KARSTEN HEUER is a wildlife biologist and park warden who has worked in Banff and Jasper national parks in the Rockies, in Inuvik in Canada's far north, in Slovakia and Poland, and in the Madikwe Game Reserve in South Africa. A recipient of the Wilburforce Foundation Conservation Leadership Award, he has spent much of the past decade following some of North America's most endangered wildlife on foot and skis. In 1998 and 1999 he walked and skied from Yellowstone National Park, Wyoming to Canada's Yukon Territory to highlight a proposal for a 1,900-miles-long system of wildlife corridors and core reserves (the Y2Y Conservation Initiative). He chronicles this adventure in Walking the Big Wild: From Yellowstone to Yukon on the Grizzly Bear's Trail. In 2003, he again set off on skis and foot with his wife, Leanne Allison, and over the course of five months, followed the Porcupine Caribou Herd from their Yukon winter range to their endangered Alaskan calving grounds and back. This is the subject of Being Caribou, both his book and the accompanying National Film Board of Canada documentary.