Peter Mather / Arctic Fox (Alopex lagopus) feeding on Caribou (Rangifer tarandus) carcass, Brooks Range, Alaska

Peter Mather / Brown Bear (Ursus arctos) looking into Wolverine (Gulo gulo) caching hole for food, North Slope, Alaska

Peter Mather / Muskox (Ovibos moschatus) pair fighting, Dalton Highway, Alaska

Peter Mather / Wolf (Canis lupus) feeding on Caribou (Rangifer tarandus) carcass, North Slope, Alaska

Peter Mather / Arctic Fox (Alopex lagopus) licking lips, Alaska

Peter Mather / Muskox (Ovibos moschatus) pair fighting, Dalton Highway, Alaska

Peter Mather / Moose (Alces alces) pair in winter, Brooks Range, Alaska

Peter Mather / Wolf (Canis lupus) pups at den, in the Brooks Range at the edge of the Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) porcupine herd in winter near Dempster Highway, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) porcupine herd crossing Blow River, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) porcupine herd crossing river valley, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) newborn calf nuzzling mother, of the porcupine herd, Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) mother and newborn calf, of the porcupine herd, Arctic National Wildlife Refuge, Alaska

Peter Mather / Yukon River outside of Dawson City, Yukon, Canada

Peter Mather / River flowing through valley in autumn, Tombstone Mountains, Tombstone Territorial Park, Yukon, Canada

Peter Mather / Lowell Glacier and Alsek Lake, Kluane National Park, Yukon, Canada

Peter Mather / Winding river in boreal forest, Yukon-Charley Rivers National Preserve, Alaska

Peter Mather / Kathleen Lake beneath Kings Throne mountain, Kluane National Park, Yukon, Canada

Peter Mather / Northern lights reflecting in pond, Ogilvie Mountains, northern Yukon, Canada

Peter Mather / Canoe in Chilkat River, southeast Alaska

Peter Mather / Chinook Salmon (Oncorhynchus tshawytscha) female spawning under northern lights in small tributary of Yukon River, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) aerial of the migrating Porcupine herd, crossing river, Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) females and juveniles, from the Porcupine herd, migrating, Arctic National Wildlife Refuge, Alaska

Peter Mather / Arctic Fox (Alopex lagopus) curled up in snow, North Slope, Alaska

Peter Mather / Arctic Wolf (Canis lupus) running in snow, Alaska

Peter Mather / Wolverine (Gulo gulo) in snow, North Slope, Alaska

Peter Mather / Brown Bear (Ursus arctos) emerging from den in early spring, North Slope, Alaska

Peter Mather / Wolverine (Gulo gulo) outside of snow food caching hole, Arctic National Wildlife Refuge, Alaska

Peter Mather / Moose (Alces alces) pair in winter, Alaska

Peter Mather / Limestone mountains at dusk in autumn, Ogilvie Mountains, Yukon, Canada

Peter Mather / Limestone mountains and rainbow in autumn, Ogilvie Mountains, Yukon, Canada

Peter Mather / Limestone mountains in autumn, Ogilvie Mountains, Yukon, Canada

Peter Mather / Chinook Salmon (Oncorhynchus tshawytscha) in river at night with northern lights, Tatchun Creek, Yukon, Canada

Peter Mather / Canada Lynx (Lynx canadensis) kittens in den, Alaska

Peter Mather / Canada Lynx (Lynx canadensis) den in boreal forest, Alaska

Peter Mather / Burned boreal forest along coast, Yukon, Canada

Peter Mather / Wolverine (Gulo gulo) with collar released by biologists in snow, North Slope, Alaska

Peter Mather / Chinook Salmon (Oncorhynchus tshawytscha) group at fish ladder, Yukon, Canada

Peter Mather / Boreal forest along coast, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) group, Porcupine herd, migrating, North Slope, Alaska

Peter Mather / Frozen river and mountains, Brooks Mountains, Arctic National Wildlife Refuge, Alaska

Peter Mather / Bald Eagle (Haliaeetus leucocephalus) standing on Chum Salmon (Oncorhynchus keta) carcass, Haines, Alaska

Peter Mather / Chum Salmon (Oncorhynchus keta) group protecting redds in small creek, Haines, Alaska

Peter Mather / Chum Salmon (Oncorhynchus keta) protecting redds in small stream with duck feeding on eggs, Haines, Alaska

Peter Mather / Coastal plain wetlands, Arctic National Wildlife Refuge, Alaska

Peter Mather / Coastal plain wetlands showing ponds and polygon formations, Arctic National Wildlife Refuge, Alaska

Peter Mather / Wolverine (Gulo gulo) female in live trap to be studied by biologists, North Slope, Alaska

Peter Mather / Wolverine (Gulo gulo) feeding on Caribou (Rangifer tarandus) carcass, Arctic National Wildlife Refuge, Alaska