floodplain forests along the lower Tana river. These forests are dependent on the height of the groundwater table and the Tana river's processes of flooding, erosion, and nutrient recharge. Tana river mangabeys inhabit 27 of the 60 riparian forests along the river, inhabiting a total area of only 26 sq km. These forests are naturally fragmented due to the meandering course of the river (Wieczkowski and Kinnaird 2008).
Abundance of Tana river mangabeys is correlated with forest fragment area as well as density of trees (Weiczkowski 2004). Tana river mangabeys, though semi-terrestrial, are forest-dependent, as much of their diet is composed of plant material from the canopy or sub-canopy. On average Tana river mangabeys spend 56% of their time on the ground, 32% in vegetation up to 10 m, and 12% of their time above 10 m. Because of recent habitat fragmentation, Tana river mangabeys have been observed traveling through non-forest matrix in search of food (Weiczkowski 2010). This demonstrates their flexibility in ranging behavior, specifically their ability to increase home range size.
Four tree species account for approximately half of all trees found in this low elevation area: Phoenix reclinata, Polysphaeria multiflora, Garcinia livingstonei, and Sorindea madagascarienses. In general, however, the Tana River floodplain supports many endemic plant and animal populations with small distributions, and the area thus has high biodiversity (Butynski and Mwangi 1994).
The Tana river is a highly seasonal environment, with the most rainfall occurring from March to June and November to December. The hottest months in this region are between October and June (Medley 1993).
Tana river mangabeys tend to choose tall trees with full crowns and poor accessibility to non-arboreal species for sleeping sites. Predator avoidance, afternoon feeding area, and group ranging patterns also influences sleeping site choice. Tana river mangabeys prefer to sleep in the forks of branches near the main trunk of the tree.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: forest
Other Habitat Features: riparian
Communication among Tana river mangabeys is complex and crucial for establishing dominance and maintaining group cohesion. Visual communication predominates, and mating and competitive displays are common. Females display their receptivity to mates with large, monthly estrous swellings (Wieczkowski and Butynski 2007). They also exhibit a post-conception swelling that lasts 8 to 9 days after 2 months of pregnancy (Kinnaird 1990). Unlike other species of mangabeys, males do not head bob, swagger, or tongue-flick while courting or at other times (Wieczkowski and Butynski 2007).
Vocalizations are also common among Tana river mangabeys. Females tend to vocalize shortly following copulation (Gust 1994). Males often emit a loud "whoop-gobble," which is audible over 1 km away and lasts over 90 seconds on average. This generally is emitted in the morning hours and is used to assert dominance and to aid in intergroup spacing. This auditory communication between groups minimizes aggressive intergroup competition (Gust 1994).
During a male-male confrontation, agonistic behaviors include lunges, chases, and branch shaking. They also flash their eyelids to assert dominance, which is notable given the impressive contrast between their white eyelids and black face (Wieczkowski and Butynski 2007).
As with most other primates, the importance of olfaction has been reduced in this species.
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Tana river mangabeys are endangered and, with only 1,000 to 1,200 individuals remaining in the wild, they are ranked as one of the world's 25 most threatened primates in 2002 (Wieczkowski and Butyski 2007). Their numbers continue to decrease.
The greatest threat to Tana river mangabeys is habitat degradation through unsustainable forest clearing and resource extraction (Butynski and Mwangi 1994). Between 1994 and 2000, approximately 30% of the forest within their range was cleared for agriculture (Wieczkowski 2005). Decimation of the favored food source of Tana river mangabeys, the palm species Phoenix reclinata, has only exacerbated the general habitat degradation.
The Tana River Primate National Reserve, created in 1976, has helped stem the habitat degradation, however only 56% of mangabey groups are located in this preserve. Additionally, the preserve was degazzetted in 2007, and currently none of the habitat of Tana river mangabeys is legally protected (Wieczkowski and Butynski 2007).
The lower Tana River contains an abundant wealth of biodiversity, and its conservation is seen as one of East Africa's most serious and challenging biodiversity conservation problems (Butynski and Mwangi 1994). Tana river red colobus (Colobus badius *rufomitratus), are also endemic to the lower Tana River and are endangered (Butynski and Mwangi 1994).
US Federal List: endangered
CITES: appendix i
IUCN Red List of Threatened Species: endangered
There are no known adverse affects of Tana river mangabeys on humans.
However, humans have attempted to utilize much of the forests surrounding the Tana River as farmland, encroaching on the little remaining habitat of this species. In this way, the conservation of Tana river mangabeys has adversely affected development and agricultural expansion in the lower Tana River region of Kenya (Wieczkowski and Butynski 2007).
Tana river mangabeys are of tremendous research and educational importance. Given their limited distribution, they are well studied, and research of their ecosystem dynamics has proven enlightening (Homewood 1978; Wieczkowski and Butynski 2007). Tana river mangabeys have also become a popular face for the conservation of the lower Tana River, which contains an astounding variety of species, many of which, including Tana river mangabeys and Tana river red colobus, are not found anywhere else in the world (Butynski and Mwangi 1994).
Positive Impacts: research and education
Tana river mangabeys play an important role in seed distribution, as roughly one-third of their diet is comprised of nuts and seeds. They also serve as host for a variety of gastrointestinal parasites. Ten species of nematodes (including Ascaridia galli, Synodontis fuelleborni, and Trichuris trichiura) and three species of protozoans (Escherichia coli, Entamoeba histolytica, Entamoeba hartmanni) have been found in fecal samples (Mbora and Munene 2006). Tana river mangabeys display a high diversity of gastrointestinal parasites because of the fragmentation and diversity of their habitat combined with their large home ranges (Mbora and Munene 2006). Further study is necessary to determine the effects of this parasite load, as parasites and their associated infectious diseases are a major threat to the conservation of endangered species (Mbora and Munene 2006).
Ecosystem Impact: disperses seeds
Commensal/Parasitic Species:
Tana river mangabeys feed primarily on fruits and seeds. Contrary to early descriptions of the species, they do not specialize on ripe fruits, but rather exhibit considerable flexibility in their dietary selection, both spatially and temporally (Wieczkowski 2005; Homewood 1978). This flexibility has allowed them to best exploit their fragmented riparian habitat at all times of the year and has aided their response to anthropogenic habitat change.
Tana river mangabeys increase their home range in times of food scarcity, often shuttling between forest patches through grassy matrix (Wieczkoski 2010). On average, they spend 58% of their waking hours foraging and feeding (Wieczkowski and Butynski 2007).
Tana river mangabeys eat plant materials that are most abundant, including ripe fruit, ripe seeds, unripe fruit, and unripe seeds (Wieczkowski 2005). Their average annual diet is composed of 44% fruit and 32% seeds, with stems, leaves, insects, and fungi making up the remaining 24% (Kinnaird 1990). Food availability is highest from November to April.
Members of this species have been observed feeding on 96 different species of plants, though eight of these comprise over 80% of their diet: Aporrhiza paniculata, Acacia robusta, Diospyros mespiliformes, Ficus sycamorus, Hyphaenae compressa, Pachystela msolo, Pachystela reclinata, and Saba comorensis (Homewood 1978; Wieczkowski 2004).
Tana river mangabeys have unique dental adaptations specialized for accessing unripe fruit and hard nuts and seeds. Their large incisors delay wear from gouging fruits. They also have thick molar enamel, able to withstand crushing forces, and enlarged fourth mandibular and maxillary premolars, providing increased surface area for crushing seeds (Wieczkowski 2009).
Animal Foods: insects
Plant Foods: wood, bark, or stems; seeds, grains, and nuts; fruit
Other Foods: fungus
Primary Diet: herbivore (Frugivore , Granivore )
Tana river mangabeys, Cercocebus galeritus, are endemic to a fragmented forest mosaic along 60 km of the lower Tana River in southeast Kenya between Kanjonja to the north and Garsa to the south (Medley 1993). Their entire population is confined to roughly 34 of the 60 riverine forests supported by the river. These 34 inhabited forests cover approximately 26 sq km (Butynski and Mwangi, 1994).
Biogeographic Regions: ethiopian (Native )
Tana river mangabeys live in multi-female social groups averaging 27 animals. Groups are generally composed of 2 adult males, 7 adult females, 2 subadult males, 2 subadult females, 10 juveniles, and 4 infants (Wieczkowski and Butynski 2007). The species exhibits a polygynous mating system; the dominant male mates with many estrous females (Kinnaird 1990).
Agonistic behaviors demonstrated in competing males include eyelid flashes, lunges, chases, grabs, bites, branch shaking, and vocalizations (Gust 1994). Males also emit a loud "whoop-gooble" call that can be heard for nearly a kilometer, which in part is used to assert and maintain dominance (Wieczkowski and Butynski 2007). Mean duration of the gobble is 90.5 seconds, with most calls occurring in the morning hours between 0630 and 1100 h.
Females exhibit large, monthly estrous swellings that last 4 to 5 days and signal receptivity to copulation (Wieczkowski and Butynski 2007). Amicable behavior demonstrated between courting couples includes stylized presentations, grooming, and play (Gust 1994). Males exhibit a unique pattern of mounting during copulatory behavior. The male grasps the female's ankles with his feet and places his hands on her hips. After copulation, the female darts away from the male (Gust 1994).
Mating System: polygynous
Female Tana river mangabeys exhibit large, monthly estrous swellings that last 4 to 5 days and signal receptiveness to copulation (Wieczkowski and Butynski 2007). After a gestation period of 180 days, females give birth to a single offspring (Kinnaird 1990). Twins have never been observed in the wild (Kinnaird 1990). During parturition, other individuals in the group do not stand within 5 m of the birthing female. Females in the group may approach the female and her newborn approximately 20 min after birth (Kinnaird 1990).
Copulation and births are largely timed to coincide with greatest food availability. Thus, births tend to peak between August and April, a time of high food availability. Female Tana river mangabeys give birth once every 18 to 24 months, and about 63% of females in a group give birth during a given year (Kinnaird 1990).
Growth is likely similiar to that of other species in the genus Cercocebus. Females likely reach sexual maturity at 3 years of age and breed for the first time at 6.5 years of age. Males reach sexual maturity slightly later, at around 5 years of age, and successful males breed soon thereafter, often by the age of 7 (Wieczkowski and Butynski 2007).
Breeding interval: Female Tana river mangabeys give birth to a single offspring once every 18 to 24 months.
Breeding season: Based on birthing peaks, mating of Tana river mangabeys likely peaks between February and October.
Average number of offspring: 1.
Average gestation period: 180 days.
Average age at sexual or reproductive maturity (female): 3.5 years.
Average age at sexual or reproductive maturity (male): 5 years.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Female Tana river mangabeys exhibit post-conception swellings 2 months after fertilization (Kinnaird 1990). This has also also been observed in chimpanzees, gorillas, red colobus, and rhesus macaques, and likely functions to confuse paternity, thereby encouraging male investment in the young.
With dominance reversal among males, or when a new male enters and takes over a group, the newly dominant male may practice infanticide (Kinnaird 1990). Females protect their infants from the new alpha male during dominance changes (Gust 1994).
Not much is known about provisioning post-weaning, though females likely provide the most care (Gust 1994). Although both males and females display interest in newborn infants, only juvenile and adult females demonstrate sustained interest, suggesting further maternal behavior (Kinnaird 1990).
Parental Investment: female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
The Tana River mangabey (Cercocebus galeritus) is a highly endangered species of primate in the family Cercopithecidae. Some authorities have included the taxa agilis and sanjei as subspecies of this species,[4] while others award these full species status.[1]
It is endemic to riverine forest patches along the lower Tana River in southeastern Kenya. It is threatened by habitat loss and degradation, which has increased in recent years.[5] This species was, together with the equally endangered Tana River red colobus, the main reason for the creation of the Tana River Primate Reserve in 1978,[6] but human encroachment within this reserve continues.[7] Recently, it has been suggested that 20,000 hectares of the Tana River Delta should be transformed into sugarcane plantations, but this has, temporarily at least, been stopped by the High Court of Kenya.[8]
The Tana River mangabey is a medium-sized primate with a long semiprehensile tail, a yellow-brown coat, and a center part on the crown of the head with long, dark fur. The species has white eyelids that contrast to its darker face like other Cercocebus species. This contrast in the eyelids is believed to be used as part of the species' complex communication system.[9] The species also has specialized dental morphology for feeding on hard nuts, seeds, and fruits.
The Tana River mangabey is diurnal and semiterrestrial. It spends most of its time on the ground, but is still considered arboreal due to its sleeping area. The species sleeps in trees about 27-37 m in height, which have a sparse canopy cover of 25–60%. The primate sleeps in the forks of the branches of these trees or near the main trunk. It is believed to sleep in trees to reduce the risk of predation and chooses this site according to its last feeding position in the area.[10]
Group size ranges from 13–36 individuals, and sometimes combining to form aggregations of 50 to 60 individuals.[11] These groups consist of multiple males and multiple females. The species has an average day-range length of 1.25 km.[12] During the dry season when food is limited, groups maintain discrete territories with minimal overlapping. To maintain these territories, males give spatial vocalizations and territorial displays at fixed boundaries. The males within the group may also engage in active combat with outside group leaders invading the territory. In the wet season when food is abundant, boundaries are broken down. Foraging ranges for different groups extend, and considerable overlap occurs between the different groups. During this time, groups are more tolerant of one another and meet and intermingle.[13] The Tana River mangabey has a few predators, such as the Central African rock python, crowned eagle, martial eagle, and Nile crocodile.
The Tana River mangabey is a polygynous species with two or more males within each group depending on the size of the group. The average adult male weighs about 10.2 kg, while the average adult female weighs 5.5 kg, thus exhibiting size sexual dimorphism within the species.[12]
The female gives birth to a single offspring after a gestation period around 170–180 days. During the first two months after birth, the infant is guarded by its mother and begins to develop a close bond. In the third month, the infant begins socializing with other infants and adult group members, but remains in close proximity to its dam. The females within the group usually have lasting bonds with their mothers, while the males become more independent and spend more time away from the group or on the periphery. If a group loses one of its males, another male may be recruited from peripheral solitary males to maintain the structure of the group.[13]
The species is omnivorous, feeding on leaves, seeds, fruits, insects, and reptile and bird eggs. An opportunistic feeder, it is semiterrestrial, where it may rummage through the leaf litter for food. The mangabey gets most of its food from subcanopy and canopy trees, although it spends most of its time feeding and moving on the ground. It consumes the fruit and seed from about 50 different tree species. Feeding is performed 48% of the day, while sleeping accounts for 15%, and resting accounts for 14% of the day.[12] The species' annual diet consists of 46.5% seeds and 25.6% fruit consumption.[14] Critical food resources for the species are Ficus sycomorus, which fruits year-round, and Phoenix reclinata, which is also a primary food species and fruits when others do not.[15]
The Tana River mangabey has dental morphology well suited for the food type it consumes. The species has large incisors for the tearing of the tough skin on the fruits it eats. Its large maxillary and mandibular fourth premolars have increased surface area to crush seeds, and its shortened face increases bite force.[16]
The Tana River mangabey is found in the southeastern portion of Kenya along the Tana River, within 27 forest fragments along a 60 km stretch of floodplain forests. The gallery forest along the Tana River is home to several primate species - the Tana River mangabey, Tana River red colobus, blue monkey, yellow baboon, vervet monkey, and two species of bush babies.[17] This species is restricted to riverine gallery forests in this area.[18] The forests in which it is found are naturally fragmented due to the meandering of the Tana River and its fluctuating water levels. The forest is becoming even more fragmented due to habitat loss from human disturbance, which may reduce species' survival.
One of the greatest threats to endangered species is habitat loss. This is also the case with the Tana River mangabey. An estimated 50% of the original forest has been lost in the last 20 years. The Tana River area is losing its forests to agriculture.[9] Felling of canopy trees for canoe construction, wild honey collection, and palm fronds are being used for thatching and mats. Subcanopy trees are being used for housing poles and the topping of Phoenix reclinata for palm wine collection severely impacts the resources used by the species.[19] Tana River mangabeys are also hunted and trapped in response to local crop damage. This trapping may occur and appears to be occurring at low levels within the forests.
The Tana River mangabey is listed as one of The World's 25 Most Endangered Primates. A 1994 census estimated the species' population to be 1,000 to 1,200 individuals.[19] It was listed under the U.S. Endangered Species Act as being endangered in 1970. The species is also listed as critically endangered under the International Union for Conservation of Nature and under CITES is listed under Appendix I. This species is listed on Class A of the African Convention on the Conservation of Nature and Natural Resources.
The Tana River Primate Reserve was established in 1976 to protect the remaining forest along the Tana River and the endemic Tana River mangabey. The reserve protects an area around 171 km2 with two areas of 9.5 and 17.5 km2 being forested. The reserve contains about 56% of the Tana River mangabey groups, with about 44% living in forests outside of the reserve. About 10% of the groups living in forests outside of the reserve are under the management of the Tana Delta Irrigation Project.
The objective of the Tana River Primate Reserve was to conserve the biodiversity within the Tana River area and protect the endangered Tana River mangabey. The conservation of this species is a high priority for primate conservation in Kenya. In 2007, the High Court in Kenya ruled the reserve was not abiding by the laws. This led to the forested areas that the mangabey inhabited losing their legal protection.[20] With the poor management of the Tana Delta Irrigation Project, habitat loss outside the reserve also continues. The Tana and Athi Rivers Development Authority, which is in charge of the project, are now in the process of expanding to establish a sugarcane plantation, which will in turn remove more forested areas.
A five-year project in 1996 with the Kenya Wildlife Service and Kenya Forest Department was funded by the World Bank/Global Environment Facility. The project's goals were to enhance conservation and protection of these primates and forests. The project was poorly managed and was terminated after two years, leaving the wildlife service with the protection of these areas.
The Ishaqbin Conservancy is a community initiative in the Tana River Primate Reserve. Here, communities are working with Kenya Wildlife Service to develop tourism side-by-side with conservation. Tourism development is believed to be important in that it will secure the conservation of the habitat and the species with the communities around the reserve. Tourism will benefit both the mangabey and local communities through economic development and a reduction in habitat loss. The conservancy will also help to form a buffer around the reserve, which will help to reduce human impact inside the reserve.[21]
{{cite journal}}: Cite journal requires |journal= (help) The Tana River mangabey (Cercocebus galeritus) is a highly endangered species of primate in the family Cercopithecidae. Some authorities have included the taxa agilis and sanjei as subspecies of this species, while others award these full species status.
It is endemic to riverine forest patches along the lower Tana River in southeastern Kenya. It is threatened by habitat loss and degradation, which has increased in recent years. This species was, together with the equally endangered Tana River red colobus, the main reason for the creation of the Tana River Primate Reserve in 1978, but human encroachment within this reserve continues. Recently, it has been suggested that 20,000 hectares of the Tana River Delta should be transformed into sugarcane plantations, but this has, temporarily at least, been stopped by the High Court of Kenya.
