American Black Bear

Characteristics

Rump higher than shoulder with prominent ears. Usually black with a brown muzzle, however can be colored cinnamon, dark brown, or blonde and in small areas in British Columbia or coastal Alaska, white or blue-gray, respectively. Profile of muzzle will be straight or convex, as opposed to the brown bear that have concave muzzles.

Species Specifics

There are 16 subspecies proposed, 2 in CA. Their closest living relatives are Asiatic black bears (polar and brown bears are close relatives to one another; black bears are separate).

Physical Characteristics

Black bears have smaller claws than brown bears because they are adapted more for climbing than digging. They have the ability to slow their metabolic rate down yearly in the winter for hibernation (though some southern black bears only sleep for a few days). They enter a 'walking' hibernation first when they are alert but do not eat or drink often, then body systems slowly slow down until they stay in their chosen den. Their heart rate is 40-70 bmp during the summer and slows to 8-10 bmp during hibernation. They can be roused easily from hibernation, hypothesized as an adaptation for emergency situations (such as earthquakes). They can also change dens up to 4 times during hibernation and awaken during warm spells.

Ecology

Habitat

Habitat Type: Primarily temperate and boreal forests as well as swamps

Distribution

Home range sizes vary depending on the ecosystem, but the average for females is 4.6-19.3 square miles and 45.2-77.2 square miles for males. Mothers have been known to lead cubs on treks of up to 60 miles from their home ranges to show cubs seasonal food (such as special berry patches or a salmon run).

Diet

Generalist, opportunist omnivore. Vegetation, roots, buds, fruits, nuts, insects, vertebrates (from fish to mammals) including carrion. Seasonal Diet: In early spring, their diet includes herbs, buds, young leaves, occasionally carrion, or nuts left over from the previous fall. Later, they add insects and young deer and moose. By summer, berries and nuts are their main food source (they can eat tens of thousands of nuts or berries each day). In certain areas, especially where grizzlies are absent, they eat a lot of fish. Also consume human food or trash at any point. They eat 11-18 lbs. of food per day and can double their weight prior to hibernation.

Ecological Web

This species is very important to ecosystem structure due to their omnivorous, opportunistic nature. They act as scavengers removing diseases from the ecosystem, as predators, as prey on occasion, and they play an important role in returning nutrients to soil. All of these roles combined help to increase species diversity where they are found. Predators: Adult bears are considered apex predators but wolves and brown bears have been noted killing them. Cubs are frequently are killed by wolves, brown bears, coyotes, bobcats, lynx, and mountain lions and 1.5-year-old males are often killed by wolves, mountain lions, and hunters.

Activity and Behavior

Activity Pattern

Typically diurnal, but can be crepuscular. This is possibly to escape midday heat in warm environments and/or by human activity. Can also be seen active during the night. In the summer, because they need to increase weight for the winter, they need to spend almost 20 hours a day eating, an average of one berry per second.

Behavior

Have an unaggressive nature, which has led to more human tolerance. With this, they have been able to obtain more human-related food, which is easier for them to find and generally has a higher calorie count. Now they can mature faster and produce more offspring, which has lead to an increase in their overall population. Mothers eat their cubs' feces in the den to keep the den clean and so the smell is not an attractant for predators. They communicate territories via scent-marking (with urine and feet) and rubbing, clawing, or biting tree trunks.

Social Behavior

Solitary, though males' ranges generally overlap with several females. Come together during estrus, and females take care of cubs for long periods.

Reproductive Behavior

Mating usually occurs in May-July, but the uterine implantation of blastocysts occurs in November, with birth in January (during hibernation, so the female partially wakes). Females in estrus will travel throughout their territories more often to increase chances of finding a mate, and males' ranges generally overlap the range of several females. During the middle of her estrus period (3-5 days) she will allow copulation; which is generally 30 minutes but can be up to an hour. For these few days, the male and female will feed and sleep together, and copulate frequently. Infanticide can occur; males kill females' cubs to copulate with her to ensure his genetic survival.

Offspring

2-3 cubs are most common, but 5-6 occur as well. Cubs generally stay with their mother for ~17 months. If females have only 1, they can abandon it (a female that stays with 1 cub for over 1 year ends would have fewer total young overall than if she abandoned the single cub and produced 3 the following year). Generally, they have offspring every 2 years.

Conservation

Status

Least Concern by IUCN, CITES Appendix II. In CA, considered game mammal. Population Trend: Increasing

Historical

The American Black Bear is the smallest of the three bears species found in North America, and are found only in North America. Black bears have short, non-retractable claws that give them an excellent tree-climbing ability. Though they are called black bears, their fur can be more colors than any other North American mammal: black, brown, cinnamon, blond, blue-gray, and even white. Cubs stay with their very protective mom for about a year and a half. She nurses them, protects them and teaches them until they are ready to be strong, independent bears. Black bears face incredible human-wildlife conflict when living near humans, mostly due to people not properly taking care of their food waste. When bears become doo habituated to humans, they are at risk for depredation. While Black Bears have no natural predators, habitat loss and hunting are other challenges they face.

Current Threats

Our Role

Oakland Zoo supports the Bear League. Based in Tahoe, the Bear League educates the community and beyond on how to live sustainably with Black Bears, responds to bears in human territory, rents the bear scare mats and facilitates a 24 hour hot line for bear sightings and encounters. Oakland Zoo sponsors the Bear League's "scare mats" that are affordably rented by the public to place in front of windows and doors where bears are entering a home or establishment. This alters bear behavior, sending them back into the wild.