certain size and "whippiness." The activity, which I 

 call "horning," reminds me of a boxer working out on 

 a punching bag. The behavior is easily overlooked, 

 though, which may explain why Serengeti ecolo- 

 gists have not taken its impact into account. Yet the 

 effects are plain to see: repeated horning debarks 

 stems, breaks branches, and eventually kills the 

 aboveground part of a tree. Such damage is com- 

 monly mistaken for elephant browsing, though on 

 close inspection the differences are obvious. 



In 1986 I had the chance to look for horning 

 damage in several parks of South Africa and Nami- 

 bia, where wildebeest populations had crashed after 

 fencing prevented their migrations. The signs of 

 horning there were scarce, and I noted that bushes 

 and trees were invading formerly open grassland. In 

 contrast, there was a marked opening up of the 

 Serengeti woodlands in the 1970s and 1980s, as the 

 wildebeest population, finally freed of rinderpest, 

 increased apace. Together with my systematic obser- 

 vations of horning, the demographic data convince 

 me that wildebeests, along with elephants and fire, 

 have had profound environmental effects. That may 

 seem astonishing, but when you consider that in the 

 Serengeti a quarter-million competing bulls have 

 been at it year after year, it seems less incredible. By 

 adding tree-horning to the better-known effects of 



feeding, trampling, and depositing manure, it be- 

 comes clear that this antelope actively creates and 

 helps maintain the kind of habitat that it needs. 



At the same time, the areas available for grazing 

 and access to water determine the size of the 

 Serengeti wildebeest population. The equilibrium 

 varies from year to year, depending on rainfall and on 

 how much grass is produced. When there is not 

 enough food, the weakest members of the population 

 starve. In the absence of the occasional severe drought, 

 most of the culling occurs late in the dry season, when 

 the calves, whose nutritional needs for growth put 

 them at particular risk, are most likely to lose condi- 

 tion and eventually succumb to parasites and disease. 

 Those factors imply that despite its success, the west- 

 ern white-bearded wildebeest remains vulnerable. 



Then there are the pressures of human develop- 

 ment.The Serengeti wildebeests' access to LakeVic- 

 toria, only a mile or so from the western boundary 

 of Serengeti National Park, was cut off years ago by 

 lakeside settlement. How long canTanzanian politi- 

 cians resist the demands of the burgeoning human 

 population for further expansion? Other threats are 

 building in Kenya, even in the Masai Mara National 

 Reserve, where most of the Serengeti wildebeest 

 population ends up during the dry season. 



Fortunately, the Kenyan government 

 has put an indefinite hold on a hydro- 

 electric scheme to divert a major tributary 

 of the Mara River. Still, the energy pro- 

 ject is not dead. Even more serious is the 

 threat posed by the destruction of the Mau 

 Forest, the catchment for the Mara River 

 and other rivers. Illegal invasion of the for- 

 est by settlers is continuing apace. Tree- 

 cutting, clearing, and farming have already 

 diminished the flow of the Mara. Soil ero- 

 sion is muddying the water and interfer- 

 ing with subsistence fishing. According to 

 a study by the World Wildlife Fund, phos- 

 phates and nitrates in the river have al- 

 ready reached environmentally harmful 

 concentrations. All those unfortunate de- 

 velopments are taking place against a 

 background of global climate change that 

 is creating an increasingly arid climate in 

 East Africa. 



If wildebeests could speak for them- 

 selves, I have no doubt that they would de- 

 cry these developments. Since the animals 

 are unable to, only we can speak out for 

 their interests — and convince our fellow- 

 human beings that their interests are ulti- 

 mately our own. □ 



September 2006 NAI URAI HISTORY 



35 



