Continuing signs of recovery for Amboseli

Amboseli continues to recover from the devastation of the 2009 drought.  In this update we describe some of the highlights of Amboseli’s road to recovery and identify the persistent challenges facing the ecosystem. 

To document the impact of the drought on livestock and wildlife across the Amboseli ecosystem, the Amboseli Conservation Program (ACP) conducted a aerial count of the Ilkisongo and eastern Kajiado area (count report PDF).  Using standard sampling methodologies, this count represents the most recent in a long history of counts of the ecosystem conducted by ACP since 1973 and DRSRS since 1977 (Department of Resource Surveys and Remote Sensing) (DRSRS).  Details of past counts and long term population trends are described elsewhere (Ecology and Changes in Amboseli). 

A comparison of the pre- and post-drought aerial counts gives an estimated loss of 92% of wildebeest and 86% loss of zebra.  These estimates for the Amboseli ecosystem corroborate the losses estimated on ground counts of the Amboseli basin during the 2009 drought (Carcass counts).  The ground counts showed a 93% loss of wildebeest and a 65% decline in both zebra and buffalo.  A detailed report on the results of the February count and an assessment of recent population changes resulting from the 2009 drought has been posted on the ACP website (count report PDF).     

The Kenya Wildlife Service (KWS) and other organizations conducted an aerial total count of the Greater Amboseli and adjoining ecosystems either side of the Kenya-Tanzania border in early March (KWS report).  The KWS total counts give an estimated loss of 83% of wildebeest and 71% loss of zebra and 63% loss of buffalo compared to a similar pre-drought count flown in 2007.  The broad agreement between the different counts emphasizes the severe impact of the 2009 drought, and highlights the need for continued monitoring to track recovery and assess long term vulnerability of different species and the ecosystem as a whole.

The KWS count, which was conducted almost a month after the ACP count, shows that wildebeest and zebra from neighboring areas, most likely Tsavo West and Kaputei, moved into the dispersal area of the ecosystem with the heavy rains of early 2010.  At the end of the drought in November 2009, total counts in the Amboseli basin show that only some 312 wildebeest and 1828 zebra survived. Large losses were also reported from neighbouring dry season populations, including Kimana and Chyulu.

Counts of zebra and wildebeest in the Amboseli basin conducted since the migrants began returning after the rains show that some immigration of wildebeest has occurred from adjacent ecosystems.  In early July, ACP conducted an aerial total count of wildebeest and zebra across the Amboseli Basin.  We recorded 1667 wildebeest and 1724 zebra in the Amboseli basin area, with 40% of wildebeest and 56% of zebra occurring in the national park. The counts show that some 1300 or so wildebeest have moved into Amboseli from adjacent populations. There does not, as yet, seem to be any influx of zebra.

The immigration of over 1,300 wildebeest is good news for Amboseli. It means that there is no immediate call for translocation to ensure the survival of the Amboseli population. The herd should be sufficient to withstand the predation expected this dry season, especially considering the lion population is down by over a third since December 2009 (see below).

It is not clear yet where the immigrating wildebeest came from, but the various indications and past counts point to the wet season dispersing herds moving out of Tsavo and perhaps northern Tanzania. The immigrant animals are somewhat smaller and darker than the Amboseli wildebeest. We aim to trace their origins more rigorously through genetic and mineralogical studies.

The natural restocking of the Amboseli populations underscores the importance of maintaining connectivity between Amboseli and adjacent ecosystems. Had the connections been severed, the Amboseli population would likely have been too low to recover, given the high predation pressure in the basin. The connection between Amboseli and Tsavo through Mbirikani is presently under threat of development along the Loitokitok-Emali Road, which has recently been upgraded to a bitumen surface.

While recent immigration has reduced the immediate threat of a local population collapse, it is still too early to gauge how many animals will stay in Amboseli, or the implications of population declines for carnivores and livestock depredation.  A large portion of the wildlife herds are moving out of the basin each evening, perhaps due to their low numbers and heavy predation pressure.  Hyena populations appear healthy and there are numerous pups and pregnant females.  Predation by hyenas on wildlife and livestock fell sharply with the rains. Observations point to hyenas living off the 10,000+ carcasses left by the drought. Few carcasses now remain and there have been reports of an increase in hyena attacks on livestock in recent weeks. 

In contrast to hyenas, lions suffered acute food shortage with the onset of the rains. As reported previously (LINK), lion predation on livestock increased steeply after the collapse of wildebeest and zebra populations and their dispersal with the rains.  Despite the early warnings ACP gave in December (LINK to meeting report), there was insufficient coordination and effort to prevent high levels of livestock depredation and reprisals from Maasai.  As a result, a minimum of 19 lions have been killed in the ecosystem. 

Human-lion conflict has eased off recently with the return of many of the large herbivores to the basin, but the community remains hostile to lions because of the weak preventative measures. Far more effort to prevent lion attacks is needed to avoid further loss of livestock and reprisals on large carnivores.

The vegetation in Amboseli has recovered quickly from drought due to the heavy and prolonged rains since December and the low grazing pressure.  Herbaceous plant cover on the plains is higher than it has been in years and is reminiscent of the post drought period of the 1970s.  Fever tree seedlings are abundant along the edges of the swamps, and the swamps themselves are beginning to recover from the intense grazing pressure during the drought.  Although the Amboseli elephant herd declined during the drought, the number in the Park rose steeply with the rains. The influx will prevent the maturation of the new crop of fever tree seedlings and the recovery of the tall sedges over much of the swamp.

The good rains and low grazing pressure in Amboseli present a good opportunity to rebuild Amboseli’s habitat diversity and resilience. KWS has strongly endorsed the need for woodland and swamp restoration plots recommended by the Amboseli Ecosystem Plan. ACP has partnered with Cheli and Peacock to rebuild the Ilmarishari restoration plot and the exclosure is close to completion. KWS has similar plans to establish several other restoration plots across the national park.     

The uncertainties over the numbers of wildlife returning to Amboseli National Park, the intense predation pressure and consequences for both wildlife and livestock, and the opportunity for large scale habitat restoration call for intensified monitoring throughout this dry season.  ACP will continue its monitoring program and work closely with KWS and other agencies to ensure sufficient coverage and regular reporting to both the warden and the local communities.  Please check here for ongoing updates on the situation in Amboseli including results from the integrated monitoring program.