Polar Bears only have a limited time for hunting on sea ice and they are now shifting their migration patterns due to the global warming climate change.
A team of researchers studied the migration patterns of 109 female polar bears in Hudson Bay, Canada, using satellite-tracking data collected between 1991 and 1997 and 2004 and 2009. Male bears can not be tracked with the radio collars as their necks are wider than their heads and the devices would fall off.
The team, led by Dr Seth Cherry, of the University of Alberta, Canada, also monitored the position and concentration of sea ice using satellite images.
“At first glance, sea ice may look like a barren, uniform environment, but in reality, it’s remarkably complex and polar bears manage to cope, and even thrive, in a habitat that moves beneath their feet and even disappears for part of the year. This is an extraordinary biological feat and biologist still don’t fully understand it,” Dr Cherry says.
They found that the rate at which sea ice melts and re-freezes, as well as how the ice is distributed around the bay, predicted when the bears migrated onto or off of land. The findings were published in the Journal of Animal Ecology on March 19, 2013.
Tracking the polar bears revealed them arriving onshore earlier in the spring and departing later in the autumn.
“Keeping track of when polar bears move on and off the ice is an important aspect of monitoring the risks to the population associated with climate change,” study leader Seth Cherry, a graduate student in ecology at the University of Alberta, Canada, told LiveScience in an email.
The study reported that early melting of the sea ice will have negative impacts on polar bear energy budgets because it shortens the hyperphagic period of late spring and early summer, when hunting conditions are most favorable, and extends the duration of the on-land period through which polar bears must survive on reduced and finite stores of body fat.
Cherry said, “The data suggest that in recent years, polar bears are arriving on shore earlier in the summer and leaving later in the autumn. These are precisely the kind of changes one would expect to see as a result of a warming climate and may help explain some other studies that are showing declines in body condition and cub production.”
He hopes the results will enable other scientists and wildlife managers to predict how potential climate-induced changes to sea ice freeze-thaw cycles will affect the ecology, particularly the migration patterns of polar bears.
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