Piliocolobus rufomitratus is limited to a small range of forest along the lower Tana River in Eastern Kenya. The Tana River runs from the eastern Kenyan Highlands into the Indian Ocean. Its range includes the Tana River National Primate Reserve outside the city of Wenje. (Medley, 1993)
Piliocolobus rufomitratus, or Tana River red colobus monkey, inhabits patches of evergreen riverine forest that undergo periodic flooding from the Tana River. These isolated clumps of forest are under the influence of groundwater fluctuation, river course changes and human disturbance which result in a very fragmented and unstable habitat only further endangered by human encroachment (Decker & Kinnaird, 1992). This riverine forest habitat experiences an average annual precipitation of 470 mm and temperatures ranging between 21.4°C and 33°C (Medley, 1993). In contrast to the habitat of the other red colobus species across East and Central Africa, this habitat is more arid and has a lower density and diversity of tree flora (Marsh, 1981a). In general, the canopy of the Tana River forest is more open than the habitat at other red colobus sites (Oates, 1994). (Decker and Kinnaird, 1992; Marsh, 1981a; Medley, 1993; Oates, 1994)
The pelage of P. rufomitratus is ruddy black on the dorsal side and red with brown on the chest, inner portions of the limbs and head (Nowak, 1999). Head and body length ranges between 450 and 670 mm. The tail is gray and fairly long, measuring 520 mm to 800 mm. This species exhibits several traits that may be adaptations to an arboreal lifestyle, including long, slender digits and the loss of the thumb tubercle, common in all colobine monkeys. The hind limbs are well developed for leaping across the canopy and may be particularly long. Though no definitive study on mass has been completed, weights may range between 5.1 and 11.3 kg like other red colobus species. A closer estimate may put their mean weight at 5.8 kg, near that of the more isolated West African species of the Procolobus kirki (Oates, 1994). (Nowak, 1999; Oates, 1994)
The mating system in this species is generally polygynous, especially when only one male is present. Often the dominance hierarchy determines who is allowed mating access, and in the peculiar case of Tana River red colobus monkeys, there is frequently a single male or a small group of males that prohibits extra-group males from mating or even entering the group. (Newton and Dunbar, 1994; Marsh, 1979) (Marsh, 1979; Newton and Dunbar, 1994)
Very little is known about the reproductive cycle of these primates in the wild. They are difficult to find and track due to their constant migration.
Unlike most colobine monkeys, red colobus females exhibit periodic swelling of perineal tissue throughout the year (Nowak, 1999; Oates, 1994). These swellings often coincide with an increase in copulation, so it is assumed that they mark the time of ovulation, though false swellings (those not correlated with ovulation) have been seen in other primates and may serve as a possible defense against infanticide. There appears to be no distinct birthing season though studies to determine relative birth spacing are lacking (Marsh, 1979).
Typically the dominant male mates with the females in his social group. Copulations are initiated by females who perform courtship displays and present themselves to the male. Before mating, there are frequent copulation calls serving to draw males into the area. During mating, the females may give other calls that continue to attract males (Struhsaker, 1975; Oates, 1994). Harassment during copulation by non-mating males was frequent in the rain-forest species (Struhsaker, 1975); however, there are significantly fewer males in Tana River red colobus groups (often only one or two males) so the impact of this harassment is probably negligible (Marsh, 1979). There has not been a definitive study on the impact of the smaller group size, lower male numbers and reduced habitat on the reproduction of Tana River red colobus monkeys, and this could be an interesting research opportunity. (Marsh, 1979; Nowak, 1999; Oates, 1994; Struhsaker, 1975)
In general, red colobus monkeys breed throughout the year. Estimated gestation is 4.5 to 5.5 months, with an estimated interbirth interval of 26 months. The exact period of nursing has not been reported for these animals, however, we may infer that weaning probably occurs before the infant is 20 months old, as continued nursing might inhibit conception of another offspring. (Nowak, 1999; Nowak, 1999)
At birth the infant’s pelage is silky black on the back with a gray underbelly, helping to distinguish infants from older monkeys. Pink flesh is exposed on the muzzles, ears, palms and soles for 3 to 4 weeks (Oates, 1994). The fur remains gray until 2 to 2.5 months of age, when the head begins to turn reddish on the crown.
After birth, infants cling to their mothers' underbelly and remain dependent on her. In general infants stay very close to the mother until 2 to 3.5 months of age, traveling only about 1 meter from her during this this time. By 3.5 to 5.5 months they typically engage in play with other monkeys (Marsh, 1979). NAround 18 months of age, young females of the group emigrate to another group and may continue to move from group to group throughout their lifetime, as female membership is very fluid. Some males may leave the group during adolescence but it is difficult to become accepted into another group in this patrilineal social structure (Struhsaker, 1975).
Often only the mother grooms and carries the infant and infant handling, allomothering or aunting (handling/care of the infants by non-mothers) are not common behaviors. This is most likely because the patrilineal distribution pattern in which females emigrate from their natal group results in low levels of relatedness between females in the same group. Unrelated females are much less likely to allow their infants to be handled by other females. This is unlike the pattern seen in baboons, in which the females are more closely related to one another (Newton and Dunbar, 1994).
Males contribute very little to the offspring other than proximal protection from predation and resource allocation. There doesn’t seem to be any relationship between the dominance hierarchy of males and the infants present in the group. However, there are reports of higher death rates of infants following a change in the male membership of the group. It is proposed that this is a result of infanticide by the incoming male to clear out unrelated males and bring females into estrus sooner (Marsh, 1979). Though infanticide has been observed in the Tana River red colobus monkeys and other primate species, the causal relationship of infanticide and its relationship to reproduction and genealogy have yet to be fully determined. (Marsh, 1979; Newton and Dunbar, 1994; Oates, 1994; Struhsaker, 1975)
Lifespan is difficult to estimate because very few studies of these primates have ever lasted more than one year, let alone for an entire lifetime of one of these primates. Frequently only infant mortality is assessed. In one long term study the average infant/small juvenile mortality was, on average 0.064 deaths per infant per month. Infant mortality within the first year was as high as 55% for the population sampled. This same study found a higher mortality for males in the group than females, possibly from violent conflicts between group males and extra-group males for mating access and resources. (Marsh, 1979)
Other colobine monkeys rarely live longer than 30 years in captivity. It is likely that P. rufomitratus is like other members of the family Colobinae in this respect. Lifespans are likely to be even shorter in the wild. (Nowak, 1999)
Like most primates, P. rufomitratus is a noisy, social animal that lives in heterosexual groups. Typically, red colobus monkeys live in groups with between 30 to 50 members, including multiple males and females (Oates, 1994). However, in the reduced and fragmented habitat of the Tana River, the number of individuals in each group is much smaller, ranging from 12 to 30 (Marsh, 1979). In stark contrast to the rain forest species, Tana River red colobus often have only one or two males in the group. These demographics may give males greater access to mates and also indirectly reducing the stress on the limited resources of their fragmented habitat. The causes and implications of the small and fragmented Tana River habitat on behavior are still being investigated, but the differences between P. rufomitratus at Tana (small group size, low # of males) and the rain forest species are quite stark and fascinating.
The daily time budget of red colobus monkeys at Tana River differs significantly from the rain-forest species. They spend on average, the majority of their day resting (47.8%) or feeding (30.0%), and the rest of the time moving (7.2%), grooming (4.1%), or at play (3.4%). Feeding usually occurs during the early morning or late afternoon. This is typically followed by inactivity during the middle of the day and late evening. Though P.rufomitratus is mostly active during the day, observations of other red colobus species have indicated that some calling and sexual activity occur at night.
Like many primates, P. rufomitratus often engages in social behaviors such as play, aggression, and grooming (Struhsaker, 1975). Play can entail anything from chasing and wrestling to bouncing off of branches. Agonistic behaviors may be minor,such as a grimace, touch, or supplantation. These are often associated with a variety of body and limb posturing. Major agonistic behaviors often include stares and gapes usually with lunging, slapping or branch shaking, and in extreme cases, physical violence. These agonistic behaviors often occur between males in relationship to dominance and group status. In general, males groom each other more often than females, though the full effects of this behavior have not been examined for the small number of males in the Tana River red colobus species (Struhsaker and Leland, 1987). This pattern of male grooming is thought to arise because of the patrilineal organization. (Marsh, 1979; Oates, 1994; Struhsaker and Leland, 1987; Struhsaker, 1975)
Piliocolobus rufomitratus exhibits smaller home ranges than other red colobus monkeys (Marsh, 1979). The average annual home range of P. rufomitratus is near 9 ha compared to that of 34 to 114 ha for their counterparts. The average day range is 603 meters.
Like many primates, P. rufomitratus often engages in social behaviors such as play, aggression, and grooming (Struhsaker, 1975). Play can entail anything from chasing and wrestling to bouncing off of branches. Agonistic behaviors may be minor, such as a grimace, touch, or supplantation. These are often associated with a variety of body and limb posturing. Major agonistic behaviors often include stares and gapes usually with lunging, slapping or branch shaking, and in extreme cases, physical violence. These agonistic behaviors often occur between males in relationship to dominance and group status. In general, males groom each other more often than females, though the full effects of this behavior have not been examined for the small number of males in the Tana River red colobus species (Struhsaker and Leland, 1987). This pattern of male grooming is thought to arise because of the patrilineal organization. (Nowak, 1999; Struhsaker and Leland, 1987)
Piliocolobus rufomitratus is primarily a folivore, and this is related to a complement of morphological adaptations to this kind of diet. All colobine monkeys are distinguished from other old world primates in that they posses a ruminant-like stomach rather than a simple stomach. This stomach consists of a large sacculated chamber with a forestomach alkaline/acid system designed to digest plant matter using bacterial fermentation (Chivers, 1994). These primates also have high cusped, ridged molars designed to shear and fold leaves and seeds. This helps break down cell walls and extract the nutrients contained within (Teaford and Lucas, 1994).
Piliocolobus rufomitratus is primarily a folivore, though it feeds on a variety of other plant matter including fruits and flowers. In a study of diet choice, Tana River red colobus fed not only on young leaves (36%), but fruit and seeds (25%, mostly large and unripe), leaf buds (16.4%), mature leaves (11.5%) and flowers (6.2%). The top three plant species eaten were Ficus sycomorus (29.4%), Sorindeia obtusifoliolata (19.6%) and Acacia robusta (15.0%). These species contribute the majority of the diet of Tana River red colobus monkeys (Marsh, 1981a; Marsh, 1981c).
Studies of the impact of plant phytochemistry on dietary choice have found that the young leaves predominately chosen are higher in nitrogen (protein) content and lower in hard-to-digest fiber than the more abundant, mature leaves. Thus P. rufomitratus relies mostly on seasonal young leaves, flowers and fruits when available and reverts to mature leaves when necessary. Piliocolobus rufomitratus rarely eats the leaves of Diopyros mespiliformis despite that fact that this is the most common tree in their habitat. This might be due to the secondary compound napthoquinone, a phenolic toxin produced in the leaves (Mowry et al., 1996). (Chivers, 1994; Marsh, 1981a; Marsh, 1981c; Mowry, et al., 1996; Teaford and Lucas, 1994)
Piliocolobus rufomitratus has very few predators due to its large size and arboreal lifestyle. Presumably the pelage, dark red dorsally and lighter ventrally, helps to camouflage the shape of these monkeys when viewed from above and below, blending them into the forest branches when viewed from above and the sky and canopy when viewed from below.
In the rain forest species of red colobus, where predation pressures from chimpanzee hunting are significant, these animals often exhibit male-male bonding, swamping and aggression against chimpanzee hunting parties (Struhsaker, 1975). However, Tana River red colobus, which do not experience this pressure, do not exhibit these behaviors. Alarm calling in the form of a loud bark is a common defense against predation. Unfortunately they have few adaptations against their primary predators, humans. Fragmentation and reduction of habitat exposes Tana River red colobus to bushmeat traders (Oates, 1994). (Oates, 1994; Struhsaker and Leland, 1987)
Piliocolobus rufomitratus is host to a variety of parasites, though the exact number and species are not known. They also may influence plant growth and flowering patterns in their food species as some plant species may bloom synchronously to limit the impact of P. rufomitratus feeding. (Oates, 1994)
Tana River red colobus could be used for ecotourism. Although they are not as sought after by tourists as are the great apes, they are nonetheless a very prominent and interesting species. They are also often used as a source of food for humans in the bush meat trade. (Medley, 1993; Struhsaker, 1975)
There are no known adverse effects of P. rufomitratus on humans.
Tana River red colobus monkeys are listed as critically endangered by IUCN because their extremely fragmented habitat is under the constant threat of human encroachment (IUCN Website, 2001). The small tract of forest surrounding the river is primarily exploited for agriculture uses but also for canoe construction. Cattle feeding, intentional burns to increase grass production, and dam construction have also detrimentally altered the habitat on the Tana River.
These primates prefer interior forest habitat (Medley, 1993). Alterations to the forest that result in fragmentation, reduction of forest area and increase peripheral exposure adversely affect populations. A population census found that between 1975 and 1985, populations declined by 80% mostly due to these habitat loss (Decker & Kinnaird, 1992). Conservation efforts should focus on maintaining the integrity of the interior forest and reducing the causal factors of fragmentation. (Decker and Kinnaird, 1992; IUCN, 2000; Medley, 1993)
Piliocolobus rufomitratus was previously considered a subspecies of a more widespread species of red colobus monkey (Nowak, 1999; Oates, 1994). They were also previously recognized under the name Procolobus rufomitratus. (Nowak, 1999; Oates, 1994)
Nancy Shefferly (editor), Animal Diversity Web.
Jeremy Jones (author), University of Michigan-Ann Arbor, Ondrej Podlaha (editor), University of Michigan-Ann Arbor.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
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
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
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.
union of egg and spermatozoan
an animal that mainly eats leaves.
A substance that provides both nutrients and energy to a living thing.
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 eats mainly plants or parts of plants.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
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).
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.
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.
breeding takes place throughout the year
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