Polar bears have smelly feet, scientists have discovered.
Not just feet that are stinky because they are dirty, or unwashed. But feet that distribute scent, allowing the bears to leave chemical trails wherever they walk.
That in turn allows the bears to scent-mark their huge, often barren territories, and communicate over vast distances.
The new insight is published in the Journal of Zoology.
Polar bears have the largest range size of any bear. They also tend to wander alone, and breed at certain times of the year. Which means it's not common for bears to meet.
Scientists have also recorded anecdotal evidence that polar bears occasionally sniff each other's tracks, even deciding to follow the tracks of one bear over another having had a smell.
So Megan Owen, of the Institute for Conservation Research at Zan Diego Zoo, California, in the US, and colleagues from Polar Bears International and the US Geological Survey, decided to investigate.
Males were especially interested in female bears in oestrus
They took samples of the scent left by the feet of 203 wild polar bears living around either the southern Beaufort Sea or the Chukchi Sea in the Arctic Ocean.
The scientists then offered these scents to ten adult male polar bears and 16 adult females, both wild- and captive-born, living in ten different zoo across North America.
The zoo bears were more attracted to scents left by wild bears in the spring, and to bears of the opposite sex. Males were especially interested in female bears in oestrus.
The researchers also examined the feet of polar bears and found prominent sweat glands within the paws of two females. Other mammals are known to use similar sweat glands to communicate information about their territory and sexual or reproductive status. It may also be that the bears use their feet to tread urine into the ground and ice, marking their trails that way.
Together, the results suggest that polar bears use their smelly feet to communicate information about themselves to other bears, especially at certain times of year.
If true, the discovery means that polar bears communicate differently to other bears, which mark vertical objects such as trees, rubbing their bodies or anal glands to lay down scent. Few similar features occur in polar bears' natural habitat, which is dominated by barren ice. It seems the bears overcome this by leaving trails of scent behind as they walk.
The finding offers another reason why polar bears might struggle in a warmer world. If the sea ice becomes more fragmented as a result of climate change, it may make it harder for the bears to leave continuous scent trails and find each other.