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The red colobus (Procolobus kirkii) is one of the most beautiful monkeys I know, with a shiny brick-red coat and a mane of long white hair. It is a restricted-range species found only in the red mahogany trees and coral rag forests of Zanzibar. This is one of the world’s rarest primates and it is endemic to the Zanzibar archipelago. At the time of my arrival in Zanzibar in 1993, the population was variously estimated at between 1,500 and 2,500 individuals. However, since then it has declined drastically and now hovers at around 1,500. The main reason for this is compression of their forest habitat by the burgeoning human population. Today, the population is split into a large number of small, isolated groups and it is difficult to get an accurate estimate of numbers. This has led to a high degree of genetic differentiation across the population as a whole, and some of the subpopulations may be classified as distinct sub-species or even distinct species. This phenomenon has never been systematically studied. Red colobus are highly arboreal and seldom come to the ground. They are primarily folivorous, with most of their diet being leaves, and the bulk of their feeding occurs in the early morning and around dusk, with a long sleep in between. This elusive and retiring nature, combined with the fact that they can disappear into surprisingly small patches of forest, make them difficult to study. Although there are some small remote islands that still have large undisturbed tracts of forest in which red colobus are abundant, these islands are infrequently visited by tourists. Because of this, the Jozani-Chwaka Bay National Park remains the best place to see them for casual visitors to Zanzibar. However, despite the fact that the red colobus is the Zanzibar’s flagship species and is the chief attraction for visiting many foreign and local tourists, it is not very well served by the national park system and there are few protected areas dedicated to the conservation of this monkey. In the late 1990s, the severity of habitat loss forced some red colobus to begin using mangrove trees or even coming to the ground in some areas to feed, and there is a real fear that this trend might continue.
The scientific description of the red colobus details coat color, body size, sex differences, and dental formula. An average adult male is 410 mm and a female 390 mm. Zanzibar red colobus show sexual dimorphism in that males are noticeably larger than females. Males typically weigh 7.0 kg and females 5.7 kg. The convenient method to measure body size is to use the average body mass index. This is measured by the weight in kilograms divided by height in meters squared. The Zanzibar red colobus weighs in at 20.8 with the lower limits being 18.8 and the upper 24.2. The most striking difference in comparison to other red colobus is coat color. Adult Zanzibar red colobus can depict different shades of red, but the dominant color is a deep chestnut. This is due to the presence of pheomelanin in the hair strands. In contrast, other red colobus have black hair with pheomelanin giving them a golden appearance. Other physical characteristics of Zanzibar red colobus include a face which is hairless with the exception of a few short white hairs. This results in a pinkish coloration which is made more prominent as these animals are able to blush due to high socioeconomic flexibility. Ousting of other guenon species and occasional intergroup aggression has resulted in a species which is less accepting of conspecifics. High SES has also resulted in decentralization of the stomach and a more enlarged brain. Due to its small fragmented range and island evolution, Zanzibar red colobus is a highly specialized species with several unique adaptations.
Given the relatively small size of Zanzibar and consequently the size of the two forests, the high density of predators has probably been the major selective force acting on the colobus. Two primary defences have evolved against this, both passive and both arboreal. The passive defence is camouflage, and the colobus is the only primate in the two forests with a conspicuous and distinctive colouration. The selective pressures for this must have been intense, as the two other arboreal monkeys, both of which probably entered their present habitats at about the same time as the colobus, both have duller pelage and sexual dichromatism in their body and/or face. A conspicuous precisely demarcated coat with sex and age-specific differences probably only affords good camouflage against a specific background and are clear indicators of uniformity and/or changes in predation pressures. This is well illustrated by the genus Presbytis, a montane forest specialist with a complex structure and probably high predator densities, having evolved highly variegated pelage with coat patterns approaching the ultimate in colobine counter shading.
The best place to see Zanzibar red colobus is undoubtedly in Jozani forest, in the centre of the island. The forest is a true natural wonder, with tall trees and swamp areas and is home to many other species of animal and bird life. Many Zanzibar tour companies arrange trips to Jozani forest. Prices vary widely, with guides being available at the entrance on an ad-hoc basis. In the past, some of these guides had little or no knowledge of the colobus and in their eagerness to do a job would scare the animals out of the trees for tourists to get good photos. But on our recent visit, we found the guides to be better informed and keen to do their job without causing damage to the wildlife. A more reliable way to get a knowledgeable guide is to book in advance. This way, the guides can expect regular work with the tour company and not pester other tourists who may or may not want a guide. The guides all have a depth of knowledge about the forest, its flora and fauna, and many of them are involved in local conservation initiatives aimed at preserving the forest and its monkeys. An experienced and knowledgeable guide can really add to a visit to the forest. He can tell you about all aspects of the life of the colobus, from what they eat and how they find it, to how the males compete for dominance, and the females in their search for the highest quality food for their offspring which influences their reproductive success. Guides will be more than happy to converse with you, answer your questions and show you and tell you everything they know. They will also be able to show you other areas in Zanzibar where they participate in conservation and aid R&R for forest areas that have been lost to agricultural development. Be aware also that this is somewhat of a hotspot for mosquitoes and a low risk of malaria, more so than in the other areas of Zanzibar. An insect repellent is a must!