Population trends of resident wildebeest [Connochaetes taurinus hecki (Neumann)] and factors influencing them in the Masai Mara ecosystem, Kenya

Abstract

Population trends of resident wildebeest (Connochaetes taurinus hecki (Neumann)) and factors influencing them in Masai Mara ecosystem between 1977 and 1997 were investigated. Population trends were analyzed using aerial census data collected through systematic reconnaissance flights. Aerial censuses pertaining to resident wildebeest populations (non-migratory) were identified from migratory populations through spatial analysis. Regression analysis was used for population trend analysis. The impact of land use changes on wildebeest population was analyzed by comparing changes in wildebeest densities in cropped and non-cropped areas. Relationship between population size and rainfall fluctuations was used to assess the influence of rainfall on trends. Comparison of cattle densities in cropped and non-cropped areas was used to get an insight into possible competition between cattle and wildebeest for food. The results show that resident wildebeest population in the Masai Mara ecosystem has declined from about 119,000 in 1977 to about 22,000 in 1997, an 81% decline. The decline is mainly attributed to loss of former resident wildebeest wet season grazing, calving and breeding ranges to agriculture. Rainfall fluctuations and possible competition between wildebeest and cattle during periods of limited food resources may have further contributed to the decline.

Introduction

The Masai Mara National Reserve (MMNR) and adjoining group ranches (hereafter referred to as Masai Mara Ecosystem) in Kenya, form the northern portion of the Serengeti–Mara ecosystem to which wild animals (especially wildebeest and zebra) migrate annually. The ecosystem has the richest wildlife resources and offers the most spectacular wildlife watching in Kenya (Stelfox et al., 1986). These rich wildlife resources to a certain extent depend on the facilitation process maintained by annual migration of wildebeest and zebra. The wildebeest and zebra from Serengeti National Park migrate and stay in the Masai Mara ecosystem between June and November (Maddock, 1979). They occupy mainly the reserve and the adjoining group ranches. The resident wildebeest population also migrate between the reserve and the adjoining dispersal areas (Fig. 1) within the ecosystem. These migrations clearly show that the protected area (the reserve) is not adequate for the protection and viability of migratory wildlife species in the ecosystem. Rarely can wildlife parks be established so as to encompass an entire ecosystem. For this reason the viability of wildlife inside most protected areas is frequently influenced by outside factors (Jansen, 1986).

Habitat fragmentation or complete habitat loss is thought to be responsible for many wildlife species becoming endemic or extinct (Prins and Olff, 1998, Caughley and Sinclair, 1994). Prins and Olff (1998) note that an ecosystem that becomes smaller due to areas being put under cultivation (where wild grazers cannot occur any more) will show a decrease in species packing. This is the result of increased competition, although local extinctions may play a role too. Norton-Griffiths (1995) also notes that wildlife managers are most concerned about the conversion of privately owned rangelands to agriculture and ranching. Lado (1996) observes that the most serious long-term threat to the future of wildlife populations in Kenya is the indirect effects on habitat resource destruction or alteration. In Africa, the increasing conversion of natural lands to agriculture and human settlements is mainly attributed to increasing human population and is thought to be responsible for the increasing decline in wildlife resources (Johan, 1995).

The wildebeest is a flagship or keystone species in the Masai Mara ecosystem because of its occurrence in large numbers and its annual migrations within and outside the ecosystem (Talbot and Talbot, 1963, Sinclair, 1995). Their migration generate, through their grazing activities, optimal conditions for other large mammals, a process generally referred to as facilitation (Bell, 1970, Bell, 1971, Prins and Olff, 1998). This facilitation can only be sustained through regular migrations between protected and dispersal areas. However, the dispersal areas are increasingly being converted from pastoral grazing areas to agricultural and human settlement areas (Sinclair, 1995, Norton-Griffiths, 1995). For example, between 1975 and 1995, the area under wheat in the Masai Mara ecosystem has increased from 4875 ha in 1975 (Karime, 1990) to 11,000 ha in 1985 to 50,000 ha in 1995 (Serneels et al., in press). The long-term impact of these land use changes on the population of the wildlife species (especially the migrants) has not been studied. However, a number of studies undertaken in the ecosystem indicate that populations of most wildlife species are on the decline (Ottichilo et al., in press, Grunblatt, Said and Warugute, 1996, Broten and Said, 1995, Sitati, 1997).

In this study we analyze the trends of the resident wildebeest population in Masai Mara ecosystem over the past 20 years (1977–1997). We further analyze the relationship between crop (wheat) expansion, rainfall fluctuations and cattle density and wildebeest population trends.