1. Gates of the Arctic National Park and Preserve, Arctic Inventory and Monitoring Network, National Park Service , 4175 Geist Road, Fairbanks, Alaska, 99709, USA
2. Salt Spring Island , British Columbia V8K 1V1 Canada
3. Département de biologie, Caribou Ungava & Centre d’études nordiques , Université Laval , Québec (QC), G1V 0A6 , Canada
4. Norwegian Institute for Nature Research (NINA) , Høgskoleringen 9, NO-7034 Trondheim , Norway
5. Department of Environment and Natural Resources, Government of the Northwest Territories , Yellowknife, Northwest Territories , Canada
6. Fish and Wildlife Branch, Environment Yukon, Yukon Government , Dawson City , Yukon , Canada
7. Department of Biology , University of Maryland , College Park, Maryland, 20742, USA , and Department of Environmental and Forest Biology, SUNY College of Environmental Science and Forestry , Syracuse , NY 13210