Eli licks snow off Lily This morning before 6 AM, Lily was breathing a steady 5 breaths per minute and this afternoon at 4:43 PM a steady 4.75 breaths per minute. Both were higher than her 4.1 breaths per minute 2 weeks ago on April 3. Snow filtered into the den and coated Lily's back today—evidence that the cubs antics are taking a toll on the integrity of the den! They helped out by licking the snow off.
Cub and LilySame story for Jewel, breathing 5 times per minute as compared with 3.1 on January 2 this year and 4 times per minute on December 29, 2012.
We suspect that breathing rates during sleep may roughly reflect oxygen consumption and metabolic rate. 
Lily with microphone and tubeIf so, Lily and Jewel are developing higher metabolisms in preparation for activity. At least, that is our working hypothesis to disprove as more observations refute it or strengthen the pattern. If the pattern shows promise, some curious scientist with captive bears might someday test the hypothesis with an airtight system that allows measurement of oxygen consumption directly over a given period.
Duluth bear - April 15, 2013At a little after 5 PM, Jewel was deep into REM sleep with her eyes fluttering open and her nose and lips twitching in front of the camera. She made it easy to see because she wasn’t sleeping with her head tucked under in the hibernating position.
Playful Duluth bear - April 15, 2013A Lily Fan sent pictures of the big bear that hangs out by its culvert den in Duluth, mostly ignoring people. The bear walks well on crusty snow and appears to have nicely hardened new footpads.
There will be two videos of Lily and cubs today. Part I is available at http://www.youtube.com/watch?v=4aW-VSsLURA. Look for Part II later on at http://www.youtube.com/bearstudy.
Thank you for all you do.
—Lynn Rogers and Sue Mansfield, Biologists, Wildlife Research Institute and North American Bear Center
All photos taken today unless otherwise noted.