Procolobus verus

104.

Olive Colobus

Procolobus verus

French: Colobe vert / German: Griiner Stummelaffe / Spanish: Colobo oliva

Other common names: Green Colobus, Van Beneden’s Colobus

Taxonomy. Colobus verus Van Beneden, 1838,

Africa.

This species is monotypic.

Distribution. West Africa, from SE Sierra Leone and S Guinea to Ghana (extending just E of the Volta River), and in S Togo, S Benin, and S Nigeria (S bank of the River Benue just above its confluence with the Niger River in the Idah, Kogi State, and the lower Niger). There is a discontinuity in the distribution between the VoltaRiver in Ghana and the Nigerian population, and it is believed that its range was far greater in the recent past.

Descriptive notes. Head-body 46-51 cm (males) and 38-55 cm (females), tail 50-61 cm (males) and 43-71 cm (females); weight 4.5-7 kg (males) and 3.4-2 kg (females). The Olive Colobus is the smallest of the colobine monkeys. On the basis of hunter-shot specimens and museum records, J. Oates and colleagues gave the following body weights: males 4-7 kg (4.5-7 kg; n = 20) and females 4-2 kg (2.8-5.4 kg; n = 14). The Olive Colobus is generally a dull olive-brown dorsally, becoming grayish-white below and on limbs. Head is small and rounded, with a virtually hairless face and an off-white circumfacial ruff. There is a low longitudinal crest of upright hairs on the crown (more pronounced in the male), which is formed by a pair of lateral pale whorls. Tail is slender and untufted. Feet are enormous and can equal as much as onethird the length of the entire hindlimb. Thumbs are mere tubercles. Ischial callosities remain separate in both sexes.

Habitat. Swamp forest, moist forest, dry semi-deciduous forest, dense regenerating forest, and abandoned farmland. The Olive Colobus prefers dense tangled growth in the lower levels of the forest canopy, and it is especially common in swampy riparian forest. It is rarely seen in undisturbed high forest and avoids feeding in the crowns of tall trees and going to the ground.

Food and Feeding. The diet of the Olive Colobus is composed mainly of young leaves from trees and climbing plants. Liana leaves are a year-round staple. Seeds and flowers are also important. In a 1988 study by J. Oates in Tiwai Island Wildlife Sanctuary, Sierra Leone, a group of Olive Colobus were highly selective feeders. The group ate from a small number of uncommon middle canopy trees, from the understory, and from climbers. Their food trees tended to be deciduous or produce large crops of new leaves over a short period of time. Unlike other colobus monkeys, mature leaves were largely ignored. They were eaten in small quantities only toward the end of the dry season when preferred items (young leaves and seeds) were least available. They obtained their year-round staple from young leaves; seeds, flowers, and leaf petioles were important seasonally. In the dry season, availabilities of seeds are higher and young leaves lower. Young leaves of Terminalia iworensis (Combretaceae), Sapium aubreville: (Euphorbiaceae; young leaves and mature leaf petioles), and Acacia pennata (Fabaceae) were predominant in the diet. Their preferred leaves tended to have low fiber and tannin levels. Overall 50 plant species were included in the diet. They did not seem to look for or eat small insects.

Breeding. Even before the advent of puberty, the female Olive Colobus begins to exhibit a substantial pink perineal swelling during the periovulatory period; a similar swelling is described for newborns. Females carry conspicuous sexual swellings for c.50% of their menstrual cycle, and this makes them conspicuous to males. Females are strongly proceptive and mate overwhelmingly with the dominant male in a group. Subadult males have a perineal organ. The Olive Colobus is, to some extent, a seasonal breeder, with a mating season in April-August and births in November-February after a gestation of 150-180 days. A single young is born. Female Olive Colobus are unique among Old World monkey mothers in that they carry their newborns dangling from their mouth for the first few weeks. Neonatal pelage resembles that of the adult, but it is slightly lighter and a bit more yellow.

Activity patterns. The Olive Colobus is diurnal and almost exclusively arboreal. It is very shy. At Tiwai Island Wildlife Sanctuary, it spent 40% of its day resting, 27% feeding, 25% moving, and 8% engaging in social and other activities.

Movements, Home range and Social organization. Average daily movement has been recorded at 1200 m, with home ranges of 28-58 ha. The Olive Colobuslives in small groups of 5-20 individuals (but usually under ten), with 1-2 adult males and the same number of adult females. Group membership is relatively fluid, with young individuals of both sexes dispersing from their natal groups, although adult females change groups more often than do adult males. The Olive Colobus is almost always found in close association with guenons (Mona, Cercopithecus mona, Spot-nosed, C. petaurista, Campbell's, C. campbelli, and Diana, C. diana, monkeys), and it responds to their alarm calls. These associations with other species are invariable, particularly with Diana Monkeys. Each Olive Colobus group follows “its” Diana Monkey group around, and territorial encounters between groups of Diana Monkeys bring their associated Olive Colobus into proximity, resulting in territorial counter-calling by adult males and extragroup matings.

Status and Conservation. CITES Appendix II. Classified as Near Threatened on The IUCN Red List. The Olive Colobusis listed as Class A in the African Convention on the Conservation of Nature and Natural Resources. It is probably declining in numbers because of widespread loss of habitat and hunting for food, especially in the far eastern part of its distribution toward Nigeria. Their cryptic nature and ability to survive in swamps and small forest fragments and to adapt to some anthropogenic disturbance have no doubt enabled them to persist and remain common in at least parts of their range. The Olive Colobus occurs in Bia, Kakum, and Nini-Suhien national parks, Bomfobiri Wildlife Sanctuary, Ankasa Game Reserve, and Sukusuku Reserve in Ghana; Tai Forest National Park in Ivory Coast; Mount Nimba Strict Nature Reserve and Sapo National Park in Liberia; and Gola Forest Reserves and Tiwai Island Wildlife Sanctuary in Sierra Leone.

Bibliography. Booth (1956b, 1957a), Groves (2001, 2007b), Grubb et al. (2003), Hill (1952), Korstjens & Noé (2004), Korstjens & Schippers (2003), Menzies (1970), Oates (1981, 1988a, 2011), Oates & Whitesides (1990), Oates et al. (1990).