The Drought of 2009

by Dr. David Western

 Amboseli, Kenya, December 4, 2009 ~ Drought has taken a devastating toll of Amboseli’s wildlife in the last few months.  Nearly 15,000 animals have died of starvation since early this year. Wildebeest numbers fell from over 6,000 to fewer than 150, zebra from some 7.000 to 1,500 and buffalo from 600 to 185. Large numbers of elephant and many hippos have also died. Most of those losses occurred the three months between September and November. The proportional losses are among the biggest recorded anywhere in recent times. 

Background to the Drought

The 2009 drought was triggered by poor rains throughout 2008 and a total failure of the long rains in April and May this year. By June, pastures were grazed down throughout the Amboseli region. The Maasai, realizing the severity of drought, moved their cattle herds as far as Nairobi, Naivasha and the coast in Kenya, and into neighboring Tanzania. Despite the huge exodus in search of pasture, questionnaire surveys conducted by the African Conservation Center and ACP put the cattle losses among pastoralists in the region at 75% or more.

(For a full account of the human tragedy nationwide, click here).

Wildlife in the Amboseli region concentrated on the swamps in and around the national park as the drought worsened. By July our aerial counts and ground surveys indicated that a heavy loss of wildlife was likely in the coming months. The swamp sedges were heavily grazed and buffalo were feeding belly-deep in water in search of forage. Elephants had begun leaving the park in growing numbers. By August, we recorded the first wildebeest deaths, mainly among young animals. By September, wildebeest and zebra were grazing deep into the swamps in search of forage, something not seen in Amboseli before. Many wildebeest were weak and dying of starvation. Deaths among zebra and buffalo were still relatively few, but growing.

In early October, the death count grew rapidly. Our monthly counting plots were far too few and scattered to track and map the carcasses, leading us to set up a series of counting plots in and around the swamps where the herds and carcasses were concentrated. David Maitumo completed the first counts by October 5th. Our estimates put the number of dead wildebeest at close to 2,000, zebra at close to 1,000, and buffalo at over 100. 

After October 5, the deaths mounted at an alarming rate. By mid-October the wildebeest population was in free-fall and zebra and buffalo deaths were mounting quickly. By late October, over 50 wildebeest and 40 zebra were dying each day. Hippos were weak and dying, but too deep in the swamps to count. We counted more than 20 dead elephants in and around the swamps.  (Image Gallery, here.)

The scale and speed of collapse in the wildebeest and zebra herds in late October and November is hard to grasp. David counted over 90 carcasses in a 300 meter radius plot at the edge of the Longinye Swamp in early November. By then, 100 wildebeest and over 50 zebra were dying each day. By mid-November all the wildebeest and zebra along the green fringe of seasonal Lake Amboseli had died and fewer than one hundred remained in Longinye Swamp where thousands had clustered two months earlier. The figures are summarized in the following graphs (click on charts for larger view):

(Click on charts for larger view)

It was evident that the swamp pastures would begin to grow back once the herbivore populations dropped to the point where grazing pressure could no longer suppress growth. But recovery was severely retarded, perhaps due to the extremely heavy grazing the grasses and sedges had sustained, but also because recharge from Kilimanjaro fell with the prolonged drought. 

In early November I met with Cynthia Moss, director of the Amboseli Elephant Project, to discuss the crisis. Nothing in our decades of study in Amboseli came close to the wildlife carnage. We agreed that the population declines of wildebeest and buffalo were so steep that both species risked dropping to unrecoverable levels. 

ACP reported the crisis to the director of Kenya Wildlife Service on November 19th. On November 23rd the director authorized the African Conservation Centre and ACP to work with KWS staff in delivering emergency food stocks to the remaining wildebeest and buffalo. 

I completed a final aerial and ground survey before the three trucks carrying hay, molasses and survival pellets reached Amboseli on 25th November. In a remarkable turnaround in 5 days, the swamp sedges and swamp-edge grasses were finally breaking through and the remaining zebra and buffalo were eating non-stop on the new growth. On meeting up with the Kenya Wildlife Service Assistant Warden, veterinarian, Dr. Ndere and Cynthia Moss next day, we decided there was no longer any call for feeding, given the abundance of fresh grass.    

Cause of Population Decline

The causes of the mass mortality in Amboseli stem from a long-term decline in habitat diversity, a build-up in grazing animals, the steady depletion of swamp grazing, a severe shortage of rain in 2008, and the failure of the long rains in 2009. Details of the long term changes leading to a loss of species diversity and increasing risk of drought are detailed in “The Ecology and Changes of the Amboseli Ecosystem. Recommendations for Planning and Conservation. David Western, 2007.” (Click here to download this report as a PDF) 

The loss of woodlands in Amboseli during the 1960s and 1970s led to the expansion of grasslands and swamps, a steep decline in browsing species, especially impala and giraffe, and a sharp increases in grazers, notably wildebeest, zebra and buffalo. The steady build-up in resident elephant herds in the park following heavy poaching in the 1970s gradually opened up the bushy perimeter of the swamps, further increasing the numbers of grazers. By the 1990s, the grazing pressure on the swamps had reduced the tall sedges to shorter pasture, causing a steady loss of reserve forage during droughts. The loss of swamp pasture was temporarily reversed by the extreme rains and floods of the 1998 El Niño but continued to fall after 2000. 

The collapse of the wildebeest, zebra, and buffalo herds in the last few months can be attributed to a culmination of the long-term loss of habitat and pasture decline, triggered by a two years of extreme drought.

The Repercussions

Despite the recovery of swamp grazing at the end of November, the fallout from the 2009 drought is far from over. 

The wildebeest numbers have fallen so low that the species is in danger of extinction in Amboseli. No calves are likely to be born within a year and the predation pressure will be severe. Hyena and lion populations have grown steadily in Amboseli in recent years and have enjoyed a surfeit of prey as the herbivores concentrated around the swamp in the drought. Within a few weeks, the impact of the population crash in wildebeest and zebra will be felt by the large carnivores. Competition between the 50 or so lions and 250 hyenas is likely to be acute in the coming weeks. The consequences could be especially grave for the lion, a species facing severe threats across Africa. 

Another immediate concern is a sharp rise in livestock attacks by hyenas and lions as the Maasai return to the Amboseli with rains. The devastation of the pastoralists' herds in recent months puts them in dire straits and in no mood to tolerate losses to predators. 

The transfer of the drought losses among herbivores to the carnivore population will need to be closely monitored in the next few months to anticipate the consequences as soon as possible.

The fallout of the drought will mount as the impact of the population slump is felt throughout and beyond Amboseli. The viewing attraction of Amboseli will be greatly diminished and could see a sharp fall in wildlife revenues to the park and Amboseli communities. 

In the longer term, the large drop in wildlife and livestock numbers in Amboseli this year gives a window of opportunity for restoring the degraded pastures and habitats of the area, for rebuilding ecological and social resilience to drought, and for conserving the park and ecosystem more effectively than in the last few decades. 

Facing up to the Challenges: The Next Steps

The collapse of the herbivore populations in Amboseli poses enormous challenges and calls for hard decisions.

The Kenya Wildlife Service and Maasai community (led by the newly created Amboseli Ecosystem Trust) are meeting the safari industry, resident researchers, and non-government organizations in Amboseli on December 9th to take stock of the drought and the challenges ahead. ACC will fund the meeting. 

A fuller report of its finding on the drought will be posted on the ACP website shortly, together with further developments in Amboseli.   

<-- Back to Drought Page (overview) 

<-- Back to Amboseli Ecosystem Page