Majestic giants of the Arctic

Polar bears are uniquely adapted to survive in one of the harshest environments on Earth. We picture them as the apex (top) predators on land (which they are), but they are actually marine mammals, capable of swimming long distances between ice floes or between distant points of land. In fact, a bear might travel 1500-15,000 square miles in a year in search of prey, using a combination of swimming, walking, and floating on ice floes. They can swim continuously using their powerful forelegs for 3-4 days at a time, covering more than 100 miles.

This bear was spotted while swimming and occasionally diving so we slowly followed it in the ship (from a long distance) until it finally dragged a piece of a reindeer carcass onto the rocky shore. It chewed on the carcass for a while and then moved away to have a roll in the snow. You can see that the bear is wearing a geolocation collar, so we know it’s a female. Male bears have such thick necks that the collar slips off their smaller diameter heads.

From its rotund appearance this seems to be a well-nourished bear that has been successful finding seals, or belugas, or even young walrus to feed on recently. As the sea ice disappears in the summer so does their favorite food source — bearded or ringed seals. In the summer polar bears resort to attacking reindeer (caribou) or arctic fox, or feed on marine invertebrates or berries or even kelp along the coast. Thus, summer is the more stressful time of the year for polar bears, because their sea ice hunting grounds are gone and air temperatures are higher, making them overheat while walking on land.

Cold tolerance is one of the key adaptations of all arctic mammals, but polar bears have evolved their own unique method of achieving it. Their fur coat consists of two layers, a short dense underfur, and a longer fur of guard hairs that are hollow spaces, lacking pigment, surrounded by a thick keratin shell. This one characteristic turns out to be the key to heat conservation for polar bears because heat from the skin that radiates toward the surface, first through the dense underfur, and then through the guard hair layer is trapped in the slender, air-filled tubes. This system works so well to trap the bear’s heat that they are invisible to thermal imaging! In addition, like other marine mammals, polar bears carry a thick layer of blubber beneath the skin as additional insulation. Of course all this insulation then makes the polar bear vulnerable to overheating in the summer sun.

Sometimes they just need to cool off in the chilly (near freezing temperature) water. We spotted these two polar bears on a rocky island, and we set out in groups in the small zodiacs to observe them more closely. Eventually they both left the island and played around in the water for a few minutes, giving us good views of their swimming ability. It’s uncertain whether this was a courting pair or a mother and her very large offspring, but they seemed very amicable toward one another. Polar bears are not social animals and are usually solitary except for mother and cubs.

Eagle eyes spotted the two bears on the island (above the blue markers) and photographers began clicking away with long telephotos as we bobbed up and down in the zodiacs. This was challenging! Click on the image to zoom in and find the bears above the blue markers. (Photo by Debbie Reynolds)

Close-up shots of these two bears gave us a chance to admire their other characteristics. Polar bears are huge. A big male might be 5 feet at the shoulder and its head might be at 10 feet when the bear stands up on two legs, which is a useful behavior when trying to spot seals lying on the ice. And their feet are huge, flat, dinner-plate sized pads with hair on the bottom of the pad to provide some friction against icy surfaces. Short but very sharp claws at the tips of the digits of the front paws are essential for gripping the ice shelf to propel them from the water onto the ice and for latching onto their prey.

(Photo by Debbie Reynolds)

Polar bears have long snouts, small ears, and very small eyes. They use their heightened sense of smell to detect the presence of potential prey, rather than their eyesight. In fact, they can smell seals and other marine mammals on the ice from 20 miles away, and even detect a seal’s breathing hole from a half mile away. Their jaws are not large or particularly powerful, but their teeth are adapted for a carnivorous diet with very sharp canines and a space between canines and molars to accommodate biting off large chunks of meat.

(Photo by Debbie Reynolds)

Polar bears adapt their hunting strategies to their prey with a combination of stalking, camouflage, sit-and wait (by a breathing hole), and surprise attack from behind their prey. The video by David Attenborough below shows their behavior well. It’s significant to note, however, that these sorts of surprise attacks are only successful about 5% of the time!

(If you’re reading this post in your email, you won’t be able to see the video. Instead click on the title of the blog post to take you directly to the blog URL to view the video,)

Majestic apex predators of the arctic — what a treat to see them in action!