Heat Loss in Dens

In 2003, the BBC phoned researchers for help with a documentary using new thermal imaging technology. The telephone conversation sounded something like:

BBC: “We’re looking for someone dumb enough to try putting tiny cameras under a mother black bear with cubs in a den. Do you have such a person?”

Researcher: “Will it have educational value that we can use at the Bear Center someday?

BBC: “Yes. One of the cameras will make the very first thermal images of heat loss patterns in dens.”

Researcher: “We have just the person.”

In the first week of February, the BBC and the researcher went to the den of 3-year-old Dot. The researcher crawled into the den, showed Dot the camera, and gently eased it underneath her, revealing cubs less than 2 weeks old.

The camera was connected by cable to a monitor 30 feet away. A BBC producer watched the monitor and told the researcher where to aim the camera—up, left, hold steady, etc.

In early April, the team filmed the bears again shortly before they emerged. At one point, the researcher momentarily stepped away from the den during a blizzard and returned covered with snow. When he started to enter the den, the mother didn’t recognize him and lunged. The researcher spoke and offered his hand for her to smell. The nervous mother relaxed, lay back down, and even lifted a leg as he put the camera under her again.

Narrated by David Attenborough, the documentary shows heat loss to be especially great from the eyeballs, nose, and forehead. This helps explain why bears tuck those parts under the chest when they curl up on their stomach in the hibernating position. The main area exposed is the thickly furred back.