Masai Mara's hoofed mammals in decline

A giraffe beneath an acacia tree in Masai Mara National Reserve, Kenya. Scientists at the Nairobi-based International Livestock Research Institute (ILRI) have found that the numbers of giraffes, hartebeest, impala, warthogs, topis and waterbuck all fell “markedly and persistently” throughout the 580 square mile reserve between 1989 and 2003. They believe increased human settlement around the unfenced park is to blame Photograph: Blaine Harrington III/Corbis

The scientists' sample counts were backed by government population estimates that showed actual losses as high as 95% for giraffes Photograph: Rex Features/Rex Features

The authors of the study, which was funded by the WWF and will be published in the British Journal of Zoology in May, say it presents the most detailed evidence yet on the rapid decline of ungulate, or hoofed, animals in the Mara, in south-western Kenya Photograph: Michael Poliza/Getty Images

The Mara reserve sits at the top of the Mara-Serengeti ecosystem, which hosts the spectacular annual migration of up to 2m wildebeest and other animals Photograph: Arthur Morris/Corbis

An African vulture watches part of a herd of some 1.5m wildebeests as they cross the Mara river during their annual migration Photograph: STAFF/Reuters

A topi with grass and mud on its horns. Topi have suffered a 79% decline in population in the Masai Mara reserve based on aerial counts between 1979 and 2002 Photograph: Arthur Morris/Corbis

The main reason for the population decrease is the rapid expansion of human settlements on the land adjacent to the reserve, scientists say. The area was traditionally used by wild animals for seasonal grazing but is increasingly being turned over to livestock and crop production Photograph: EyesWideOpen/Getty Images

Government population estimates showed losses as high as 80% for warthogs in the period dating back to 1979 Photograph: Gabriela Staebler/Corbis

A lioness hunting warthog in the Masai Mara Photograph: Peter Blackwell/NPL/Rex Features

A lion stretches Photograph: DLILLC/Corbis

An impala with an oxpecker perched on its head. Impala also suffered sharp declines over the 15-year period studied. They were 57% from their 1979 population estimates Photograph: Anup Shah/Getty Images

Impala. Land adjacent to the reserve which was traditionally used by wild animals for seasonal grazing is increasingly being turned over to livestock and crop production Photograph: Art Wolfe/Getty Images

A cheetah chases a female impala Photograph: Federico Veronesi/Getty Images

Numbers of waterbuck have also fallen Photograph: Winfried Wisniewski/ Winfried Wisniewski/zefa/Corbis

The Maasai Mara National Reserve, Kenya Photograph: Robert Harding/Rex Features