Impact of land-use changes on the wildebeest migration in the northern part of the Serengeti-Mara ecosystem

Aim The study tests the hypothesis that land-use changes in Narok District have had an impact on the wildebeest population [Connochaetes taurinus mear nsi (Burchell)] in the northern part of the Serengeti-Mara ecosystem. Location The Serengeti-Mara ecosystem is a vast area of rangelands, straddl ing the Tanzanian-Kenyan border in East Africa. The area is home to some 1. 3 million wildebeest, of which some 30,000 animals currently reside in the Kenyan part of the ecosystem. Methods We analysed the temporal changes in the wildebeest population in th e Kenyan part of the Serengeti-Mara ecosystem and their relationship with p ossible driving forces of change, such as rainfall, normalized difference v egetation index (NDVI), livestock numbers and land-cover changes. Changes i n the spatial distribution of wildebeest for three periods were compared wi th spatial changes in livestock distribution and land cover. The analyses w ere repeated for the Tanzanian part of the ecosystem and results compared. We thus tested the relative importance of land-use changes among the differ ent potential driving forces of change in the wildebeest populations. Results The wildebeest population in the Kenyan part of the Serengeti-Mara ecosystem declined drastically over the past 20 years and is currently fluc tuating around an estimated population of 31,300 animals, which is about 25 % of the population size at the end of the 1970s. The wildebeest population in the Kenyan part of the Serengeti-Mara ecosystem has, over the last deca des, been controlled by food supply during the dry and the wet seasons. Exp ansion of large-scale mechanized wheat farming in the Loita Plains since th e early 1980s has drastically reduced the wildebeest wet season range, forc ing the wildebeest population to use the dryer rangelands in the south-east ern part of the Loita eco-unit, or to move to the Mara eco-unit, where comp etition with cattle is higher. The expansion of the farming area has not in fluenced the size of the total cattle population in the Kenyan part of the study area, nor its spatial distribution. The much larger migratory wildebe est population of the Serengeti, in Tanzania, has not been affected by a do wnward trend from the late 1970s and is regulated by food supply in the dry season (Mduma et al., 1999). Around the Serengeti, in Tanzania, land-use c hanges are much less widespread, occur at a lower rare and affect a much sm aller area compared with the Kenyan part of the ecosystem. Moreover, land-u se changes around the Serengeti have taken place away from the main migrati on routes of wildebeest. Conclusions Over the last decades, the decline in the Kenyan wildebeest pop ulation did not seem to affect the much large Serengeti wildebeest populati on. However, if more land were to be converted to large scale farming close r to the Masai Mara National Reserve, the dry season range for both the Ken yan and the Serengeti population would he reduced. This might have serious consequences for both populations and therefore for the entire Serengeti-Ma ra ecosystem.