Overview
Polar bears are the largest land carnivore on earth, found around the circumpolar Arctic where the average air temperature can reach freezing in the summer. The first polar bears came about around 100,000 years ago, decedents of an ancestral brown bear. They are known to prefer habitats that include sea ice, water, islands, and continental coastlines.
Male polar bears, known as boars, can weigh up to 1,435 pounds and grow as long as10 feet, the same as an NBA-regulation size basketball hoop. Their female counterparts, called sows, weigh between 330 pounds and 550 pounds and as much as 1,100 pounds when pregnant. Mature sows reach between 6 and 8 feet in length.
A polar bear’s coat is white and sometimes a creamy yellow color depending on the light. With the exception of their black noses and five-toed paws, polar bears are completely covered in a fur coat that’s 2.5 to 5 centimeters thick. When submerged, a polar bear’s nostrils close, and its small and rounded ears lay flat to keep icy waters out.
Polar bears, like all mammals, maintain a body temperature of 98.6 degrees Fahrenheit aided by their thick coat of fur, a tough hide, and a layer of insulating blubber, or fat. In fact, polar bears are so well insulated from the cold they sometimes will overheat. To prevent this, polar bears often move slowly and rest frequently. They’re also known to go for dips on hot days or after excessive physical activity.
Diet
Polar bears are exceptionally strong swimmers, traversing bays and leads, cracks in the ice, with ease. Their front paws create a dog-paddle motion to propel them through the water while their hind feet and legs work as rudders. Polar bears do dive when stalking prey and navigating ice floes, though it’s estimated that polar bears usually swim at depths of around 9 to 14 feet. They can remain submerged for as long as two minutes.
Hunting is the polar bear’s primary means of securing food, and polar bears use four methods to capture prey: still hunting, land stalking, aquatic stalking, and stalking birthing lairs.
- • Still hunting is a year-round method of hunting in which the polar bear lays near a hole or ledge and waits for a seal to surface. Once its meal appears, the polar bear bites its head. This method takes around an hour, but polar bears can wait motionless for much longer.
• Land stalking is practiced during summer months when seals haul out on sea ice. A polar bear will observe its prey from a distance of roughly 50 feet before suddenly charging in, using its claws and paws to grab the seal before it can escape.
• The aquatic stalk is also used to snatch seals from the sea ice during summer months. The polar bear will swim over to the hauled-out seal, quickly emerging from the water and stealing its prey away.
• Most commonly a female polar bear with a cub less than 1 year old will stalk birthing lairs in the springtime after ringed seals have given birth to their pups. Lairs are caves built into the snow next to a hole in the ice, and once a polar bear spots a lair it will hang around using its acute hearing and smell to snuff out a seal. After pinpointing it prey, the polar bear will rise to its haunches and crash into the roof of the birthing lair sometimes repeatedly to collapse the hard surface.
Polar bears must consume an average of 4.5 pounds of fat daily to survive and can eat as much as 15 percent of their body weight. For a boar, that could be upward of 200 pounds every day! To satisfy this massive appetite, polar bears feast mainly on ringed and bearded seals but have also been known to eat harp and hooded seals. Nabbing just one mature ringed seal could provide a polar bear with eight days of energy, but if no seals are available, a polar bear may also consume other marine mammals, sea birds, reindeer, vegetation, and even human garbage. Occasionally, a polar bear will hunt a young walrus or beluga whale or scavenge the carcasses of other whales.
Reproduction
Scientists have observed boars following the tracks of breeding sows up to 62 miles during the mating season, which spans the months of April and May. Male polar bears reach sexual maturity at age 6, while females mature at age 4. It’s uncommon, however, for polar bears to successfully mate until the age of 8 to 10.
Males and females find each other during the mating season by congregating around the best seal-hunting grounds on the sea ice. Competition for females is pretty intense since sows breed once every three years, resulting in a 3:1 male-to-female ratio. Males fight fiercely among themselves until generally the strongest and largest animal chases the others away. Fights are rarely fatal, and the victor pairs for a week or more with the female, though it may take several days of mating to guarantee fertilization of the egg. Polar bears are known to have many mates over a lifetime, and the most dominant males will likely have multiple mates over a season.
Threats
Polar bears are protected under the Marine Mammal Protection Act of 1972. The most notable threat facing polar bears today is the literal melting of their habitat due to global warming. Studies have reported polar bear hunting grounds are receding at a rapid rate, increasing polar cub mortality rates and forcing mature animals to the shores before they’ve caught enough food to last them through hibernation.