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 / Northern lights over trucks on Dalton Highway which is used to service oil fields in Prudhoe Bay, Alaska

Peter Mather / Northern lights over Alyeska Pipeline, which carries oil from oil fields in Prudhoe Bay near the Arctic National Wildlife Refuge, down to Valdez, Alaska

Peter Mather / Oil fields, Deadhorse, Prudhoe Bay, Alaska

Peter Mather / Oil fields, Deadhorse, Prudhoe Bay, Alaska

Peter Mather / King Eider (Somateria spectabilis) flock near buildings, Prudhoe Bay, Alaska

Peter Mather / Oil fields and Sagavanirktok River, Deadhorse, Prudhoe Bay, Alaska

Peter Mather / Caribou (Rangifer tarandus) porcupine herd on mountain side, Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) porcupine herd in grassland, Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) hide being cleaned by Gwichin hunter, Jeffery Peters, Porcupine River, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) Gwichin hunter, Clifton Salu, looking for caribou in winter, Yukon, Canada

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

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

Peter Mather / Caribou (Rangifer tarandus) bull, of the porcupine herd, near Dempster Highway, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) females, of the porcupine herd, at sunset, Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) females, of the porcupine herd, running, Yukon, Canada

Peter Mather / Grizzly Bear (Ursus arctos horribilis) on coastal plain, Arctic National Wildlife Refuge, Alaska

Peter Mather / Grizzly Bear (Ursus arctos horribilis) on coastal plain, Arctic National Wildlife Refuge, Alaska

Peter Mather / Muskox (Ovibos moschatus) female and sub-adults, 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 / Caribou (Rangifer tarandus) calf, of the porcupine herd, Arctic National Wildlife Refuge, Alaska

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

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

Peter Mather / Caribou (Rangifer tarandus) porcupine herd in coastal plain and river, Arctic National Wildlife Refuge, Alaska

Peter Mather / River flowing across coastal plain, Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) porcupine herd in plain and river, Arctic National Wildlife Refuge, Alaska

Peter Mather / Pacific Loon (Gavia pacifica), Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) bull and females, of the porcupine herd, at calving grounds in fog, Arctic National Wildlife Refuge, Alaska

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

Peter Mather / Caribou (Rangifer tarandus) pair, from the central arctic herd, near Dalton Highway, near Arctic National Wildlife Refuge, Alaska

Peter Mather / Muskox (Ovibos moschatus) bulls on coastal plain, Arctic National Wildlife Refuge, Alaska

Peter Mather / Arctic Loon (Gavia arctica) on nest in wetland, Arctic National Wildlife Refuge, Alaska

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

Peter Mather / Slims River flowing into Kluane Lake, Kluane National Park, Yukon, Canada

Peter Mather / Slims River flowing into Kluane Lake, Kluane National Park, Yukon, Canada

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

Peter Mather / Northern lights over Alyeska Pipeline, Prudhoe Bay, Alaska

Peter Mather / Abandoned cabin from the Gold Rush area under night sky with northern lights, Yukon, Canada

Peter Mather / Abandoned cabin from the Gold Rush area under night sky, Yukon, Canada

Peter Mather / Dall's Sheep (Ovis dalli) rams in alpine field, Wind River, northern Yukon, Canada

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

Peter Mather / Chinook Salmon (Oncorhynchus tshawytscha) male and female salmon in holding pen of fish ladder, Yukon River, Yukon, Canada

Peter Mather / Red Fox (Vulpes vulpes) kits play-fighting at their den, Dempster Highway, northern Yukon, Canada

Peter Mather / Red Fox (Vulpes vulpes) kits play-fighting at their den, Dempster Highway, northern Yukon, Canada

Peter Mather / Bald Eagle (Haliaeetus leucocephalus), Yukon River, Yukon, Canada

Peter Mather / Bald Eagle (Haliaeetus leucocephalus) parent with two week old chicks in nest, Yukon River, Yukon, Canada

Peter Mather / Bald Eagle (Haliaeetus leucocephalus) pair on snow-covered Chilkat River shore, with one eagle carrying radio tracking transmitter, Chilkat Bald Eagle Preserve, Alaska

Peter Mather / Dall's Sheep (Ovis dalli) females licking salt off road, Alaska Highway, Kluane National Park, Yukon, Canada

Peter Mather / Arctic Grayling (Thymallus signifer) gathering to spawn in small creek, Yukon, Canada

Peter Mather / European Magpie (Pica Pica) trio feeding on Chum Salmon (Oncorhynchus keta) on snow-covered Chilkat River shore, Chilkat Bald Eagle Preserve, Alaska

Peter Mather / Bald Eagle (Haliaeetus leucocephalus) feeding on Chum Salmon (Oncorhynchus keta) carcass on snow-covered Chilkat River shore, Chilkat Bald Eagle Preserve, Alaska

Peter Mather / Chinook Salmon (Oncorhynchus tshawytscha) alevins recently hatched from eggs, Yukon River, Yukon, Canada

Peter Mather / Chinook Salmon (Oncorhynchus tshawytscha) pair spawning in small tributary of Yukon River, Yukon, Canada

Peter Mather / Brown Bear (Ursus arctos) standing in river in early winter, Kluane River, Yukon, Canada

Peter Mather / Brown Bear (Ursus arctos) along river in early winter, Kluane River, Yukon, Canada

Peter Mather / Brown Bear (Ursus arctos) walking along road in early winter, Kluane River, Yukon, Canada

Peter Mather / Brown Bear (Ursus arctos) mother and cub on log in river, Yukon, Canada

Peter Mather / Brown Bear (Ursus arctos) mother and cub on log in river, Yukon, Canada

Peter Mather / Moose (Alces alces) bull bull crossing Dempster Highway, northern Yukon, Canada

Peter Mather / Coastal plain, which is the calving and nursing grounds of Porcupine caribou herd and is threatened by potential oil and gas development, Arctic National Wildlife Refuge, Alaska

Peter Mather / Aerial of coastal plain, which is the calving and nursing grounds of Porcupine caribou herd and is threatened by potential oil and gas development, Arctic National Wildlife Refuge, Alaska

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

Peter Mather / Caribou (Rangifer tarandus) bull and females, of the Porcupine herd, grazing in fog, Arctic National Wildlife Refuge, Alaska

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

Peter Mather / Caribou (Rangifer tarandus) aerial of the Porcupine herd resting in snow patch, Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) aerial of the Porcupine herd on tundra, Arctic National Wildlife Refuge, Alaska

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

Peter Mather / Caribou (Rangifer tarandus) mother tending newborn calf, from the Porcupine herd, Arctic National Wildlife Refuge, Alaska

Peter Mather / Caribou (Rangifer tarandus) females and male crossing Dempster Highway while migrating to wintering grounds, northern Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) female and males migrating to wintering grounds, northern Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) females and males migrating to wintering grounds, northern Yukon, Canada

Peter Mather / Caribou (Rangifer tarandus) females and juveniles, from the Porcupine herd, migrating, Blow River, Yukon, Canada