Dr. Steven Amstrup spent years plowing through unexplored frontiers of polar bear research in the Arctic. Amstrup, of Kettle Falls, Wash., was the first person to succeed in putting radio collars on Alaskan polar bears, leading to his discovery that more than half the mother bears den on drifting chunks of ice. The finding portended disaster for the future of the species, as rising temperatures threaten their survival, he said.