Most everyone knows that polar bears are adapted to cold.
Polar bear adaptations to cold extend to water as well. Polar bears are excellent swimmers and can swim for long distances in water very near the freezing level. In fact they have been observed swimming in open water, miles from any shore. Their ease in getting around in the water and on the sea ice has led to them being classified as a marine mammal, just as seals, dolphins and whales are, for legal protection purposes. They are protected in the United States under the Marine Mammal Protection Act.
One biologist even described polar bears as a transitional animal in the process of evolving from a land animal to a marine animal. Of course, one can’t know where the evolution of a species will end up, but it is an apt description of a species that has made major adaptations to a marine habitat.
Among other polar bear adaptations to the far north is the yellow-white coat, coupled with a black skin and hollow fur. The bears’ coat color certainly acts to camouflage it when on the ice. Anyone who has spent any time in the Arctic with polar bears will tell you tales of looking right at a pale object and not being able to tell if it’s a bear until it moves. The hollow fur actually acts to transmit the dim Arctic sunlight (sort of like a fiber optic thread conducts light) to the dark skin where it is absorbed as heat. Several inches of subcutaneous fat in a healthy bear also act as insulation against the frigid winter and cold sea water as well as storage of energy for their long periods of fasting during the summer months.
Polar bear adaptations to the harsh Arctic environment extends to the very way they bear their young. Females typically mate on the ice during the early spring. If her eggs are successfully fertilized, she delays implantation of the zygote in her uterus until she can successfully den when the snow accumulates in the fall. She then carries her pregnancy to term through the winter, safe in her den.
In spring, typically March, the Arctic is still snow-bound and frozen, but the female emerges from her den with her young, ranging from one to three cubs (two is typical). These little cubs of the year (COY) are small and defenseless, but since all of the other non-breeding bears are far out on the sea ice hunting for seal, the mother does not have to worry about her cubs being harmed. She will then take the cubs out onto the sea ice for what is typically her first meal in up to seven or eight months! This is a critical period for both her and her cubs: if she is not able to catch enough seal to eat, her cubs and even herself might not survive.
For one of the best works on polar bear adaptations and evolution, read Canadian polar bear researcher Dr. Ian Stirling’s book Polar Bears. You can find the book on Amazon – clicking on the link below will open in a new window.