Polar bears mouthing off at the weigh-in

Male polar bears on the edge of Hudson Bay in Canada "mouth" each other before beginning to spar. Such fights are just for play but during the mating season, as the bears wrestle for supremacy, the fighting can be brutal.

Polar bears are the world's largest land carnivores, adult males weighing more than half a tonne. The animals are listed as a vulnerable species as their habitat is shrinking owing to global warming. Some scientists have predicted they will be extinct before the end of the century.