This thesis deals with the dynamics of large herbivores in the Masai Mara ecosystem in Kenya. The study area is famous for the annual migration of wildebeest and common zebra from and back to the Serengeti in Tanzania. In this study we made a distinction between these two migratory species and the other non-migratory wildlife species. The results reported are based on animal population estimates derived from counts made on board of small light aircraft. The study covers the period from 1977 to 1997. The total of non-migratory wildlife species in the Masai Mara ecosystem declined by 58% in the last 20 years. The decline ranged from 49% in small brown antelopes to 72% in medium brown antelopes. In individual species, the decline ranged from 52% in Grant's gazelle to 88% in the warthog. The population sizes of the elephant, impala and ostrich remained constant during the analysis period. There was no significant difference in the decline of wildlife inside and outside the Masai Mara National Reserve except for Thomson's gazelle and warthog. The population sizes of all livestock species except for the donkey did not significantly change during the entire analysis period. A large proportion of wildebeest migrates between the Serengeti and the Masai Mara ecosystem. A smaller population migrates between the Masai Mara National Reserve and the Loita plains in the north. Statistical analysis revealed that the size of this so-called "resident" wildebeest population declined by 81% over the last 20 years. Further analysis revealed a remarkable association between the decline in resident wildebeest population and the expansion of wheat farming into prime and original wildebeest habitat in the Loita plains. We therefore conclude that loss of former wildlife habitat to agriculture was responsible for the drastic decline of this resident wildebeest population. Apart from habitat loss to agriculture, droughts, poaching and possibly competition between wildlife and livestock may have further contributed to the decline. We argue that these factors and agricultural encroachment may have been responsible for the reported decline of the non-migratory species as well. In the last chapter of this thesis we studied a number of environmental factors that could be associated to the migration of wildebeest and common zebra. We found a significant relationship between wet season rainfall in Kenya and the size of the wildebeest and zebra population migrating into the Masai Mara ecosystem. We also found a significant relationship between dry season NDVI and the size of wildebeest population migrating into the Masai Mara ecosystem. We concluded that wet season rainfall and availability of food in the dry season influence the migration into the Masai Mara ecosystem. We also concluded that NDVI could be used for monitoring and predicting the movements of migratory wildebeest populations in the Serengeti-Mara ecosystem. In this thesis we report an alarming decline of most wildlife populations in Masai Mara ecosystem over the past 20 years. Furthermore, we made it plausible that this decline was related to habitat loss, due to agricultural encroachment. Socio-economic surveys not analyzed in this thesis but reported elsewhere, indicated that the local people in the areas adjoining the Masai Mara national Reserve anticipate that they will put their hands to the plough once land adjudication process will be completed. The impact of this would be a further decline and possibly a complete collapse of the wildlife populations for which the Masai Mara is reputed. Therefore, it is extremely urgent that a balance be struck between wildlife conservation and this alternative land-use if the current downward wildlife population trend is to be reversed. Lastly the current Kenyan legislation prohibits on one hand the killing of wildlife, while on the other hand leaving the option open for unlimited destruction of its habitat. The reported decline of the resident wildebeest population is in our view is a direct result of this gap in the legislation. We argue that it is urgent to reconsider the wildlife conservation policy and adjust its legislation such that it would be possible to protect wildlife habitat outside the protected area system from further undesirable destruction.
