Polar bears' territorial tendencies and the diminishing ice season on Hudson Bay are conspiring to leave the animals less time to eat, researchers say. This bodes ill for their ability to reproduce, and survive.
A polar bear walks along the shore of Hudson Bay near Churchill, Manitoba, in 2010.
Chris Wattie/Reuters
EnlargeFor polar bears that pad and paddle around Hudson Bay, the trend toward an earlier melt and later freeze of Arctic sea ice is altering the timing of their seasonal migration in ways that leave the animals less time to feed.
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Ice floes on the open water serve as hunting platforms for the bears, whose wintry diet of seals, snagged as they come up for air through breaks in the ice, builds the fat reserves polar bears need to survive on land during the sea-ice melt season.
The migration changes likely bode ill for the ability of the population to reproduce and to survive over the long term as global warming continues to build, say researchers who conducted a study published this week on the impact of climate on the area's polar bear migration patterns. The study appeared in Tuesday?s issue of the Journal of Animal Ecology.
Moreover, because the bears appear to have a strong sense of home turf, the researchers say the animals are likely getting off the melting ice earlier in order to return to familiar turf. If they stay on the moving ice to feed longer, they risk disembarking where they will have to spend more time and energy either returning to their usual range or exploring the new location for the best places to hunker down for the melt season.
The research team, led by University of Alberta biologist Seth Cherry, points out that this pickiness about territory would ordinarily work to the benefit of females bearing cubs. The mothers-to-be would not have to spend extra energy wandering in search of dens, because they already know where the best dens are located.
Polar bears, which the US Environmental Protection Agency listed as an endangered species in May 2008, have become fuzzy poster children for the some of the ecological effects of global warming ? with reason, notes Dr. Cherry.
"It's true the public and media alike may be disproportionately concerned about polar bears" versus other ecological players above the Arctic Circle, he says. "However, there is scientific merit to the hype over polar bears and climate change."
As apex predators in the Arctic, he explains, polar bears sit at the top of the marine food chain. Monitoring their range, movement, and physiology makes them useful barometers for gauging larger environmental changes ? in this case, global warming. And because they rely so heavily on the integrity of the food chain that supports them, they represent an early-warning?network for changes that may be taking place with links father down the chain.
A US Geological Survey analysis of polar-bear population studies, published in 2010, put the number of polar bears Arctic-wide at some 24,600 animals. Some 5,000 roam the islands making up the Canadian Archipelago. About 11,900 animals are spread along the continental coasts open to the Arctic Ocean. Some 7,700 live around bays and basins where all the sea-ice tends to be seasonal, instead of a mixture of seasonal and multi-year ice. Hudson Bay falls into this category.
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