Sean Gerrity has disappeared. His lanky figure was last spotted striding toward a line of cottonwood and box elders south of the American Prairie Reserve headquarters in rural northeastern Montana. Now he is nowhere to be seen.

"Sean wanders off if he is not nailed down," says Katy Teson, a colleague of his at the American Prairie Reserve. She climbs into a Suburban to look for him along one of the rutted roads that snake across the northern Great Plains. "But he usually comes back with a great story, like the time he found a vesper sparrow nest that none of us would have spotted."

This time, Gerrity hasn't gone far. Teson finds him sheltering from the relentless wind at