Wild Colroado: Warm weather postpones hibernation
November 10, 2012
Normally Summit County bears transition into hibernation in early October, but with this unusually slow start to winter, the long nap is getting postponed.
Black bears in the area, though a handful of them have started their hibernation, are still active throughout Summit County neighborhoods, primarily in Breckenridge and the Blue River area in Silverthorne.
“I can definitively say that there are some bears in the area that have gone into hibernation,” said Sean Shepherd, wildlife biologist with Colorado Parks and Wildlife. “But we’ve still been getting reports of bears active in town – I’m surprised to hear that there are still bears out and about.”
In a typical year, bears in the area transition into a “denning” phase and hibernation in early October, but with the warm weather and lack of snow, the local ursines are taking their time with the transition, according to Shepherd.
It’s the human food source too, that is sustaining bears longer this season.
“This was not a good year for natural food sources in Summit County, but the bears are able to supplement their diet so heavily with human trash,” Shepherd said.
The local bears’ dependency on human trash may be keeping them more active longer, but as cooler temperatures and snow begin to accumulate, it’s inevitable that they will transition to preserve energy and caloric waste.
While a bear is in the denning phases, it is less active due to lack of food sources and will be moving closer to areas of hibernation.
A bear requires its winter den to be insulating and away from predators and human traffic, thus wintering areas are farther into the backcountry, according to Shepherd.
Once a bear is in its hibernation state, it can go for as long as 100 days without eating, drinking, urinating, defecating, or exercising, according to wildlife officials.
Preparations for over-wintering begin in the summer, when bears begin gorging carbohydrate-rich berries and other foods to put on weight.
During this period, they can gain as much as 30 pounds per week. In early autumn, a bear – and its cubs, if it has any – will rake leaves, twigs and other plant materials into the den to form a nest, according to a study by Colorado State University.
Throughout the fall its activity level steadily drops until it ends completely when the bear enters its den.
Normally, by November, bears are well settled into their dens, not to emerge until late April, Shepherd said. Currently the population in Summit County is in limbo: The weather is depicting an early fall climate. Without dropping temperatures and snow bears are without a cue to check into their long, winter nap.
Bears make dens in burrows, caves, hollowed-out trees and rock crevices. Dens of bears typically feature entrances just large enough for a bear to squeeze through, with interior chambers measuring up to 5-feet wide and 3-feet high.
Once hibernating, a black bear can doze for many months with a body temperature of 88°F or higher, which is within 12°F of summer levels.
By contrast, the body temperature of smaller hibernators such as marmots, chipmunks and ground squirrels may drop below 40°F.
These daintier creatures must awaken every few days, raise their body temperatures to summer levels, eat stored food and pass waste, but bears are able to stagnate longer with their high body temperatures.