Steven Kazlowski / Polar bear (Ursus maritimus) sow with spring cub feeds on "sugar snow" or the ice crystals formed on top of the snow, essentially taking a drink of water, outside their den. Winter, arctic coast of Al...

Steven Kazlowski / Polar bear (Ursus maritimus) sow hunting for seals amidst the sea ice floating off the coast of Svalbard, Arctic.

Steven Kazlowski / Polar bear (Ursus maritimus) sow hunting for seals on sea ice floating off the coast of Svalbard, Arctic

Steven Kazlowski / Female polar bear (Ursus maritimus) hunting for seals amidst the sea ice floating off the coast of Svalbard, in summer, Norway

Steven Kazlowski / Female Polar bear (Ursus maritimus) curiously checks out the sailboat and photographer, standing upright on hind legs, Svalbard, Norway. August 2009

Steven Kazlowski / Female Polar bear (Ursus maritimus) curiously checks out the sailboat and photographer, standing upright on hind legs, Svalbard, Norway. August 2009

Steven Kazlowski / Female Polar bear (Ursus maritimus) hunting seals on the sea ice, stops to check out the sailboat and photographer, standing upright on hind legs, Svalbard, Norway. August 2009

Steven Kazlowski / Portrait of Polar bear (Ursus maritimus) sow walking with her newly emerged cub, acclimatising on the snow in late winter, Arctic coast of Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow walking with her newly emerged cub, acclimatising on the snow in late winter, Arctic coast of Alaska

Steven Kazlowski / Portrait of Polar bear (Ursus maritimus) sow walking with her newly emerged cub, acclimatising on the snow in late winter, Arctic coast of Alaska

Steven Kazlowski / Portrait of Polar bear (Ursus maritimus) sow with her cub outside their den in late winter, Arctic coast of Alaska

Steven Kazlowski / Portrait of Polar bear (Ursus maritimus) sow playing with her cub outside their den in late winter, Arctic coast of Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow playing with her cub outside their den in late winter, Arctic coast of Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with cub sleeping outside their den in winter, Arctic coast of Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with cub drinking ice crystals formed on top of the snow, outside their den in winter, Arctic coast of Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow walking over snow with her spring cub outside their den in late winter, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow plays with her spring cub outside their den in late winter, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow plays with her spring cub outside their den in late winter, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with spring cub, newly emerged from their den in late winter, Arctic coast, Alaska, USA

Steven Kazlowski / Polar bear (Ursus maritimus) sow with spring cub, newly emerged from their den in late winter, Arctic coast, Alaska, USA

Donald M. Jones / Wild Boar (Sus scrofa) sow with piglets, central Florida

Donald M. Jones / Wild Boar (Sus scrofa) sow, central Florida

Steven Kazlowski / Rear view of Polar bear (Ursus maritimus) sow hunting for seals on sea ice, off the Svalbard coast, Norway, August 2009

Steven Kazlowski / Polar bear (Ursus maritimus) sow hunting for seals on sea ice, off the Svalbard coast, Norway, August 2009

Steven Kazlowski / Polar bear (Ursus maritimus) sow hunting for seals on sea ice floating off the Svalbard coast, Norway, Summer

Steven Kazlowski / Polar bear (Ursus maritimus) sow on sea ice hunting for seals, off the coast of Svalbard, Norway

Steven Kazlowski / Polar bear (Ursus maritimus) sow and cub resting, on an island along the Svalbard coast, Norway

Steven Kazlowski / Polar bear (Ursus maritimus) sow hunting for seals on ice, off the Svalbard coast, Norway

Steven Kazlowski / Polar bear (Ursus maritimus) sow curled up on ice resting from hunting with a seal in the distance, Svalbard, Norway, August 2009

Michael Quinton / Grizzly Bear (Ursus arctos horribilis) sow, Alaska

Michael Quinton / Grizzly Bear (Ursus arctos horribilis) sow, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) collared adult sow plays with her spring cub on pack ice, Arctic coast, 1002 area of the Arctic National Wildlife Refuge, Beaufort Sea, Alaska, October 2008

Steven Kazlowski / Polar bear (Ursus maritimus) collared sow uses its extra sharp nose to looks for food along the Arctic coast, early autumn, 1002 area of the Arctic National Wildlife Refuge, Alaska, October 2008

Steven Kazlowski / Polar bear (Ursus maritimus) sow with two cubs rest on newly formed pack ice, early autumn, 1002 area of the Arctic National Wildlife Refuge, Arctic coast, Beaufort Sea, Alaska, October 2008

Steven Kazlowski / Polar bear (Ursus maritimus) collared sow nurses her spring cub out on the pack ice along the Arctic coast, 1002 area of the Arctic National Wildlife Refuge, Beaufort Sea, Alaska, Early autumn, Octobe...

Steven Kazlowski / Polar bear (Ursus maritimus) collared sow with spring cub resting in jumbled pack ice along the Arctic coast, 1002 area of the Arctic National Wildlife Refuge, Alaska, Early atumn, October 2008

Steven Kazlowski / Polar bear (Ursus maritimus) young plump sow play fighting with a spring cub on newly formed pack ice, Arctic National Wildlife Refuge, Arctic coast, Beaufort Sea, Alaska, October 2008

Steven Kazlowski / Polar bear (Ursus maritimus) collared sow with spring cub resting in jumbled pack ice along the Arctic coast in early fall, 1002 area of the Arctic National Wildlife Refuge, Alaska, Autumn, October 20...

Steven Kazlowski / Polar bear (Ursus maritimus) collared adult sow scavenges a Bowhead whale (Balaena mysticetus) carcass as her spring cub plays with another young bear, along the 1002 area of the Arctic National Wildl...

Steven Kazlowski / Polar bear (Ursus maritimus) collared sow with spring cub resting in jumbled pack ice along the Arctic coast, 1002 area of the Arctic National Wildlife Refuge, Alaska, Early autumn, October 2008

Steven Kazlowski / Polar bear (Ursus maritimus) young plump sow playing with a spring cub on newly formed pack ice, Arctic National Wildlife Refuge, Arctic coast, Beaufort Sea, Alaska, October 2008

Steven Kazlowski / Polar bear (Ursus maritimus) collared sow with spring cub rest in jumbled pack ice along the Arctic coast, 1002 area of the Arctic National Wildlife Refuge, Alaska, Early autumn, October 2008

Donald M. Jones / Grizzly Bear (Ursus arctos horribilis) sow, Yellowstone National Park, Wyoming

Donald M. Jones / Grizzly Bear (Ursus arctos horribilis) sow nuzzling cub, Yellowstone National Park, Wyoming

Andy Rouse / Grizzly bear (Ursus arctos horribilis) sow crossing river, Alaska (non-ex)

Andy Rouse / Grizzly bear (Ursus arctos horribilis) sow showing weight gain before hibernation, Katmai Coast, Alaska (non-ex)

Andy Rouse / Grizzly bear (Ursus arctos horribilis) sow feeding in meadow, Katmai Coast, Alaska (non-ex)

Andy Rouse / Grizzly bear (Ursus arctos horribilis) sow showing weight gain before hibernation, Katmai Coast, Alaska (non-ex)

Jane Burton / Brownhead sow guinea pig with two four-week babies, UK

Jane Burton / Brownhead sow guinea pig with three newborn babies, UK

Jane Burton / Brownhead sow guinea pig with three newborn babies, UK

Jane Burton / Brownhead sow guinea pig with two four-week babies, UK

Jane Burton / Brownhead sow guinea pig with two four-week babies, UK

Jeff Vanuga / Grizzly bear (Ursus arctos horribilis) sow with cub, Spring, Mount Washburn, Yellowstone National Park, USA

Steven Kazlowski / Polar bear (Ursus maritimus) sow with cubs feeding on a bowhead whale (Balaena mysticetus) carcass on the pack ice. Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow and cub walking on multi-layer ice (freshwater pans formed over the years where the salt is squeezed out of the ice) on the Chukchi Sea, off the National Petroleum Res...

Steven Kazlowski / Polar bear (Ursus maritimus) sow and two cubs walking on ice and snow in the Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow emerging from the water, coastal plain of the Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with cubs swimming between ice on the coastal plain of the Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow and cub walking on multi-layer ice (freshwater pans formed over the years where the salt is squeezed out of the ice) on the Chukchi Sea, off the National Petroleum Res...

Steven Kazlowski / polar bear, Ursus maritimus, sow with cubs on the pack ice, 1002 coastal plain of the Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with cubs feeding on a bowhead whale (Balaena mysticetus) carcass on the pack ice. Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow and cub walking on multi-layer ice (freshwater pans formed over the years where the salt is squeezed out of the ice) on the Chukchi Sea, off the National Petroleum Res...

Steven Kazlowski / Polar bear (Ursus maritimus) sow with cubs feeding on a bowhead whale (Balaena mysticetus) carcass on the pack ice. Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow newly emerged from her den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow playing with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) den from the inside, recently vacated by sow and newborn spring cubs who have traveled to the coast in search of food. Eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs play-fighting in the snow, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with subadult cub along the edge of an open lead on the frozen eastern Chukchi Sea, Arctic Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow playing with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow playing with her cubs, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

John Downer / Cameraman Martin Dohrn filming sow birth watched by local woman, Papua New Guinea, for tv series "Lifesense"

Bruno D'Amicis / Wild European brown bear (Ursus arctos subspecies) sow with cub in sorrel field. Tatra NP, Slovakia

Rolf Nussbaumer / Lesser Goldfinch {Carduelis psaltria} female feeding on seeds of Spiny Sow-Thistle (Sonchus asper) Hill Country, Texas, USA, April 2006

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and 6 month old cub in river, British Columbia, Canada

Suzi Eszterhas / Polar Bear (Ursus maritimus) sow with twin cubs 11 months old, vulnerable, Churchill, Manitoba, Canada

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and 6 month old cub sitting on a log, British Columbia, Canada

John Downer / Huli tribal people with sow and piglets acting as plough in field, Papua New Guinea

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and six month old cub, Knight Inlet, British Columbia, Canada

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and six month old cub, Knight Inlet, British Columbia, Canada

Suzi Eszterhas / Polar Bear (Ursus maritimus) sow and 11 month old cub, Cape Churchill, Manitoba, Canada

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and six month old cub, Knight Inlet, British Columbia, Canada

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and 4-6 month old cub resting on beach, Katmai National Park, Alaska

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) female sitting upright, Katmai National Park, Alaska

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and playful young cubs on shore, Katmai National Park, Alaska

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow and 4-6 months-old cub, Katmai National Park, Alaska

Suzi Eszterhas / Grizzly Bear (Ursus arctos horribilis) sow nursing yearling cub, Katmai National Park, Alaska