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fall. “While on land during the summer,” says the National Wildlife
Federation, “these bears eat little or nothing.”
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When the bitterly
cold winter returns and the bay is once again frozen, the bears
can venture back onto the ice and hunt for seals.
Research has shown that over the past two decades, the
ice-free period in Hudson Bay has increased by an average of
twenty days. What that means for polar bears is that their time
to hunt for food has declined by nearly three weeks. As a result,
says the National Wildlife Federation, the average weight of polar
bears has dropped by 15 percent, which in
turn has caused reproduction rates to de-
cline. Another problem caused by melting
Arctic ice is that the remaining ice keeps
moving farther and farther from shore,
and the distance between sheets of float-
ing ice (known as ice floes) continues to
widen. Polar bears typically swim about 30
miles (48.3km) at a time. Because of rap-
id ice melt, however, there are now larger
stretches of open water that the creatures
must swim across in order to reach ice. This creates a hazardous
situation for them and has led to a number of drownings.
In 2011 scientists at the US Geological Survey (USGS) used
a tracking device to record the journey of a female polar bear in
the Beaufort Sea, which is north of Alaska. Accompanied by her
yearling cub, the female swam more than 400 miles (643.7km).
For nine days the bear swam continuously, trying to reach an ice
floe where she could hunt for food. “We are in awe that an animal
that spends most of its time on the surface of sea ice could swim
constantly for so long in water so cold,” says USGS zoologist
George M. Durner. “It is truly an amazing feat.” Yet the unbeliev-
ably long swim came at a very high cost for the bear. She lost an
estimated 22 percent of her body fat, and along the way her cub
drowned. “It was simply more energetically costly for the yearling
than the adult to make this long distance swim,”
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says Durner.
He adds that as the planet continues to warm, the stretches of
open water will keep widening.
WORDS IN
CONTEXT
ice oes
Sheets of floating
ice in the Arctic and
Antarctic Oceans.
