De Brazza's monkeys (Cercopithecus neglectus) in Kenya Census distribution and conservation.код для вставкиСкачать
American Journal of Primatology 8:269-277 (1985) De Brazza’s Monkeys (Cercopithecus neglectus) in Kenya: Census, Distribution, and Conservation E. JEAN BRENNAN University of Pennsyluaniu, Uniurrsity Museum Philadelphia, and Institute of Primate Research, National Museums ofKeenyq Nalrobh Kenya The population of De Brazza’s monkeys (Cercopithecus neglectus) in Kenya, East Africa, was surveyed from May to September of 1983 to estimate its numbers, distribution, and conservation status. A small number of De Brazza’s monkeys are protected within Saiwa National Park; however, the vast majority of the population is endangered because they are restricted to small, isolated pockets of forests amid expanding farmland within the TransNzoia area of western Kenya. A few animals are found on the slopes of Mt. Elgon and on the Cherangani Hills, although these areas offer little protection. The pressures now facing this population are loss of habitat, reproductive isolation, and a decline in numbers as the result of being killed, either as a food source or as agricultural pests. If the current situation continues and no attempt is made to conserve the remaining De Brazza’s monkeys, the species faces almost certain extinction in Kenya. Key words: De Brazza’s monkey, Cercopithecm neglectus, survey, conservation, Kenya INTRODIJCTION The De Brazza’s monkey (Cercopithecus neglectus,) has a wide geographic distribution across Africa [Hill, 1966; Kingdon, 1971; Meester & Setzer, 19711, with several isolated populations existing in both the main equatorial forest and in East Africa [Tappen, 19601. However, with the exception of studies in Gabon [GautierHion & Gautier, 1978; Quris, 19761 and Kenya [Simpson, 19701, little work has been done on natural populations of De Brazza’s monkeys. The status of this species is unknown over most of its range [Wolfheim, 19831. In Kenya, distribution of De Brazza’s monkeys is restricted to the western region, north of lake Victoria [Kingdon, 19711. This area includes the Trans-Nzoia Plain, with the Cherangani Hills on the eastern border and Mt. Elgon on the western border (Fig. 1). The vegetation in this area once consisted of long, narrow strips of riverine forests forming a matrix between Mt. Elgon and the Cherangani Hills. However, much of the forested land was cleared for agricultural purposes by the European settlers, and by the early 1960s, the status of the De Brazza’s monkey Received August 13, 1984; revision accepted Janaury 5 , 1985. Address reprint requests to E. Jean Brennan, Institute of Primate Research, P.O. Box 24481, Karen, Kenya. 0 1985 Alan R. Liss, Inc. 270 Brennan Fig. 1. Map of Kenya showing lands at recorded forest coverage (study area within dashed lines). Inset: Kenya’s position in t he African continent. population in Kenya was reported as threatened [Booth, 1962; Hill, 1966; Leakey, 19691. Since that time, the amount of forest habitat in the west has continued to decrease. Following Kenyan independence in 1963, most of the land previously held as large estates by Europeans settlers was returned to traditional tribal ownership, divided into small plots, and sold to private individuals for subsistence farming. These small farms are now cultivated by hand, and the forested areas that were once inaccessible to the farm machinery used by the European colonials are being cleared by native farmers. Clearing exposes the most vulnerable areas along streams and rivers to a greater amount of run-off and results in a n increase in water flow. This causes the streams to trench down, the water table to drop, and the riparian vegetation to be replaced with less productive, more xeric plant species [Behnke & Raleigh, 19781. Primate conservationists in Kenya fear that these changes may have served to accelerate the already rapid decline in the De Brazza’s monkey population. Thus, at the request of the Institute of Primate Research of the National Museums of Kenya, I conducted a four-month survey of De Brazza’s monkeys in Kenya. The purpose of the survey was to estimate their number and distribution to document the extent of the pressures threatening their survival, and to provide information that would aid future conservation efforts. One idea under consideration locally was the transloca- De Rrazza’s Monkeys in Kenya 271 tion of threatened groups of De Brazza’s monkeys into Saiwa Swamp National Park, Mt. Elgon National Park, or the National Forests on The Cherangani Hills. The results of the survey are presented, and in light of the findings a possible conservation strategy for the De Brazza’s monkey and its habitat in Kenya is discussed. METHODS The survey was carried out in three phases: reconnaissance, census of the TransNzoia area, and evaluation of Saiwa Swamp National Park. Reconnaissance The first pahse involved a reconnaissance of the western districts in order to establish the present range of De Brazza’s monkeys. During this phase, I traveled with a Kenyan research assistant to 115 different sites and, using black-and-white photos, asked the local people to identify the types of monkeys in the area. In order to assure positive identification, the people were asked to identify each species from the photo and to describe its color. The total area included in the survey was 3,304 km2 (near the city of Kitale, latitude 01” 00”; longitude 35” OO’E). Census The census phase involved more extensive examination of sites than was conducted during the reconnaissance phase. An area was censused if there was forest remaining (even though De Brazza’s monkeys had not been reported there) or if people reported having seen the species. Fifty such sites were censused during the course of this study. The technique used was the trail survey method [Mittermeier, 1973; Neville et al, 1976; Wilson & Wilson, 19751. All forest surveyed happened to be located along rivers and streams. Each had an extensive trail system cut by the local people in order to gain access to streams for drawing water or as pathways for livestock. Since these trails were designed to provide the most direct access route to rivers and streams, they not only followed but also cut across the contours of the land. Census data included group size, age-sex composition, behavior, time, and location. The criteria used to determine sex was base on sexual dimorphism in size [Hill, 1966; Gautier-Hion & Gautier, 19781 and the visibility of the male’s blue scrotum. Age was recorded by general classification (adult, juvenile, infant) according to coat color [Hill, 1966; Stevenson, 19731. If a n animal could not be tracked long enough to verify its age or sex, it was recorded as “unknown.” In addition to census information, a general description of the forest and the surrounding area was obtained. The amount of habitat lost over the last 15 years was calculated by comparing the amount of forest remaining with the amount indicated on maps based on 1968 aerial photos (D.O.S. 423 Series Y731). Other information included in the site description was the proximity of the forest to cultivation, whether the forest was being cleared or its understory being grazed by livestock, and whether there was any evidence of trapping or hunting with the area. Whenever possible, the people who owned the land or lived on farms surrounding the forest were interviewed. During the interview we asked their plans for using or clearing the forest and whether they were experiencing crop raiding by primates. If crop raiding was occurring, we asked by which species and what if any methods were being used to control or harvest the primates in the area. Evaluation of Saiwa National Park A general evaluation of the park’s habitat and a census of its De Brazza’s monkey population was conducted as the final phase of the survey. The habitat 272 Brennan evaluation consisted of classifying and mapping the different types of vegetation using a compass and rangefinder. Censusing was carried out with the help of three Kenyan field assistants and was repeated on four consecutive days. The park was divided into four quadrants WE, NW, SE, and SW). Members of the team simultaneously began the census at a common point (at the swamp edge where the quadrants met) and then walked through their respective quadrants. Each member moved through his area in a similar pattern; for example, the person covering the NE quadrant moved first to the north, away from this common point for a distance of 60 m, and then moved across the park from west to east. Upon reaching the park boundary, the surveyer continued north for another 60 m before repeating the pattern by crossing the park from west to east. During this time all sightings of De Brazza’s monkey were recorded, inlcuding the group’s size, age-sex composition, time, and location. Climate The climate of western Kenya, unlike that of central and eastern Kenya, does not show the typical bimodal pattern of long and short rains. Instead, there is a marked wet and dry season. The rains usually begin in March or April and continue into August, with June generally being a drier month. Rainfall data recorded at Mt. Elgon National Park, Saiwa Swamp, and Kimothon Forest Station (located on the Ne slope of Mt. Elgon) were collected from daily records kept by the National Park and Forest Service personnel. Annual rainfall averaged over a five-year period from 1978 to 1982 is presented in Figure 2. The average annual rainfall for each of these sites is as follows: Mt. Elgon, 1,312 mm; Saiwa, 1,125 mm; and Kimthon, 899 mm. RESULTS Trans-Nzoia The total number of De Brazza’s monkeys found within the Trans-Nzoia area, including Saiwa National Park, was 82. Excluding Saiwa National Park, De Brazza’s monkeys numbered 54 and were found a t 17 sites in groups ranging in size from one to six members (Table I). In West Africa De Brazza’s monkeys are reported to be monogamous although this characteristic may not apply to the Kenyan population AVERAGE MONTHLY RAINFALL 0 KIMOTHON SAIWA El M T ELGON Fig. 2. Annual rainfall averaged over a five-year period from 1978 to 1982 at Mt. Elgon National Park, Saiwa Swamp, and Kimothon Forest Station. ne Brama’s Monkeys in Kenya 273 TABLE 1. Census Data* AM AF or SAM (size) Site (scrotum) 1 2 2‘ 3 4 5 5’ 14 15 20 24 34 40 41 42 42‘ 43 1 1 1 3 Total 9 24 AF (nipples) Juv Inf Unk 1 4 2 1 1 5 6 1 3 1 2 1 2 2 1 1 1 1 1 1 2 1 1 2 Total 1 1 3 3 2 2 2 2 1 3 6 4 3 2 2 1 3 2 4 6 2 2 5 5 m 5 54 *On De Brazza’s monkeys within Trans-Nzoia area (excluding Saiwa National Park). AM, adult male; AF,adult female; SAM, subadult male; Juv, juvenile; Inf, infant; LJnk, unknown. [Simpson, 19701. An additional twenty-one sites were reported to have De Brazza’s monkeys, although these areas could not be adequately censused during the survey period. Multiplying twenty-one (the number of uncensused sites) by 3.2 (the average number of De Brazza’s monkeys seen per censused site) would suggest that there are approximately sixty-seven additional De Brazza’s monkeys in the area surveyed. Other species of diurnal primates seen during this survey were black and white colobus (Cobbus querezu), blue monkeys (Cercopithecus mitis), and vervet monkeys (Cercopithecus aethiops). The Trans-Nzoia Plain is a densely populated agricultural area, and the De Brazza’s monkeys found there live in isolated forest pockets amidst expanding farmlands. These forests can be classified as riparian with a high, dense shrub or herb layer and a n abundance of lianas and epiphytes. A typical forest pocket containing De Brazza’s monkeys is 20-40 m wide and between 60 and 200 m long. All of these remnant strips of forest are on privately owned land that is rapidly being cleared or, according to development schemes, is soon to be cleared. Forests are selectively logged for timber, although most trees are cut down for making charcoal (the country major fuel source) and much of the forest understory is cut for use as firewood. The estimated forest loss for the censused areas over the last 15 years is between 50% and 90%. In addition, every forest surveryed contained snares or traps commonly used by one of the three tribes (Mt. Elgon Masai or Sebei, Kakamega, and Wagishu) who hunt monkeys for meat. Other tribes, such as the Pokot and Kalenjin, report that they hunt monkeys with bows and arrows as a means of protecting their crops. Thus, monkeys who live in marginally productive habitats are faced with a double-jeopardy situation: they are rapidly losing their food resources (which are either being grazed or cut out), and if they turn to crop raiding in order to survive, they run the risk of being killed by local farmers. 274 Brennan Saiwa National Park The De Brazza’s monkey is legally protected throughout Kenya; however, it appears that the law is being enforced only within Saiwa National Park. Because of this fact, Saiwa was a major focus of the survey and was studied intensively to evaluate the habitat and to determine the size of its population. Saiwa National Park, located within the Trans-Nzoia plain near the base of the northern Cherangani Hills, covers a n area of approximately 191.7 ha. The relatively narrow swamp varies between 90 and 360 m in width and extends for approximately 6 km [Owen, 19701. The banks of the swamp are covered with a mixture of habitat types that range from lush gallery forest to seasonally flooded, marshy grasslands. Five types of vegetation were identified, using the physiognomic classifications of Pratt and Gwynne . 37.75% swamp, 25.44% forest, 17.15% grassland, 15.66% bushland thicket, and 4.0% bushland (with a cleared understory). The census of Saiwa revealed that 28 De Brazza’s monkeys live in the park, consisting of five groups and one solitary male. De Brazza’s monkeys were found only within the forest or bushland thicket areas. Combined, these two vegetation types provide 78.8 ha of suitable habitat. Cherangani Hills The Cherangani Hills, which lie to the east of the Trans-Nzoia, are a residual mountain mass composed of metamorphic rocks with quartzite ridges [Mabberley, 1975; Oxford Expedition, 19711. The top ridge of the Cheranganis was a large forested area until the construction of an extensive road, known as the Cherangani Highway. This road bisected the forests along the range, and the clearing that took place as it was being built served to open the area up to squatters, who settled along the ridge and slopes. As a result, these areas were exposed to erosion, causing a change in plant communities. It is now difficult to describe the natural vegetation of the Cherangani Hills, as “only a few areas could be described as anything approaching ‘virgin’ . . . ” [Oxford Expedition, 1971:67]. Although Booth 119621 reported sighting De Brazza’s monkeys on the lower slopes of the Cheranganis, the species was never observed there during the present study, and, consequently, its current status could not be ascertained. Reports from local farmers and forest game scouts suggest that the species, although reduced in number, may still exist in the northern half of the Kapolet forest on the northwest slopes of the Cherangani range. This area had been subject to heavy poaching [Oxford Expedition, 19701, and the local people reported that they continued to hunt in the forest on the Cheranganis. Poaching may account , in part, for the failure to locate De Brazza’s monkeys during this survey. Thus, if the species still lives on the Cherangani Hills, its survival may be in question because of poaching and habitat destruction. Mt. Elgon Mt. Elgon is a dormant volcano that lies to the west of the Trans-Nzoia and straddles the Kenya-Uganda border. Historic references state that De Brazza’s monkeys were once “fairly plentiful on some of the south-eastern slopes of Mt. Elgon” [Pitman, 1954:511. Because of this, the Kenyan side of Mt. Elgon was surveyed to determine the current status of the species on the mountain and whether or not it occurs within Mt. Elgon National Park. Most of the Kenyan side of Mt. Elgon, excluding the 16,720 ha that make up the National Park, is under the control of the National Forest Department, which has cleared much of the natural forests and replanted the area with fast-gowing exotic trees. This style of forest management has changed the ecosystem on Mt. Elgon, De Brazza’s Monkeys in Kenya 275 threatening the survival of many endemic plant and animal species. These monocultures have replaced the natural forest vegetation with large, dense stands that inhibit the growth of understory plants. As a result, these areas do not retain rainwater effectively, are poor soil preservers, and, consequently, are of little value as wildlife refuges. The greater part of the mountain is now covered with these extensive monospecific stands of pine or cedar. The only indication that De Brazza’s monkeys may still inhabit Mt.Elgon stems from a report that a small group were shot in 1982 near the Kimothon sawmill along the Kimothon River north of the National Park at a n elevation of 2,320 m. There is, however, no record that De Brazza’s monkeys ever lived within the boundaries of Mt. Elgon National Park. Thus, within the last 30 years, the species has been all but extirpated from Mt. Elgon, and the few animals that remain are being hunted by local farmers. DISCUSSION In Kenya the De Brazza’s monkey is restricted to riverine forests in the western region of the country. This area also contains one of the most densely populated and fastest growing human communities in East Africa [Brown, 1981; Erhlich, 1980; Hickman et al., 19731. As a result, there is a n increasing demand for agricultural land and wood for fuel. The major threat to De Brazza’s monkeys is deforestation; however, the loss of forested land threatens not only the survival of De Brazza’s monkeys but also the livelihood of the people. The extent of forest clearing and the type of agriculture and forestry that is currently being practiced has exposed many areas to accelerated erosion. The result is that the complete loss of soil, or soil, if any remains, that is thin and poor in nutrients and has lost its ability to hold rainwater, advancing the erosion process even further. Ultimately, this changes the plant community and alters the biotic diversity of the riverine forests. Thus, it is impossible to consider the fate of De Brazza’s monkeys in Kenya without considering the future of the human population as welI. Any long-term conservation strategy for the De Brazza’s monkey must be part of a n integrated plan for the western region. A long-range conservation scheme for western Kenya that would protect the De Brazza’s monkey as well as provide for the quality of human life must reconcile nature conservation goals with human needs. Considering the preliminary nature of this study, it may be premature to recommend how this might be accomplished. Nevertheless, it is clear that first steps toward this goal would include: improving agricultural practices; restricting the harvest of forest,products to sustainable levels, ensuring that large-scale development projects are carefully planned, protecting the remaining forest, enforcing antipoaching and antigrazing laws, and rehabiliting eroded land. Given the current status of the De Brazza’s monkey population in Kenya and the extent of encroachment, a large percentage of the population may be destroyed before any long-range conservation plan can be implemented. Therefore, the design of a conservation plan should be organized in terms of triage: some animals will inevitably die; some will survive for a short time without any assistance; and others will survive only if a n immediate attempt is made to save them. Although translocation should be proposed only as a last resort, the present situation in Kenya warrants its consideration. Because the natural distribution of De Brazza’s monkeys has previously included area of Mt. Elgon and because the species is still found in one area on the mountain, the National Park should be evaluated as a possible translocation site. The fact that De Brazza’s monkeys have not been recorded within the park, however, suggests that other factors might account for their absence. For example, the species may be excluded from the park 276 Brennan by interspecific competition or unsuitable weather and habitat. Further research is needed to evaluate the floral, faunal, and environmental differences between Saiwa National Park, Mt. Elgon National Park, and the area on Mt. Elgon outside the park near the Kimothon Forest Station. CONCLUSIONS 1. The distribution of the De Brazza’s monkey in Kenya is restricted to the western districts between Mt. Elgon and the Cherangani Hills in the area known as the Trans-Nzoia Plains. 2. Owing to agricultural development, population size is limited and if current trends continue, the threat of local extinction resulting from loss of habitat, reproductive isolation, and hunting pressure is alarmingly real. 3. Any strategy aimed at long-term conservation of this species in Kenya must be a n integrated plan that would protect De Brazza’s monkeys while taking into account the needs of the local people. ACKNOWLEDGMENTS This work was sponsored by the Institute of Primate Research of the National Museums of Kenya and was supported through grants from the World Wildlife Fund-US, East Africa Wildlife Society, and Sigma Xi Research Society. I wish to thank the Republic of Kenya, OEce of the President, and the Ministry of Wildlife for permission to work in Kenya and in the National Parks. I am most grateful to Tim and Jane Barnley, Dr. Cunningham van Someren, and Dr. James G. Else. I am most especially grateful to Dr. Robert Harding, who helped and encouraged me through every phase of this study. REFERENCES Behnke, R.J.; Raleigh, R.F. Grazing and the riparian zone: impact and management perspectives, pp 263-267 in STRATEGIES FOR PROTECTION AND MANAGEMENT OF FLOODPLAIN WETLANDS AND OTHER RIPARIAN ECOSYSTEMS. R.R. Johnson; J.F. McCormick, eds. General Technical Report WO-12, Forest Service, U.S. Department Agriculture, Washington D.C., 1978. Booth, C. 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