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  An adult male polar bear (Ursus maritimus) lies on sea ice while "still-hunting" -- waiting for an opportunity to grab a seal as it surfaces to breathe.

  Hudson Bay, Manitoba, Canada.

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  An adult male polar bear (Ursus maritimus) traveling on sea ice.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

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  While traveling on melting summer sea ice, an adult male polar bear (Ursus maritimus) carefully presses on very thin ice to see if it will hold his weight.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

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  A subadult male polar bear (Ursus maritimus) vigorously rubs himself against the snowy sea ice to clean his fur.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

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  A subadult male polar bear (Ursus maritimus) dives from the edge of the sea ice into an open lead between floes.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

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  A subadult male polar bear (Ursus maritimus) dives from the edge of the sea ice into an open lead between floes.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

• A subadult male polar bear (Ursus maritimus) pauses while traveling on the sea ice to scrutinize a scent he has detected in the air.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• Two large, mature adult male polar bears (Ursus maritimus) confront one another warily on melting summer sea ice.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• An adult male polar bear (Ursus maritimus) pauses while traveling on melting summer sea ice. The bear has blood on his face from feeding on a seal kill.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• An adult male polar bear (Ursus maritimus) inches himself slowly backward from the sea ice into the water, to begin stalking a basking seal.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• A large, mature adult male polar bear (Ursus maritimus) on sea ice.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• An adult female polar bear (Ursus maritimus) resting on sea ice.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

• An adult male polar bear (Ursus maritimus) investigates a scent he has detected on the sea ice.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• A polar bear (Ursus maritimus) "tastes" the air to augment its sense of smell as it rests on the sea ice.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

• An adult female polar bear and her triplets (about 2 years old) travel and hunt on the sea ice.

  It is very uncommon for all three triplets to survive to this age. Triplet litters are becoming increasingly rare due to the effects of climate change on adult female polar bears. Hudson Bay, Manitoba, Canada

• An adult male polar bear (Ursus maritimus) follows a scent on the sea ice.

  Hudson Bay, Manitoba, Canada

• In an area of the Arctic Ocean with very little sea ice, an adult male polar bear (Ursus maritimus) uses scattered floes for camouflage as he attempts to hunt a seal that is resting on the ice in the distance.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• While stalking a basking seal on the sea ice, an adult male polar bear (Ursus maritimus) keeps a low profile after climbing out of the water.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• While stalking a basking seal on the sea ice, an adult male polar bear (Ursus maritimus) keeps a low profile as he attempts to approach his quarry.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• An adult male polar bear (Ursus maritimus) carefully slips into the water without making a splash to begin an aquatic stalk of a basking seal.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• An adult male polar bear (Ursus maritimus) carefully slips into the water without making a splash to begin an aquatic stalk of a basking seal.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• A large, mature adult male polar bear (Ursus maritimus) on melting summer sea ice, feeding on a seal kill. Glaucous gulls (Larus hyperboreus) and an ivory gull (Pagophila eburnea) are also eating bits of the carcass.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• An adult male polar bear (Ursus maritimus) resting on sea ice after gorging on a seal kill. He is positioned to keep an eye on the remaining carcass. Glaucous gulls (Larus hyperboreus) are squabbling over scraps of meat.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• A subadult male polar bear (Ursus maritimus) vigorously rubs himself against the snowy sea ice to clean his fur.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• An adult female polar bear and her triplet cubs follow a scent as they travel and hunt on the sea ice near the front of a tidewater glacier.

  Northern Novaya Zemlya, within Russkaya Arktika National Park, Russia.

• A subadult male polar bear (Ursus maritimus) swims among floes of melting summer sea ice as he travels and hunts for seals.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

• An adult female polar bear (Ursus maritimus) swims among melting floes of summer sea ice as she travels and hunts for seals.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

• An adult female polar bear (Ursus maritimus) uses floes of sea ice for camouflage as she hunts a seal that is resting in the distance.

  Olgastretet, Barents Sea (Arctic Ocean), within the Svalbard Archipelago, Norway.

• Two large, mature adult male polar bears (Ursus maritimus) on melting summer sea ice, feeding on a seal kill. Glaucous gulls (Larus hyperboreus) and an ivory gull (Pagophila eburnea) are also eating bits of the carcass.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.

• A young adult female polar bear (Ursus maritimus) "still-hunting " in brash ice near the face of a glacier -- waiting for an opportunity to grab an unsuspecting seal as it surfaces to breathe.

  Northern Novaya Zemlya, Barents Sea, within Russkaya Arktika National Park, Russia.

• An young adult female polar bear (Ursus maritimus) "still-hunting " in brash ice near the face of a glacier -- waiting for an opportunity to grab an unsuspecting seal as it surfaces to breathe.

  Northern Novaya Zemlya, Barents Sea, within Russkaya Arktika National Park, Russia.

• An adult male polar bear (Ursus maritimus) swims in calm seas as he travels in an area of the Arctic Ocean with no sea ice.

  Arctic Ocean north of the Svalbard Archipelago, near 81-degrees North.