Danny Green / Reindeer (Rangifer tarandus), two standing on ridge in snow. Svalbard, Norway, April.

Danny Green / Reindeer (Rangifer tarandus) hunkering down in snow during blizzard. Svalbard, Norway, April.

Danny Green / Reindeer (Rangifer tarandus) walking in snow. Svalbard, Norway, April.

Danny Green / Polar bear (Ursus maritimus) sleeping in snow. Churchill, Manitoba, Canada, November.

Danny Green / Arctic fox (Alopex lagopus) following scent, in winter pelage. Svalbard, Norway. April.

Danny Green / Arctic fox (Alopex lagopus) camouflaged in winter pelage. Svalbard, Norway, April.

Danny Green / Arctic fox (Alopex lagopus) in snow. Svalbard, Norway. April.

Danny Green / Ringed seal (Pusa hispida) resting on ice, reflected in water. Svalbard, Norway. July.

Nick Garbutt / King penguin (Aptenodytes patagonicus), two sleeping on snow. Grytviken, South Georgia. March.

Ann & Steve Toon / Cheetah (Acinonyx jubatus) walking, silhouetted at dusk. Zimanga private game reserve, KwaZulu-Natal, South Africa.

Ann & Steve Toon / African elephants (Loxodonta africana) herd silhouetted at sunset. Chobe National Park, Botswana.

Oscar Dewhurst / Mute swan (Cygnus olor), two cygnets sheltering under parent's wing. Richmond Park, London, England, UK. April.