Scientists from a Danish university compared nearly 300 polar bear skulls collected by a zoological museum in Copenhagen. They found that the skulls collected during the latter half of the 20th century were between two and nine per cent smaller than those collected during the previous 50 years and had also changed shape.

Professor Cino Pertoldi of Aarhus University, who led the study, believes that the bears are shrinking because the ice is melting and they are consequently having to use more energy to hunt down food. ‘Climate change has contributed to the “shrink” but is probably not the only cause,’ he said.

He isn’t so sure why the bears’ skulls have changed in shape, but believes that it could be caused by inbreeding as a result of the bears’ shrinking gene pool, or due to pollutants.

‘[Polar bears] are on the top of the food chain, so they are biomagnifying the contaminants contained in their prey from lower levels of the food chain,’ said Pertoldi. The contaminants are liposoluble, so they are stored in the bear’s fat until their energy reserves fall too low. ‘Then the contaminants start to circulate in the body of the bear producing deleterious effects.’

November 2009