Matt Walker BBC Nature 31 May 11;
Populations of wildlife species in the world-renowned Masai Mara reserve in Kenya have crashed in the past three decades, according to research published in the Journal of Zoology.
Numbers of impala, warthog, giraffe, topi and Coke's hartebeest have declined by over 70%, say scientists.
Even fewer survive beyond the reserve in the wider Mara, where buffalo and wild dogs have all but disappeared, while huge numbers of wildebeest no longer pass through the region on their epic migration.
However, numbers of cattle grazing in the reserve have increased by more than 1100% per cent, although it is illegal for them to so do.
This explosion in the numbers of domestic livestock grazing in the Mara region of south-west Kenya, including within the Masai Mara national reserve, is one of the principal reasons wildlife has disappeared, say the scientists who conducted the research.
Dr Joseph Ogutu, a senior statistician in the Bioinformatics unit of the University of Hohenheim, Germany conducted the study with colleagues there and at the International Livestock Research Institute in Nairobi, Kenya.
They already knew that populations of some large mammals were declining in the Masai Mara, based on an earlier study published in 2009.
But this only examined seven species, over a 15 year period, using limited sampling techniques.
So to get a fuller picture, the team looked at data gathered since aerial monitoring of Kenya's wildlife began in 1977.
This covered 12 species of large mammal, ostriches and livestock, and allowed the team to calculate trends in wildlife numbers over a 33-year period across the entire reserve, and in the Masai pastoral ranches adjoining the reserve.
The data also allowed the scientists to investigate whether numbers of migratory wildebeest and zebra coming into the Mara each year have reduced.
"We were very surprised by what we found," Dr Ogutu told the BBC.
"The Mara has lost more than two thirds of its wildlife."
Of the 13 large species studied, only ostriches and elephants had not fared badly outside of the reserve, while inside the Masai Mara only eland, Grant's gazelle and ostrich showed any signs of population recovery in the past decade.
The declines are particularly surprising, say the scientists, as they had expected animal populations to have recovered since 2000-2001.
That is when major conservancy efforts, and an increase in local policing, began in an attempt to protect the wildlife there.
"But to our great surprise, the extreme wildlife declines have continued unabated in the Mara," says Dr Ogutu.
"The great wildebeest migration now involves 64% fewer animals than it did in the early 1980s," he adds.
That is despite numbers of wildebeest on the Serengeti, where the migratory animals that cross the Mara come from, staying relatively unchanged.
During the wet season, when there is no migration, resident wildebeest in the reserve have all but disappeared, falling by 97%.
Zebra numbers residing inside the reserve have also fallen by three-quarters.
There appear to be three main causes of these dramatic declines: the activities of poachers, changing land use patterns in ranches within the Mara, and an increase in the number and range of livestock held on these ranches.
According to Dr Ogutu, over 1500 poachers have been arrested within the Mara conservancy between 2001 and 2010, with more than 17,300 snares collected by rangers in the same period.
"Poaching continues to be a major menace," he says.
But the boon in livestock numbers can be just as damaging.
"Not only have numbers of cattle, sheep and goats increased but their distribution has widened, with the density of cattle increasing more than three-fold and that of sheep and goats more than seven fold up to 5km inside the reserve.
"Sadly though, wildlife distribution has contracted throughout the entire Mara region in the same period."
Heavy grazing by these livestock is thought to be displacing the natural fauna.
It may also be making the larger species more vulnerable to starvation during the recurrent severe droughts that have struck the Mara in recent decades.
This competition may be what has already driven out the buffalo, say the scientists.
The expansion of settlements, fences and livestock numbers need to be regulated if these declines in wildlife are to be arrested, they propose, as well as bringing down poaching levels.
"Otherwise, the status of Masai Mara as a prime conservation area and premier tourist draw card in Kenya may soon be in jeopardy," says Dr Ogutu.
