Danny Green / Polar bear (Ursus maritimus) cub ready to jump down from pack ice. Svalbard, Norway, April.

Nick Garbutt / Pack of wolves (Canis lupus). Yellowstone National Park, Wyoming, USA. January.

Daniel J. Cox / Gray Wolf (Canis lupus) pack on ridge in winter, Lamar Valley, Yellowstone National Park, Wyoming

Eric Baccega / Pack of Grey wolves (Canis lupus) howling in the snow, captive. Bavarian Forest National Park, Germany, March. Captive.

Wim van den Heever / White tailed sea eagle (Haliaeetus albicilla) feeding on fish on pack ice, Hokkaido, Japan, February.

Steven Kazlowski / Polar bear (Ursus maritimus) young bear rolling around in the snow, on newly formed pack ice during autumn freeze up, Beaufort Sea, off Arctic coast, Alaska

Ben Cranke / Steller's Sea Eagle (Haliaeetus pelagicus) stood on ice floe, Hokkaido, Japan. February.

Tim Fitzharris / Gray Wolf (Canis lupus) pack walking in snow, Montana

Steven Kazlowski / Polar bear (Ursus maritimus) curious young male on the newly frozen pack ice, Beaufort Sea, off the 1002 area of the Arctic National Wildlife Refuge, North Slope, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) 3-year-olds play fighting on newly formed pack ice, Beaufort Sea, off the 1002 area of the Arctic National Wildlife Refuge, North Slope, Alaska

Steven Kazlowski,Steven Kazlowski / Polar bear (Ursus maritimus) juvenile rolling around on newly formed pack ice, Beaufort Sea, off the 1002 area of the Arctic National Wildlife Refuge, North Slope, Alaska

Steven Kazlowski,Steven Kazlowski / Polar bear (Ursus maritimus) 4-5 year-old on pack ice, low angle shot, off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, Beaufort Sea, autumn