Hundreds of wildebeest cross the Serengeti Plain of Tanzania during their annual migration in an undated file photo.

More than a million wildebeest undertake an epic trek every year in late summer, as the animals leave their calving grounds in the Serengeti to seek greener pastures in Kenya to the north.

In late September 2007 some 10,000 wildebeest died while attempting to cross Kenya's Mara River during the northernmost leg of this migration route.

The deaths occurred at Kenya's Maasai Mara National Reserve, as the herd was beginning its swing to the east on its way back to the Serengeti. (See a map and video of the wildebeest migration.)

About one percent of the total species population was wiped out in the incident, conservationists reported.

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