Ursus americanus - American Black Bear

Skull Pictures:     
Dorsal      Posterior mandible
Lateral     Ventral
Mandible

Physical Description:

Black bears are the third largest mammal in Wisconsin, with elk (Cervus elaphus) and moose (Alces alces) the only larger mammals. They are the commonest, most widely distributed and smallest of the bear family Ursidae.

Black bear coats are usually black in color, but can range from black to dark brown. A tan muzzle is prevalent, and about 25 percent of bears have a whitish, V-shaped throat patch (Kurta 1995).

       Black coat                                                        Brown coat

Adult male’s average 1,200-1800 mm (47-70 in) long and weigh between 110-160 kg (250-350 lb). Adult females, although smaller, average 1250-1500 mm (50-58 in) long and weigh between 55-81 kg (120-180 lb). Adults average 610-920 mm (24-36 in) at the shoulders. A recorded weight of 315 kg (700 lb) occurred in a Wisconsin black bear (WDNR 2003c).

The eyes are small relative to the head, and the ears are short, rounded and erect. Each foot has five toes, each equipped with a non-retractable claw. The tail, which is almost concealed in their fur, ranges in length from 80-125 mm (3-5in) (Kurta 1995).

The black bear can be easily distinguished from the brown bear (Ursus Arctos). The black bear does not have a muscular hump behind shoulders, less concave muzzle, rounded forehead, and is much smaller (Burt 1980). Also, the claws of a black bear are much shorter and curved, there is little to no gap between the footprint and claws (Northwest Territories 2001).

There are 16 recognized subspecies of black bears; the Wisconsin subspecies is Ursus americanus americanus (Synder 1991).

Distribution:

Current Distribution-

The 2003 Wisconsin black bear population is estimated at 11,150 (WDNR 2003a).  The following map was obtained from the WDNR, and shows the current distribution of black bears in Wisconsin. The map illustrates primary, secondary, occasional and rare ranges of the bear. They are most common in the northern third of Wisconsin, with about one bear per 10.4 square kilometers (4 square miles).

Figure from WDNR (2003b): http://www.dnr.state.wi.us/org/land/wildlife/hunt/bear/popndist.htm

Historical Distribution-

Historically, before European settlement, black bears inhabited most of the forested regions of North America, including the entire state of Wisconsin (Hall 1981). Before 1985, uncontrolled limits and increasing harvests caused the bear population to decline. After a closed season in 1985, a new system of bear hunting and harvest control was enacted in the 1986 season. Since then, the bear population in Wisconsin has increased steadily to a healthy population (WDNR 2003b).

Ontogeny and Reproduction:

Bear life cycle-

 Born in a winter den, at birth a healthy cub weighs between 7-12 ounces. Cubs are born relatively helpless, as noeonates, the eyes do not opening for 25-30 days and they are lightly furred. Along with being blind and cold at birth, the mother is usually asleep, but they instinctively make their way to the mothers milk supply. Emerging from the den in spring with their mother, they will begin to eat solid foods in about two weeks.

Although a cub is weaned in September of their first year, they will remain with their mother and share the wintering den.  In the following spring, they will disperse or the mother will chase them off to stop inbreeding from occurring. If the cub survives the year, it has an excellent chance of living a long life.

Black bears reach sexual maturity at 3.5 years old. Females are ready to mate at this age, but males tend to mate at 4-5 years old. Females may not successfully raise a litter of cubs until the age of six or more (Weber 1994). Breeding occurs in June to mid-July. Boars (male bears) are drawn to the scent of a breeding female about a week before she comes into heat, giving the pair time to get acquainted with each others presence.

They exhibit delayed implantation, meaning that the embryo does not implant in the uterine wall of the sow until winter dormancy begins. If a female is sickly or unable to put on enough fat needed for denning, the pregnancy is spontaneously aborted.

A female black bear will normally give birth to 2, but occasion 1 or 3, with a reported maximum of 6 cubs. Gestation is relative, at about 7-7.5 months (Burt 1990).

Bears have an average life span of 10 years in the wild; can reach up to 30 years. They reach maturity at age 5-7, but can happen at age 3. Premature death of adult bears is usually human related, in young; it is from malnutrition (Kurta 1995).

Predators-

The short list of black bear predators consists of humans, grizzly bears (U. arctos), and other black bears. Coyotes (Canis latrans) may prey upon cubs (Snyder 1991).

Ecology and Behavior:

Nutrition-

Although black bears are in the order carnivore (carnivores), they are an omnivore. Even though they possess large canines, the carnassial pair is poorly developed and takes a more bunodont shape, for grinding and crushing fruits and insects. Only about one-quarter of their diet is of animal food (Kurta 1995).

Plants and insects are the most important food items in a bears diet (Payne 1998). Kinds of fruit eaten include raspberries, blueberries, strawberries, blackberries, cranberries, strawberries, apples and cherries. They rip open rotting logs, overturn rocks and dig in the ground searching for invertebrates. And occasionally eats fish, rabbits, mice, and, rarely a deer fawn.  

Behavior-

Black bears are primarily nocturnal (crepuscular), and occasionally seen during any part of the daytime. They are solitary creatures, but frequently over lap home ranges of neighboring bears. Although female bears with cubs will go out of the way to avoid male bears, because a mature male will sometimes kill the cubs of a female to bring her into estrus.

Ecology-

The dormancy for which they go into was coined “carnivorean lethargy.” The heart rate declines from 40 beats/minute to 10 beats/minute, and body temperature falls from the normal 38oC (100oF) to 33oC (91oF) during lethargy (Kurta 1995). Bears need to gain about 50-60 pounds of fat to sustain them through this dormancy. This lasts from 4-7 months, and can be longer in colder climates.

Black bears prefer forested and shrubby areas but will inhabit wet meadows, riparian areas, burned areas, ridge tops and swampy hardwood and conifer forests. In the spring they seek southerly slopes in lower elevations for forage, then gradually transition to higher elevations on northerly and easterly slopes as the summer progresses.  They use dense cover for hiding, thermal protection, and bedding. They climb trees to escape from danger (Snyder 1991).

Home range for an adult male differs greatly then that of an adult female. The home range for an adult male averages 20,000 to 35,000 acres. An adult female’s home range is considerably less, averaging 4,200 to 7,800 acres (Koehler 2003).

Economic Importance:

Positive-

Black bears in Wisconsin are treated as game animals with regulated hunting. In 2002, 2,437 black bears were harvested in Wisconsin (WDNR 2003b). They are hunted for meat, cloths, rugs and trophies.

Negative-

Some black bears take the easy way out in obtaining food, and therefore are termed “nuisance bears.” These bears will raid garbage cans, campsites and the town dump looking for an easy meal. Although they are usually harmless, these bears may be ill of injured and should be avoided. Some bears become such “nuisance bears” that they must be relocated or exterminated.

Remarks:

Bears can run up to 30mph for short distances.

They are also great climbers and swimmers.

Neartic, which means they are located in the region of plant and animal life in the Arctic and temperate areas North America

Literature Cited:

Burt, W. H., R. P. Grossenheider. 1980. Third edition. Peterson Field Guides: Mammals. Houghton Mifflin Co., Boston, New York

Hall, E.R. 1981. The mammals of North America. 2nd ed. John Wiley and Sons, New York. 1,181 pp.

Koehler, G. M., and D. J. Pierce. 2003. Black bear home-range sizes in Washington: Climatic, Vegetative, and Social Influences. Journal of Mammalogy 84:81-91.

Kurta, A. 1995. Mammals of the Great Lakes Region.University of Michigan Press, U.S.A.

Northwest Territories: Resources, Wildlife, and Economic Development Division. 2001. "Encountering Bears." Available (December, 2003)
http://www.nwtwildlife.rwed.gov.nt.ca/Publications/safetyinbearcountry/encounters.htm .

Payne, N., B. Kohn, N. Norton, and G. Bertagnoli. 1998. Black bear food items in northern Wisconsin. Transactions of the Wisconsin Academy of Sciences, Arts, and Letters. 88:263-280.

Snyder, S. A. 1991. Ursus americanus.  <http://www.fs.fed.us/database/feis/animals/mammal/uram/index.html>.

WDNR 2003a. 2003. 2003 Black Bear Forecast. Accessed on December, 2003.  <http://www.dnr.state.wi.us/org/land/wildlife/hunt/seasforc/bear.htm>.

WDNR 2003b. 2003. Black Bear Population and Distribution. Accessed December, 2003.  <http://www.dnr.state.wi.us/org/land/wildlife/hunt/bear/popndist.htm>.

WDNR 2003c. 2003. The Black Bear. Accessed December, 2003.  <http://www.dnr.state.wi.us/org/caer/ce/eek/critter/mammal/bears.htm>.

Weber, K. T. 1994. Analysis of black bear habitat in northern Wisconsin. Transactions of the Wisconsin Academy of Sciences, Arts, and Letters: 82.

Reference written by Sayer Larson, Biol 378.  Edited by Christopher Yahnke and Jen Callahan.
Page last updated 5-7-04.