|A lion in Kenya's Maasai Mara National Reserve (2008 photo)|
The study, conducted by the International Livestock Research Institute in Nairobi, and the World Wide Fund for Nature, monitored the population of six animal species each month between 1989 and 2003. The declines in the Maasai Mara National Reserve were dramatic, with the population of giraffes dropping by 95 percent, warthogs by 85 percent, and impala by 67 percent.
According to lead author Joseph Ogutu, similar trends have been observed for most other species in the Maasai Mara, which lies along Kenya's southern border with Tanzania. Only elephants and ostriches have escaped the pattern.
Ogutu says the phenomenon can be seen in other Kenyan wildlife parks as well. He also says the rate of decline has increased over the years, and is unlikely to have abated since the observation was concluded in 2003.
"The underlying factors which are causing this decline, like the land use change have become much more intense over time, so the human population is increasing there and the need for space to build more settlements for people and intensification of how people use the land," said Joseph Ogutu. "The trend must have continued up till now."
According to the researchers, the decline can be traced to the growing encroachment of human settlements on the land in and around the reserve. Ogutu says the Maasai, a traditionally semi-nomadic community, have been settling down in growing numbers in recent years, using an ever-larger amount of land to grow crops and graze livestock.
"An increase in the number of people alone does not lead directly to a decrease in the number of wildlife," he said. "Because these people have adopted a more settled lifestyle compared to a semi-nomadic lifestyle that they used to have in the past, it means that they are using the areas where they settle very intensively."
The study's authors point out that the Kenyan government's neglect of the Maasai community's concerns has encouraged them to give up elements of their traditional lifestyle.
The authors also say the government should put in place more coherent policies regarding what sorts of activities can be carried out on land around the reserves. Ogutu notes that in the Serengeti, the larger extension of the Maasai Mara across the border in Tanzania, where most of the surrounding land is publicly-owned, there have been far fewer problems with encroachment.