AP in Istanbul, via The Guardian, reports:

First one sheep jumped to its death. Then stunned Turkish shepherds, who had left the herd to graze while they had breakfast, watched as nearly 1,500 others followed, each leaping off the same cliff, Turkish media reported yesterday.
In the end, 450 animals died, the daily newspaper Aksam said.

Those which jumped later were saved as the pile got higher, cushioning the fall.

“There’s nothing we can do. They’re all wasted,” Nevzat Bayhan, a member of one of 26 families whose sheep were grazing together in the herd, told Aksam. The estimated loss to families in the town of Gevas, located in Van province in eastern Turkey, is about 100bn Turkish lira (£43,000), a significant amount in a country where average GDP per person is around £1,550.