SALMON, Idaho — A record number of big-game animals perished this winter in parts of Montana, Idaho and Wyoming from a harsh season of unusually heavy snows and sustained cold in the Northern Rockies, state wildlife managers say.

"Elk, deer and moose -- those animals are having a pretty tough time," said Wyoming Game and Fish biologist Doug Brimeyer.

Snow and frigid temperatures in pockets of Idaho, Montana and Wyoming arrived earlier and lingered longer than usual, extending the time that wildlife were forced to forage on low reserves for scarce food, leading more of them to starve.

Based on aerial surveys of big-game herds and signals from radio-collared animals, experts are documenting high mortality among offspring of mule deer, white-tailed deer and pronghorn antelope.

This comes as big-game animals enter the last stretch of a period from mid-March through early May that is considered critical for survival.

Wildlife managers estimate die-offs in the tens of thousands across thousands of square miles that span prairie in northeastern Montana, the upper Snake River basin in Idaho near Yellowstone National Park and the high country of northwestern Wyoming near the exclusive resort of Jackson.

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