Black Bear Biology & Behavior

American black bears are the most numerous of all the bear species of the world, occurring in habitats across North America with a population estimate of around 25,000 widely distributed throughout Washington State. Not only are they found exclusively in North America, black bears are the only living bear species to have evolved here.

Ecological Roles of Black Bears

Black bears reside in temperate rainforests, dry eastern slope woodlands, neighborhood greenbelts, and anywhere they can find forest cover and plentiful food from sea level to 10,000 foot elevations. Their habitat is characterized by thick forested areas and understory vegetation with an abundant supply of fruit and nut-bearing trees and shrubs. Black bears play an important role in forest ecosystems as seed dispersers and nutrient providers. Berry seeds pass through the bear unbroken and are able to germinate. Not only that, but the seeds come with their own pile of fresh manure as fertilizer!

Short, curved claws make black bears excellent tree climbers. In contrast, grizzly bear claws are much longer, more blunt and are used primarily for excavating food from their preferred open country and high mountain meadow habitats. Grizzly bears, although not adapted primarily for tree-climbing, can still climb any tree you can climb!

Their claws are also well-suited for tearing apart snags and logs and digging up forest duff where they encounter food such as insects and their larvae, small rodents and amphibians. This foraging behavior helps the decaying process in the forest and the return of nutrients to the soil. They are primarily opportunistic omnivores, travelling about their territories, up to 100 square miles, in response to the seasonal availability of food.

Black bears have excellent memories and their sense of smell is unparalleled – more than seven times greater than a dog. They spend their days learning about particular foods and developing their memory about where they can be encountered. Some individual bears have been known to so finely tune their knowledge of where garbage cans are located, that they actually learn the days and routes used by garbage haulers.

In the temperate rainforests found in the coastal watersheds of the Pacific Northwest, migrating salmon comprise a substantial part of the black bear’s diet. In fact, black bears provide essential ecosystem services in these watersheds. Foraging bears transfer large numbers of salmon (eight bears transferred 3100 salmon in one study) from the stream into the riparian zone, leaving the remnants of the decomposing carcasses fixing much needed nitrogen into the soils of the Northwest Coast. The nutrients provided by the salmon are taken up by the root systems of giant coniferous trees, such as Sitka Spruce, and researchers have discovered that the marine-derived nitrogen from salmon contributes substantially to the size, health and vigor of these trees and the surrounding forest community.

During the fall and prior to hibernation all bears enter a physiological phase called hyperphagia, a term that literally means “excessive eating.” Foraging up to twenty hours a day during the autumn months, black bears increase their body weight by thirty-five percent in preparation for winter hibernation. While black bears prefer their native foods, easy-to-access anthropogenic (human-provided) food sources are extremely tempting. Accessing garbage requires little energy expenditure with the payoff being concentrated, nutrient rich, calorie-packed food.

Black Bear Dens and Hibernation

Do black bears hibernate? The short answer is yes. Although there has been past scientific debate about whether or not one of the world’s most famous “hibernator” actually does so, black bears are able to survive severe weather and annual winter food shortages by denning and hibernating during those winter months.

While in hibernation, black bear heart rates typically drop very substantially from 40 – 50 beats per minute down to 8 beats per minute, and there are other beneficial physiological changes which help them maintain this prolonged state of torpor, but their body temperatures do not drop significantly. Unlike other hibernators, black bears are dormant, but don’t need to wait to bring up body temperatures – and thus can awaken and arouse quickly. This condition allows bears to defend themselves and their cubs more effectively should an outside predator disturb them in the den.

Bears hibernate for varying lengths of time depending on where they live and will even occasionally emerge from their dens for a period during the winter. In warmer climates a bear might spend just a few weeks denning, or sometimes not den at all. In Washington and Idaho, black bears den for an average of around 5 months each winter.

Black bears most often choose to den under large boulders, simple depressions under brush, in tree cavities above ground or at the base of a tree, under logs, or even buildings. Compared to grizzly bears, black bears tend to den at lower elevations and in less steep areas than their grizzly bear cousins.

Bears burn fat while in the den and produce usable by-products such as water. The kidneys release less waste than during active times of the year, and the small amount that is created is reabsorbed through the bladder wall. The urine is essentially recycled internally and then is converted to carbon dioxide, water and ammonia. Bears do not defecate while in hibernation.