Vail Curious Nature: Bears bearing in winter |

Vail Curious Nature: Bears bearing in winter

Natalia Hanks
Special to the Daily
Vail, CO Colorado
Natalia Hanks

VAIL VALLEY, Colorado –Snug in a hollow tree, cave or a shallow nest, black bears in winter in Colorado’s Vail Valley may be dreaming dreams of berries and honey and lush meadows of grass during their hibernation.

But female black bears also have something else on their agenda as they lay curled up, enveloped in thick winter fur. If it is mid-January, then they will probably give birth.

Before their cubs are born, female black bears, or sows, must prepare in order to assure a healthy offspring. They need plenty of food and a safe den.

In the fall, adult bears can spend 20 hours a day eating up to 40,000 calories. The accumulated fat is critical in keeping bears healthy during hibernation and helping sows give birth to healthy cubs and keep them nourished.

Bears are opportunistic and eat whatever they find, including berries, roots, nuts, grasses, insects, honey and carrion. Unfortunately, in populated areas like the Vail Valley, bears can also take advantage of easy calories in garbage containers, at campgrounds and even in our kitchens after getting in through open windows or doors. This confrontation with humans can be deadly for bears.

By late fall, adult black bears can weigh 125 to 600 pounds depending on gender.

The second preparation is securing a winter home. Rarely using the same den year to year, black bears secure a den in a hollow tree, a cave, a tunnel dug into a hillside with their strong muscles and long claws, or even a nest on the leeward side of a large tree. Sows will enlist their yearling cubs to help carry leaves, grass and plants to insulate their den. Lessons learned early in den building are useful for the cubs who will be on their own by age two or three.

Sows will hibernate in dens accompanied by their yearling cubs the first full winter following their birth. This seasonal reduction of activity coincides with a scarcity of food and the onset of cold temperatures.

The start of hibernation varies depending on the abundance of available food in fall. During this state, oxygen consumption and metabolic rate are reduced in half, and heart rate slows down to 8 to 21 beats per minute from a normal 80 to 100 beats per minute. While hibernating, bears will not drink, eat, urinate or defecate. All nutrients are recycled in their body and no waste is produced.

Snug in their dens, sows will give birth every second January to an average of two cubs. Although the gestation period is eight months, embryonic development takes only about two months due to delayed implantation – another adaptation that enables sows to conserve energy reserves during their intense food gathering period.

Newborns are about the size of an apple, hairless with eyes closed and weigh no more than a pound at birth. Newborn cubs are smaller compared to the size of their mothers than any other mammal.

Within two months, the cubs have inch-long hair and can crawl around their cozy den, but they count on their mother’s rich milk for food and her heavy coat for warmth. By spring, they can weigh 20 pounds and are ready to investigate the world outside.

With warmer temperatures in early spring, adult bears emerge from their dens and begin shifting from hibernation to normal function as their metabolic state adjusts to summer activity. Cubs will stay with their mothers for about 18 months, spending one full winter with them in their dens and then will leave prior to the next summer’s mating season, when the two-year cycle repeats.

As you enjoy this January’s full moon – often called the bear moon – know that throughout the valley newborn cubs the size of apples are being born, beginning another wondrous cycle of nature in our mountain home.

The Gore Range Natural Science School’s Curious Nature column appears Mondays in the Vail Daily and on The Gore Range Natural Science School’s Curious Nature column appears Mondays in the Vail Daily and on Natalia Hanks is the director of development at Gore Range Natural Science School where she works to raise funds to support the school.

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