East (1999) estimated the population size of Thomson's Gazelle at around 550,000 animals. The migratory population of the Serengeti ecosystem, which is Africa?s largest and most spectacular gazelle population, has been estimated at 174,015 (± 37,406 S.E.), based on data from the 2003 wet season (Mduma 2003), which is indicative of a steep decline since the estimate of 500,000 in the early 1980s (Sinclair and Norton-Griffths 1982). This would be consistent with a loss of large wild herbivores in the Masai Mara ecosystem in Kenya, where there are estimated to be ca. 40,000 in the Masai Mara reserve, a decline from ca. 100,000 in 1977 (Ottichilo et al. 2000). Likewise, Estes et al. (2006) report a decline of 60% from 1978-2005 in the Ngorongoro Crater. There are also reports of declines in the Ewaso Nyira basin, where numbers were estimated at ca. 33,000 in 1977, but at one-third of this in 1997 (Muchoki 2000).
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