The Denver Zoo's polar bear, Cranbeary, snuggles up behind her mate, Lee.

(Photo: Courtesy of Denver Zoo)

It's very difficult to learn if polar bears are pregnant. They don't really "show."

Ultrasounds are often ineffective. And, of course, zookeepers are reluctant to get too close to a giant carnivore.

To learn whether its polar bear, Cranbeary, is pregnant, the Denver Zoo has turned to a beagle named Elvis. He is trained to sniff a bear's poop and, for reasons that are still a mystery to scientists, detect if a bear is pregnant.

Colorado Matters host Ryan Warner speaks with Erin Curry of the Cincinnati Zoo, who's involved in the research.

Elvis the beagle sniffs polar bear poop to detect if the bears are pregnant.