SUMMIT COUNTY - Bears are emerging from their long winter naps throughout Colorado, and the Division of Wildlife is reminding residents and visitors to always be "bear aware."
At this time of year, bears are looking for new plant growth and fresh grass to eat to help them restart their digestive systems. But once they are up and running, bears are opportunistic feeders and will exploit any available food supply, including garbage, pet food, bird seed, and home and restaurant table scraps. Bears that become habituated to human food sources can be dangerous and often must be euthanized.
Because they are large omnivores, bears are nearly always on a search for food. Wild foods are essential for bears -- berries, insects, acorns, plants and carrion. But when people fail to store garbage, pet food or bird feeders properly, bears will find those sources and cause conflicts in residential and business areas.
In Colorado, bears are ubiquitous from the Front Range across the Western Slope. Although sightings of grizzly bears are reported on rare occasion in the Centennial State, North American black bears (Ursus americanus) are the only bear species known to have established Colorado populations. Their preferred habitats are areas with aspen trees and oak brush.
Bears' dependence on adequate nutrition prior to the denning season drives their whole life cycle, according to John Broderick, terrestrial wildlife program manager for the Colorado Division of Wildlife. Insects and plant material comprise more than half a bear's diet. Particularly important are fruits from plants in the Prunus genus, which includes choke cherries, apricots, serviceberries and raspberries. In the fall, bears eat as much as possible to store fat in preparation for months without food during the winter.
"In late summer and early fall, they're eating machines all the time," Broderick said. "At that time, they're really going to slam themselves with caloric intake to withstand the rigors of denning. We need 1,500 to 2,000 calories a day to stay alive. Bears will bring down 20,000 calories per day."
Spring weather can be a major factor in the frequency of bear-human interactions during the fall: Late spring freezes that kill Prunus flowers lead to decreased fruit production, sending bears searching for other sources of calories during their hungriest times.
Many people confuse or conflate the concepts of "denning" and "hibernation." Denning describes bears' behavior of settling down into a den - a cave or hollowed-out root ball, for example - for the winter. Hibernation, on the other hand, is a physiological response to lack of food, in which the animal's metabolism drastically slows, allowing its body to ration its stored energy (fat) over the course of its winter fast. During hibernation, a bear's heart rate will drop as low as 15 beats per minute.
Bears in captivity that are fed regularly throughout all seasons will not hibernate, although zoo biologists do mimic natural conditions by halting feeding in the fall. Hibernation varies in timing according to a bear's region, age, sex and reproductive status. The process begins in mid-October, and almost all bears are in hibernation by the first week of December.
"Their bodies have evolved in concert with the natural ecology of where they exist," Broderick said.
Julie Sutor can be reached at (970) 668-4630 or firstname.lastname@example.org.