Black bears in Colorado primarily live in areas dominated by aspen and oak brush habitats. Some bears never leave oakbrush zones while most venture into aspen communities. High spruce-fir forests are not very good bear habitat. Black bears are omnivores, eating both plant and animal material and are day-active, opportunistic feeders. Roughly 90% of a bears’ diet is made up of vegetation. Black bears know their home, seasonal and annual ranges very well and are keenly aware of micro habitats that hold an abundance of food sources. They will migrate great distances to various seasonal food areas. Adults have a home range of 10 to 250 square miles.
After emerging from dens in the spring, bears travel to lower elevations to feed upon green-up – highly digestible, fresh, young vegetation. Preferring aspen habitat at this time, they are consuming 2,000 to 2,500 calories a day, feeding on anything from grasses, flowers, leaves, roots, ants and larvae, beetles, elk calves and deer fawns, baby birds and animal carcasses. Black bears will typically forage for two to four hours during much of spring and summer, compared to 20 hours of active foraging during the fall hyperfagia feeding phase. Some examples of vegetation that bears feed on in spring and summer months include loveroot, waterleaf, angelica, peavine and meadowrue. See photo examples of spring and summer bear foods.
Bears, like us, have a simple, one-chambered stomach digestive system not good for digesting cellulose. Young, fast-growing, succulent grasses and forbs contain less cellulose and can be as high as 20% to 30% protein. As these plants mature their protein content falls to around 3 to 4 percent.
As grasses and other vegetation begin to dry up and lose their nutritional value, many bears will head for higher elevations where moisture allows vegetation, cow parsnip for example, to stay viable. Those that linger at lower habitats will feed on squawapple, serviceberry and the like.
hyperphagia: a period of excessive eating and drinking to fatten for hibernation
In late summer the vast majority of black bears will migrate to oak brush habitats the middle of August in search of berries and acorns, often migrating 20 to 30 miles from their summer range to traditional fall ranges. During this fall hyperphagia (feeding frenzy) phase, if the food supply is there, bears will:
- Feed up to 20 hours a day
- Consume 20,000 calories
- Add two to four pounds of fat
– each day to build up enough fat reserves to get thru the five to six months of food-less hibernation.
They may eat 20 to 30 pounds of berries and acorns daily. For reference, it takes 1,500 chokecherries to make a pound. Bears feed on grasses throughout the year, but favor other foods in the fall. In years of good production, bears will bypass mostly all other natural foods in favor of acorns. Some examples of foods that bears rely on in the fall include elderberry, hawthorn, chokecherry, serviceberry, wild rose hips and most importantly, acorns. See photo examples of fall bear foods.
If their usual natural food sources are scarce, they will search for alternative food, which often brings them into conflict with people.
20,000 calories is roughly equivalent to eating 30 Burger King Whoppers or 95 Taco Bell soft tacos.
Banner photo by John Viner
Bear migration GPS mapping courtesy: Sharon Baruch-Mordo, Aspen Black Bear Ecology Study