The restocking of wildlife numbers in Amboseli after the drought of 2009 was given an initial boost by the immigration of wildebeest and zebra from adjacent populations. The dry season following the drought, which left fewer than 300 wildebeest and 2,600 zebra out of the 7,000 or so starting numbers for each species, saw an influx of some 1,400 wildebeest and several hundred zebra from adjacent populations, most likely Tsavo and northern Tanzania.

By late 2010, wildebeest numbers in Amboseli peaked at 1,400 and zebra at 2,700. Following the migrations out of Amboseli with the November-December rains, we expected to see larger numbers return following the birth season. As explained in the last report the unseasonal cyclone rains across the region kept the wildebeest and zebra populations out of the park and basin. Aerial counts of the park in February, the time of peak population numbers in previous years, showed the lowest wildlife numbers recorded in over 40 years. Wildebeest numbers dropped to 10 and zebra 71. Buffalo numbers fell from over 200 to 90. The extended migration lead to low populations in the park from November of 2010 to the dry season beginning late May of 2011, which put further pressure on the carnivore populations resulting in continued attacks on livestock by hyenas and lions.

The eventual return of the migrations in June, seven months since its start, should have raised wildebeest and zebra numbers following the birth season. The first births in wildebeest and zebra after the drought occurred at the end of 2010 and early 2011, indicating that wildebeest and zebra took 3 months or more to recover before conceiving. We anticipated a 20 percent or more boost to the populations due to post-drought births.

Surprisingly, the aerial and ground counts ACP conducted in July and August show the zebra population down this dry season, rather than up as expected. Zebra numbers fell from the 2010 peak of 2,700 to 1,800, despite the birth recruitment (Figure…..). The lower figure suggests that many zebra moved to other areas rather than return to the basin. Wildebeest populations remained about the same as 2010 (Fig..). A further 150 animals were counted close to the basin, giving a total of 1,550 compared to a peak of 1400 in 2010. This is a lower figure than the 1800 or so expected after the birth season, suggesting either a poor recruitment, heavy predation or fewer animals returning to basin.

The picture for buffalo shows a somewhat downward dip in the population for the August dry season, from 210 at a peak in 2010 pre-birthing population, to some 185. Given that buffalo are relatively resident in the basin and environs, the indications are that the population has decline despite the post-drought birthing.

The rains for the first half of 2011 were nearly as poor as the rains for the same period in 2009. FEWSNET, the early warning systems that predicted extreme droughts in the Horn of Africa this year, also predicted extreme droughts in the Amboseli region. This prediction, based largely on rainfall deficit, did not take account of the sharp fall off of grazing pressure following 2009 and so gave an erroneous prediction. In reality, the low herbivore populations in the basin due to the drought and the following extended migrations due to unseasonal rains in January, left abundant pasture in and around Amboseli. The condition of wildlife and livestock is good, despite the poor rains. A good amount of surplus grazing remains to the north of Amboseli, and swamp-edge pastures in the basin have barely been grazed since November of 2010. The Cynodon grasslands along the edge of Lake Amboseli that have supported large herbivore populations every dry season since the 1960s, are devoid of herbivores and support a dense matt of vegetation.

The surplus grazing in Amboseli has spurred a rapid growth in sheep and goat herds among Maasai to make up for the collapse of the cattle herds in the 2009 drought. Numbers are up by a third since the drought, shifting the pastoral economy to a far heavier dependence on small stock than ever before. We expected a sluggish growth in cattle herds because of their longer gestation and slower growth rate, but did not reckon with the long distance restocking arising out of the emaciated herds in northern Kenya and Somalia. The good condition of cattle in Amboseli due to surplus grazing and the poor condition of the northern cattle and poverty caused by the extreme drought in the Horn has worked to the advantage of southern herders.

Maasai in the Amboseli region have been selling their healthy cattle and buying up northern Kenya and Somali cattle at half the price. The 2:1 price advantage, the surplus grazing in Amboseli and the services of long-distance truckers and traders, is allowing the southern Maasai to restock their herds far faster than expected.

There are three important points emerging from the ongoing ACP monitoring in the Amboseli Basin and across the ecosystem that reinforce the post-drought picture given in earlier reports.

First, events driving the collapse of the herbivore populations in Amboseli and the rising carnivore-human conflict must be considered broadly. The prey shortages faced by lions and hyenas has been deepened by the unseasonal rains in January, the prolonged migration of herbivores and the poorer-than-expected numbers of wildlife in the August dry season. The behavior of the herbivores in response to higher predation risk appears to have a strong influence on their use of the basin and daily movement patterns in and out of the park.

Second, the continued pressure on swamps and woodlands due to heavy use of the park by elephants will slow the recovery of habitats and drought grazing areas. This intensive use calls for an accelerated development of elephant exclosures to protect plant refugia and seed banks.

Finally, close attention must be paid to the shifting social and economic patterns of pastoralism and large-scale movements of livestock into and out of the regions as a result of drought evasion, and to the new drought recovery strategies of trading fewer healthy cattle for drought-weakened animals from the north. The large-scale movements of cattle into and out of the Amboseli ecosystem reduces the impact on pastures during droughts on the one hand, but slows post-drought recovery of pastures on the other.

Based on the long-term findings of ACP, David Western wrote a review of causes and implications of deepening drought in the pastoral areas of Kenya (reference to SciDev.Net). ACP staff have been attending emergency meetings called by the African Union and International Livestock Research Institute to discuss the worsening drought conditions in the Horn of Africa.

The Amboseli Ecosystem Management Plan (cross reference) is due for a 5-year review shortly. ACP will urge that the plan be reviewed in light of the drought and that heavy emphasis be put on recovery plans that address the underlying causes of habitat and species loss and the ecological dislocations aggravating human-wildlife conflict.