Scientists fear the future looks grim for polar bears. Photo / AP
It seems like every time we turn around, polar bears are catching a
tough break. As climate change continues to heat up the planet and
Arctic sea ice retreats further each year, conservationists are
increasingly concerned that the bears – which use the sea ice as a
hunting ground for catching seals – will have less access to the food
they need to survive.
It’s been an ongoing worry for years, and
last week the United States Fish and Wildlife Service drove it home
again with a new conservation management plan, which identifies climate
change and sea ice loss as the primary threat to polar bears.
all the doom and gloom, some research conducted in the early 1980s has
helped conservationists maintain a glimmer of hope about the polar
bear’s ability to survive long periods of time without food. This
research found evidence in polar bear blood samples to suggest that the
bears might go into a kind of “walking hibernation” when food is scarce,
staying awake but significantly lowering their metabolism to use less
energy. This would be a useful adaptation during the summer, when sea
ice is at its lowest extent and hunting is most difficult.
been a tempting theory for more than 30 years – but once again, we’re
looking at bad news for the polar bear. A new study, published yesterday
in Science, debunks the “walking hibernation” idea with data collected
from more than two dozen captured polar bears in the Arctic’s Beaufort
Sea, which the researchers spotted and tranquillised from helicopters.
researchers, led by biologist John Whiteman at the University of
Wyoming, outfitted bears with devices that collect and transit data
remotely to collect data on the bears’ movement and activity and their
body temperature. Their sample included both “ice bears” and “shore
bears” – that is, both bears who choose to chase the ice as it retreats
north in the summer, looking for seals, and bears who choose to spend
their summer on shore.
The researchers expected that if bears did
indeed exhibit walking hibernation, their activity and temperature
would drop down to the kinds of levels usually observed in other bears
during true hibernation – that is, very low levels.
“If there was
hibernation metabolism … you would see all of them have a very steep,
abrupt decline in body temperature to about 35C and then remain like
that the whole period,” says senior author Merav Ben-David, a professor
of wildlife ecology at the University of Wyoming. “But we don’t see
Instead, the results showed that both ice bears and shore
bears experience much more moderate declines in body temperatures during
the summer, when food is scarce – just the kinds of declines you would
expect to see in any mammal that wasn’t getting enough food.
you went into an extended fast, your body temperature would decline,
too,” Ben-David says. “It’s a normal mammalian response to fasting and
losing metabolically active tissue – losing weight.”
this means polar bears have no special protections against starvation
as previously thought. They simply exhibit a typical fasting response to
food deprivation, and – given a long enough time without food – will
There are an estimated 20,000-25,000 polar bears, grouped
into 19 sub-populations. While scientists don’t have adequate data for
all the populations, we know at least some of them are declining, and
the polar bear is currently protected under the Endangered Species Act.
Scientists worry that their populations will suffer worse declines in the future as sea ice continues to melt.
more information about the bears’ activity can help scientists develop
more accurate models about how they will withstand food deprivation and
what will happen to their populations, says Whiteman, the lead author.
When producing these models, scientists now know to plug in a normal
metabolic rate for the bears rather than assuming they may go into
It’s worth noting that while polar bears
didn’t show any signs of walking hibernation, the study did produce
evidence for another kind of special adaptation that may help bears
survive under stressful conditions.
The data suggests that when
bears swim in the Arctic water for extended periods of time – longer
than a few minutes, according to Ben-David – they can cool down the
outer parts of their body cores so less body heat is lost to the frigid
“This is an exciting new finding and something we didn’t
know about the bears,” Whiteman says. And it may be increasingly useful
in the future when retreating sea ice forces bears to swim for longer
periods of time to get between the ice and the shore.
not to say they can swim forever. One of the bears being tracked swam
for nine days and amazingly survived the journey, but lost nearly a
quarter of her body mass by the time she came out of the water.
it’s all said and done, the results of the study confirm that polar
bears aren’t superheroes – they’re susceptible to the same kinds of
stresses, including food stress, that other animals are.
while the paper gives us some deeper insights into the bears’
physiological responses to tough times, Whiteman cautions that there’s
still a lot left to learn.
“We’re not looking at any quantitative
predictions for what will happen to the bears in the future in terms of
climate change,” he says. “There still are some fundamental aspects of
polar bear biology that we have yet to understand.”