A New Threat to Polar Bears Makes It Hard for Them to Find Mates

The scent markings the animals leave to lure partners are disappearing with their sea ice habitat.

(Photo: The Asahi Shimbun via Getty)

Nov 10, 2014· 1 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

Polar bears can smell their way to love. The animals leave scent markings—made either by sweat glands on the bottom of their feet or by urine—to find other bears looking for a love match.

But all that could be changing as a warming climate melts the ice habitat the bears depend on for their survival.

The problem is that the animals, which maintain the largest range of any bear species, must deposit their scent over a huge swath of icy terrain to get the chemical message across to potential mates. One satellite-tracked female, for instance, trekked more than 3,000 miles in a year.

To test how so-called chemo-signaling affects bear behavior, researchers at the San Diego Zoo’s Institute for Conservation Research and other institutions spent five years sampling scents left behind by 300 wild polar bears living around the southern Beaufort Sea and the Chukchi Sea in the Arctic Ocean. To obtain the scents, the scientists swabbed between the toes of sedated male and female bears, testing them during different seasons.

They used that smell to entice 10 adult male polar bears and 16 adult females living in 10 different zoos across the United States with the scents. Each scent was smeared onto a piece of cardboard encased in a box.

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They found that female bears were more interested in the boxes in the spring breeding season, while males were equally interested in spring and fall. When the zoo-living males smelled the scents of females in heat, they displayed mating behavior, according to a study published in the Journal of Zoology.

Megan Owen, a researcher at the San Diego Zoo, said she was interested in the question because scent communication in solitary species hadn’t been investigated much—even though it’s crucial for some animals’ survival.

“Being able to identify, find, or avoid members of your own species is essential for successful reproduction,” she said. “Because polar bears are wide-ranging, seasonal breeders, the potential for communication disruption to have biologically significant impacts is greater.”

When ocean ice breaks up, as is happening in the Arctic environment where the bears live, it makes it more difficult for the animals to find one another. While the researchers haven’t yet directly observed this scent communication breakdown, Owen said it is likely happening.

She said her team plans to follow up with a study to chemically analyze the scents collected in Alaska and refine their understanding of the information polar bears gain from such smells.