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Polar bears are shrinking in size -

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Polar bears are shrinking in size

Carly Laird reported this story on Wednesday, August 26, 2009 12:50:00

ELEANOR HALL: Scientists in Denmark are warning that polar bears are getting smaller.

The researchers say the reduction is linked to climate change but that the change in the animals'
skulls also suggests there are genetic problems and that this could affect the bears' ability to

Carly Laird compiled this report.

DAVID ATTENBOROUGH: Polar bears are the most modern bear, having evolved from the grizzly just
200,000 years ago.

CARLY LAIRD: But over the past century, things have taken a turn for the worse for polar bears.

DAVID ATTENBOROUGH: The largest carnivore in the world has to be careful. She's walking on thin

(Sound of ice breaking)

CARLY LAIRD: A study from Denmark compared the sizes of the mammals' skulls over the last 120

The scientists took older skulls from the Zoological Museum of Copenhagen and compared them with
those used in more recent scientific research.

Cino Pertoldi, a Professor of Biological Science at Aarhus University in Denmark, is the study's
lead author.

CINO PERTOLDI: We investigated the skulls, the change in the skulls, we can determine the change in
the body size. So we have seen a reduction in the skull sizes which we presume is due to the fact
that there's a worsening of the environment.

CARLY LAIRD: It wasn't so much the increasing temperatures that caused problems for the bears, but
the reduction in sea ice.

CINO PERTOLDI: Bigger mammals like polar bears can of course compensate for change in the
temperature but climate change means you have a reduced the area where the polar bear can hunt and
sometimes they have to swim from one part to the other in order to find some prey to eat.

CARLY LAIRD: The theory is that the polar bears are spending so much energy moving around that they
have less left over for growing.

Cino Pertoldi says the reduction they found in the skull size was profound.

CINO PERTOLDI: We observed a reduction between 2 and 9 per cent of the skull size, which is quite
big considering the generation time because the generation time of a polar bear is quite long so
we're speaking about a strong reduction in size in few generations.

CARLY LAIRD: An increase in chemical pollution, the scientists say, is also causing a reduction in
the polar bears' fertility rates.

CINO PERTOLDI: We suspect that the contaminants in the polar bear have affected the reproductive
capacity of many of these individuals.

CARLY LAIRD: The researchers say reduced fertility is leading to more inbreeding and this in turn
has changed the shape of the bears' skulls.

Cino Pertoldi says the polar bears are particularly affected by polluting chemicals because they're
at the top of the food chain.

CINO PERTOLDI: They're one of the most contaminated individuals in the world, I mean, because they
are accumulating all the contaminants from all animals below the food chain, so from fish, seals -
and all these contaminants are of course accumulating in the fat and the polar bear quite fat.

CARLY LAIRD: And for those who've never seen a polar bear, despite their reduction in size, Cino
Pertoldi says they're still a big animal.

CINO PERTOLDI: Ah no they're really big (laughs). Like the size of a horse skull but much wider and
with big, very big teeth but this bear is still surviving.

CARLY LAIRD: The study was published in the Journal of Zoology.

ELEANOR HALL: Carly Laird reporting.