Black Bear Biology & Behavior

Black Bear Behavior

Black Bear in tree Photo

Black bear image from Bear Smart Durango

Bears may forage up to 20 hours a day during autumn, increasing their body weight by 35% in preparation for winter. During this time they enter ‘hyperphagia’, which literally means “excessive eating.”

Black bears move in response to the seasonal availability of food and have excellent memories, particularly regarding food sources. Bears are able to learn about food types and locations, and reapply that knowledge over time and space – a sure sign of intelligence.

Black bears can run 25 to 30 mph and, contrary to some myths, can easily run up and down hill.

Black bears have good eyesight which is comparable to humans, and very good hearing. Their sense of smell is unparalleled – seven times greater than a dog. The black bears short, sharp claws evolved for climbing trees which they do to escape  predators, find food, sleep and rest.

Black Bear Reproduction and Maturation

Black bear females do not reproduce until they are three to five years old but some may be as old as seven. Females normally breed every other year and have an average of two cubs, but can have one to five. Cub mortality is high, with an average of 50 percent dying in their first year due to natural causes. The female has 6 nipples and produces milk that is exceptionally high in fat, hence the cubs’ rapid growth.

Black Bear Cubs

Black bear cubs. Photo by Rich Beausoleil WDFW

Females conceive during the summer (mid June to July in Washington) and gestation is 7 to 7 1/2  months. However, impregnated females go through a process called delayed implantation so development of the embryo does not begin until November or December.  Cubs are born two months later, in January or February weighing just 225 to 330 grams and measuring about 8 inches long. The cubs are blind and deaf, have poorly developed hindquarters, and are covered with a fine down-like hair. They suckle frequently from the female in the den and emerge with her in the spring. They remain with the female for 16 to 18 months during which time she teaches them everything they need to know to survive.

The female does not mate while rearing young, so may only produce six litters in her lifetime.

The average lifespan of a black bear is 18 years, and the oldest documented wild bear lived to 31. During their lives black bears can suffer from arthritis, cavities, fractures from falls, broken and worn teeth, bites from other animals and gun shots.

Black Bear Diet

Black bears are omnivores, meaning they eat both plants and animals. Eighty to eight-five percent of a black bear’s diet is plant material, while the remaining 15% is made up of animal protein. Black bears will eat almost anything, such as grubs from a bumblebee nest, bird eggs, ants, voles, grasses and berries.

Black bears are also opportunistic, meaning they take advantage of whatever is available.  They will occasionally eat carrion when available and will hunt and kill their own prey including calves of elk, moose and deer. They also scavenge meat from winter-killed animals, dig for rodents, and eat termites, ants, grubs and other insects.

A bear’s diet changes seasonally. In spring, bears eat the tender shoots of grasses, cow parsnip, leaf buds and skunk cabbage. Bears have the digestive system of a carnivore so cannot digest firm plant cellulose well. They target many plants in the spring when young shoots are most digestible and nutritious.

Bear eating berries. Photo courtesy of Bear Smart Durango

Cinnamon black bear eating grass. Photo by Ron Coscorrosa

 

Black bears will sometimes eat the sugar-rich cambium layer under the bark of coniferous trees, and can kill the tree in the process. During summer months bears begin to re-focus their attention on berries – an essential diet item as the bears begin to prepare for winter sleep. In the fall, in some parts of the black bear range, nuts become another important part of a bear’s diet. Acorns, white bark pine nuts, and hickory nuts are a few favorites. Black bears are known to raid the caches of squirrels to get to the nuts they have stored for the winter. In the West, salmon represent an important food source for black bears.

Salmon berry. Photo by Ron Coscorrosa

Bear scat. Photo by Rich Beausoleil WDF

 

Black Bear Habitat and Territory

The home range of a female black bear is generally 2.5 to 10 mi2 (6.4-25.9 km2). Male black bear home ranges are 10 to 59 mi2 (26-152 km2). Female black bears generally will not share their territory with other females, but the ranges of several males may overlap.

Black Bear Dens and Hibernation

Black Bear Den

Black Bear Den. Photo by Rich Beausoleil WDFW

Black bears do not truly hibernate, they den. Denning black bears enter a state of ‘torpor’, a modified form of hibernation. Their heart rate typically drops from 40 – 50 beats per minute to 8 beats per minute, but their body temperature does not drop significantly. This drowsy-but-ready condition allows bears to defend themselves and their cubs more effectively should a predator disturb them in the den and the bears will occasionally emerge from their dens in winter.

Bears den for varying lengths of time depending on where they live. 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.

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.

Black Bear Communication

Black bears emit a variety of vocalizations to communicate with other bears and other species. Along with vocalizations, bears use posturing to communicate dominance or subordination, and to express attitudes. Visit the North American Bear Center to read descriptions of black bear cub vocalizations to their mothers and to listen to audio files of black bear vocalizations.

In order to establish dominance, male black bears will often claw trees, with the highest marks on the tree associated with the most dominant male.

Two often-misinterpreted forms of black bear communication that can put a hiker on edge are bluff charges and a bear standing upright on its hind legs. Bluff charges are far more common than actual attacks, and are used to scare off a potential threat. They are generally broken off a few feet away, sometimes accompanied by stamping on the ground. A bear standing on its hind legs is simply trying to get a better look with its mediocre vision.

Ecological Roles of Black Bears

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!

Black bears also break up downed logs in their search for grubs, helping the process of decay in the forest and the return of nutrients to the soil.

Threats to Black Bears

Black Bear Threats

American black bears adapt well to human development, and their global population is estimated to be twice that of all other species of bears combined.  Their population in Washington State is estimated to be as high as 30,000, and they are found in nearly every county in the state.  They are classified as a game animal and harvest numbers can reach over 2,000 per year.

While the overall population is strong and not threatened at this time, individual bears often come into conflict with humans.  Because of their adaptability, they can live in close proximity to human development.  Particularly in years when the local berry crop fails, they will frequent municipal garbage dumps and household garbage cans looking for food.  Once they become overly habituated or begin to be seen as a threat to people or pets, they can be relocated or even killed by the wildlife authorities.

As more housing developments and roads are built on the fringes of the urban areas in western Washington, black bears are losing habitat, and opportunities for them to pursue their natural food sources are becoming even more limited.  This is already resulting in increased interactions between black bears and humans.  As climate change shifts the distribution of their food sources, conflicts are likely to increase as they seek out new, suitable habitat.  A large network of interconnected, wild lands would reduce the risk of conflict.