Al Gore and others have shamelessly exploited public ignorance about the polar bear in order to spread fear. Ed Caryl tells us why the polar bear will do just fine.
The Polar Bear
by Ed Caryl
The climate change “team” regularly invoke the polar bear as the “poster-boy” for the supposed danger in catastrophic anthropogenic global warming.
Figure 1: Female polar bear (ursus maritimus) near Kaktovik, Barter Island, Alaska. (Source: Wikimedia Commons).
The polar bear, ursus maritimus, is descended from the Brown Bear, ursus arctos. The genetic split took place sometime between 300,000 and 600,000 years ago, but the split was never fully complete. Polar bear mitochondral DNA (mDNA) is descended from a female brown bear, perhaps from Ireland, which dates back to the middle of the last ice age, 50,000 to 100,000 years ago. During that encounter, a male polar bear mated with a female brown bear. The subsequent offspring then mated with polar bears, and the mDNA from that female spread across the population. That suggests that population pressure on polar bears doesn’t necessarily happen only when it warms up, but also when it gets very cold. Both conditions reduce the first-year sea ice that makes prime habitat for the seals that polar bears favor; cold covers it with glaciers and warm melts it.
There isn’t much genetic difference between polar bears and other brown bears. They can freely mate, and the offspring are fertile, indicating that they are the same species. The Latin name should be ursus arctos maritimus, similar to the grizzly bear ursus arctos horribilus. These “hybrids” happen often in the Canadian Arctic, and even have locally bestowed names, Grolar or Pizzly Bears. The environmentalists have decried these occurrences, claiming that it will lead to the demise of their favorite animal. In my opinion, this provides genetic diversity that has assisted survival in the past, and will in the future.
Like all bears, polar bears are omnivorous. They eat anything organic. Except for man, they are the apex carnivore in the Arctic. They hunt and eat everything, sometimes
including man-flesh, sometimes including their own species. After a meal of seal blubber, they will sometimes seek out grass for a salad. In the summer, when they are ashore, they do not starve. They will hunt birds, forage for eggs, hunt and kill caribou and small mammals, eat lichen, moss, and mushrooms, forage on shrubbery and berries in season, harvest kelp and other seaweed, eat fish, shellfish, and other sea invertebrates, as well as sort through man’s local garbage. They have been seen hunting sea birds and ducks by swimming under them and ambushing them from below. They hunt and kill beluga whales, narwhales, and walrus twice their size. Obversely, the only animal that can kill a polar bear is man. Most carnivores kill by strangulation; polar bears kill by crushing the skull of their prey in their jaws.
The polar bear population is always food-limited. If food is plentiful, mother bears can raise more cubs and the population increases. The Arctic is not a place where food is easily obtained, so it takes 25,000 to 50,000 square kilometers to support a bear family. If food is plentiful, bear density may be limited by male bear predation on cubs
not their own. Cubs, if readily available, are an easier kill than seals. In recent years, seal and bear hunting in Arctic Canada has been curtailed, increasing both the seal and bear population. Bears are not being hunted (except for about 500 a year by natives in Nunavut, and illegal hunting in Russia) so the only mortality is old age, disease, parasitism (primarily trichinosis), and starvation. On autopsy, all four causes of death look very similar. Because of some hunting, the bear population in Nunavut seems to be the healthiest, and may be growing despite the hunting, due to the increasing number of seals.
Habits and Habitat
In the spring, polar bears prefer hunting seals on first-year sea ice. At that time of year, seals are almost the only food source available, plus they are high in fat, a prime source of energy. The bears hunt seals by staking out a breathing hole. Seals may have several holes each, so hunting is primarily a waiting game. As the sea ice melts, bears turn to seal haul-out locations and seal pups. As the season further advances, other species such as walrus, belugas, and narwhales may become available. Ursus maritimus lives up to the Latin name with ability to swim long distances. The record for a female wearing a GPS color is over 600 km in 9 days, though the mean distance and time for the bears in this study was about 100 km over three days. One female bear was tracked from Prudhoe Bay in Alaska to Greenland. (Factoid: only female bears are collared, because of the male bear anatomy. Male bears have such a muscular neck that a collar won’t stay on.)
The mating season is in the late spring, blastocyst (fertilized egg) implantation is delayed until fall. Bears den-up in October and the one to three one-pound pups are born in November or December. Mother and cubs do not emerge until March or April. Dens are in snowdrifts ashore or, north of Greenland, in multi-year ice where pressure ridges form shelters. Polar bears don’t really hibernate, but they do sleep a lot when denned. They also fast during this period. A female polar bear can fast for up to eight months and still be capable of nursing cubs and hunting. Cubs stay with their mother for two years in the low Arctic and up to three years in the high Arctic. During this period the cubs learn to hunt from their mothers.
All the above is similar to grizzly bears. Grizzly bears also hunt seals on sea ice, and polar bears will hunt caribou on land, just like grizzlies. The differences are fairly minor: grizzlies have a fat hump that polar bears lack; polar bears have clear, hollow shaft fur that appears white, black skin and thick fur on their paws which grizzlies lack. Pizzlies tend to have the clear fur, with black around the nose and eyes, with a grizzly head shape. The clear insulating fur and black skin is an adaptation to the Arctic that minimizes heat loss when it is dark and maximizes heat gain when it is sunny. For a polar bear, high energy efficiency means fewer seals are required to live and reproduce. The clear fur also provides camouflage, but this is only an advantage when stalking seals on ice.
The polar bear population is food-limited, not ice limited. Polar bears wander over wide areas. They do not have a fixed territory. The population freely intermingle. If sea ice recedes in one area, bears move to where it remains. When it all melts, they move to land. If they find themselves on an island with no food resources, they swim to the next spot of land. In the Arctic, polar bears and humans compete. If the bear and human populations use up the food resources in an area, both populations move somewhere else, or limit reproduction.
The polar bear population may be near the historic high at 20 to 25,000 animals. In the 1950’s and 60’s, the population may have been as low as 5,000. Sea-ice extent is cyclical. Bears have withstood many cycles of sea-ice shrinking and growing, including previous interglacials. The polar bear population is in no danger.
Also read an excellent article here: polar-bears-polemics-and-climate-warming/