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Why do we have the polar bears in our masthead? Of course they are fuzzy and cute, but they are also one of the most illustrative symbols of the effects of climate change on wildlife as they require an environment that is being rapidly changed by a warmer climate.
Exceptionally intelligent and curious, polar bears are the largest terrestrial carnivores, with adult males typically weighing up to 1,500 pounds (680 kg) and measuring up to 10 feet (3 m) in length. Females are typically about half the size of males. Their senses are highly developed, especially their sense of smell, patience, and swimming ability is legendary. But they are powerless when faced with a warming environment and rapidly melting sea ice.
Polar bears are residents of the Arctic, venturing as far south as James Bay, in northern Ontario, Canada. Polar bears typically inhabit the edge of the Arctic ice pack, rather than the interior toward the North Pole, especially the boundary area between the ice pack and the water where they hunt for the bearded and ringed seals which are their primary source of nutrition. While polar bears may occasionally eat vegetation, berries, bird eggs and other scavenged food, their diet is largely restricted to seals, whose (fat) is essential for their survival. It is this dependence upon hunting for seals, that ties the polar bears to the edge of the Arctic ice pack.
Polar bears mate on the sea ice during the spring (April, May). The pregnant females then gorge themselves on food, often doubling their body weight. When the sea ice breaks up in late summer or fall, the females construct a den, typically on shore, but in some cases on the interior of the ice pack, where will stay in a state of semi-hibernation until spring. The cubs (usually 2) are born in mid-winter and remain in the den with the female until spring. After leaving the denning area, the mother and cubs return to the sea ice where the female can again for hunt seals and feed. Depending upon when the ice pack break up occurred the previous fall, she may have fasted for up to eight months, while nursing her cubs(1).
The survival of polar bears depends upon summer sea period of sufficient duration, and an adequate population of seals, so that the pregnant females can nourish their offspring during the long winter months. As a species, the adult bear metabolism is geared to seal blubber as their primary energy source. Climate change is reducing volume, extent and duration of Arctic sea ice, with a completely ice-free season predicted to occur in a relatively few years. The reduced extent of sea ice forces the bears to swim greater distances, resulting in an increase of drownings(2), while thinner ice reduces hunting efficiency, and a shorter duration of ice cover reduces the opportunity to build the body fat reserves necessary to survive the ice-free period, and for pregnant females the winter denning/nursing periods(3). A shorter period of sea ice cover will also increase polar bear/human interactions as bears are driven closer to human habitation and the human population of the Arctic increases with the increased opportunities for oil and other mineral extraction.
With their dependence upon the sea ice, and seals, the only hope for survival of polar bears as a species is a sudden reversal of Arctic warming, which is highly improbable, or zoos. We must also remember, that literally thousands of other species also have specialized habitat and nutritional requirements and are also threatened with extinction due to climate change(4). Thus the polar bear is indeed an appropriate symbol of the effect of climate change upon the wildlife of our planet.
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1.) Stirling, Ian (1988). "Reproduction". Polar Bears. Ann Arbor: University of Michigan Press. ISBN 0-472-10100-5
2.) Monnett, Charles; Gleason, Jeffrey S. (July 2006). "Observations of mortality associated with extended open-water swimming by polar bears in the Alaskan Beaufort Sea". Polar Biology (Berlin: Springer) 29 (8): pp. 681–687.
3.) Stirling, Ian; Lunn, N. J.; Iacozza, J. (September 1999). "Long-term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change". Arctic 52 (3): pp. 294–306.
4.) ICUN Red List of Threatened Species. http://www.iucnredlist.org/.
