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). (Butynski and Mwangi, 1994; Medley, 1993)
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). (Butynski and Mwangi, 1994; Medley, 1993; Wieczkowski and Kinnaird, 2008; Wieczkowski, 2004; Wieczkowski, 2010)
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. (Wahunga, 2001)
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). ("Tana River Mangabey (Cercocebus galeritus)", 2010; Groves, 1978; Medley, 1993; Wieczkowski and Butynski, 2007; Wieczkowski, 2009)
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). (Gust, 1994; Kinnaird, 1990; Wieczkowski and Butynski, 2007)
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). (Kinnaird, 1990; Wieczkowski and Butynski, 2007)
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). (Gust, 1994; Kinnaird, 1990)
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). (Wieczkowski and Butynski, 2007)
Tana river mangabeys are highly social, diurnal animals. They are semi-terrestrial, spending about 56% of their time on the ground (Wieczkowski and Butynski 2007). This time is largely spent foraging for food, and foraging activity peaks around mid-day (Kinnaird 1990). Tana river mangabeys spend more time foraging and moving when food is scarce and more time on social behaviors when food is abundant (Wieczkowski and Butyski 2007).
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). A single alpha male is typically dominant, though occasionally a beta male is tolerated. Dominant, agonistic displays include eyelid flashing, chases, branch shaking, and vocalizations. In numerous long-term studies, limited aggressive, damaging behavior has been observed (Gust 1994). Amicable behavior demonstrated between courting couples includes stylized presentations, grooming, and play (Gust, 1994).
Territoriality varies temporally. When fruit and seeds are scarce, groups use non-overlapping areas of their home ranges to avoid confrontation. The loud, permeating "whoop-gobble" of adult males, audible at over 1 km, aids in inter-group spacing. When fruit is abundant and uniformly available, groups have been observed moving and feeding together in the wild. However, when food is patchy, scarce, and defendable, territoriality and confrontation have been exhibited. Often, two groups approach each other, but aggressive encounters rarely ensue (Kinnaird 1990). Groups of Tana river mangabeys have been known to come together in bands during the rainy season, possibly as a means to avoid in-breeding during a periods of increased conception (Groves 1978).
Curiously, sleeping site choice in one group of Tana River mangabeys demonstrated overlap with that of yellow baboons, though never simultaneously (Wahunga 2001). During and after heavy rainfall, these two species also demonstrated dietary overlap, and both remained in the forest, corresponding to increased fruit availability (Wahunga 1998). Tana river mangabeys do not form polyspecific associations with other species of primates (Wieczkowski and Butynski 2007). (Groves, 1978; Gust, 1994; Homewood, 1978; Kinnaird, 1990; Wahunga, 2001; Wahungu, 1998; Wieczkowski and Butynski, 2007)
Home range size of Tana river mangabeys ranges from 0.17 to 1.01 sq km (average 0.46 sq km). However, home range size increases with group size and decreases with improved habitat quality, specifically forest density (Wieczkowski 2005). Ranging behavior varies, typically in order to maximize resource acquisition. Tana river mangabeys also increase their home range in response to low per capita density of food trees (Wieczkowski 2005). This flexibility has permitted survival in increasingly degraded and fragmented habitats. Tana river mangabeys are also adept at moving through brush matrix of Acacia between forest patches, allowing them to reach new, neighboring forest patches if necessary (Wieczkowski 2010).
Home range overlap with neighboring groups generally varies between 25% and 36%. Some small groups with smaller home ranges, however, share a single home range. Over the course of a day, groups range an average of 1.511 km in search of food and suitable sleeping sites (Wieczkowski and Butynski 2007). (Wieczkowski and Butynski, 2007; Wieczkowski, 2005; Wieczkowski, 2010)
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).
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). (Homewood, 1978; Wieczkowski and Butynski, 2007; Wieczkowski, 2004; Wieczkowski, 2005; Wieczkowski, 2009; Wieczkowski, 2010)
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. (Wieczkowski and Butynski, 2007)
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). (Butynski and Mwangi, 1994; Mbora and Munene, 2006)
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). (Butynski and Mwangi, 1994; Homewood, 1978; Wieczkowski and Butynski, 2007)
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). (Wieczkowski and Butynski, 2007)
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). (Butynski and Mwangi, 1994; Butynski, et al., 2008; Wieczkowski and Butynski, 2007; Wieczkowski, 2005)
Gregory Mittl (author), Yale University, Eric Sargis (editor), Yale University, Gail McCormick (editor), Animal Diversity Web Staff.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
uses sound to communicate
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
having more than one female as a mate at one time
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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