10,000 Wildebeest Drown in Migration "Pileup"

Scores of wildebeest lay dead along the banks of the Mara River in Kenya, having washed downstream after a bizarre mass death that occurred early last week. An estimated 10,000 of the animals drowned while attempting to cross the river during an annual migration, wiping out one percent of the total species population. Photograph courtesy Terilyn Lemaire/Mara Conservancy/WildlifeDirect




10,000 Wildebeest Drown in Migration "Pileup"
Blake de Pastino
National Geographic News
October 1, 2007

In a bizarre mishap that conservationists describe as "heartbreaking," an estimated 10,000 wildebeest have drowned while attempting to cross Kenya's Mara River during an annual migration.
The deaths, which occurred over the course of several days last week, are said to account for about one percent of the total species population.
The drownings created a grotesque wildlife pileup, after part of the migrating herd tried to ford the Mara at "a particularly treacherous crossing point," according to Terilyn Lemaire, a conservation worker with the Mara Conservancy who witnessed the incident. (See a photo gallery of the mass drowning.)
The first animals into the river failed to cross and drowned, while others continued to stampede into the water behind them, Lemaire told National Geographic News by email.
"Once they jumped into the water, they were unable to climb up either embankment onto land and, as a result, got swept up by the current and drowned," she said.
Some 2,000 wildebeest drowned at the crossing in a single afternoon, Lemaire estimated.
"There was no unusual flooding at the time, and there seems to be no extraneous circumstances to these deaths," she said.
"The wildebeest merely chose a crossing point that was too steep."
Drowning deaths are not uncommon during the migration, Lemaire added, but her organization has never witnessed fatalities on this scale.
"It is customary every year for the wildebeest to pick a particularly treacherous crossing point and for there to be a significant die-off," she said, "but the number of deaths during these crossings almost never exceeds one thousand."
Fatal Migration
More than a million wildebeest undertake an epic migration every year in late summer, leaving their calving grounds in the Serengeti Plain of Tanzania to seek greener pastures in Kenya to the north.
The animals, also known as gnu, journey some 2,000 total miles (3,200 kilometers) each year, often joined by thousands of zebras and Thomson's gazelles.
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.
Since the drownings, the animals' bodies have washed downriver, beaching on the Mara's muddy banks and getting caught under a nearby bridge, Lemaire wrote on her blog for the nonprofit WildlifeDirect.
The remains formed what she described as "pungent islands of bloated carcasses."
"The crocodiles, storks, and vultures have not had to worry about where to find their next meal," she wrote.
"Those that aren't consumed will be left and will eventually decompose in the water. These thousands of carcasses will undoubtedly affect the health of the water, but to what extent, only time will tell."
Lemaire also declined to speculate, in her email to National Geographic News, on the impact the mass deaths might have on the wildebeests' overall population health.
"I would imagine that such a significant decrease in population would have an effect," she said, "but what that effect would be and to what extent, I cannot say."