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American black bear

Ursus americanus

What do they look like?

Black bears are usually black in color, particularly in eastern North America. They usually have a pale muzzle which contrasts with their darker fur and may sometimes have a white chest spot. Western populations are usually lighter in color, being more often brown, cinnamon, or blonde. Some populations in coastal British Columbia and Alaska are creamy white or bluish gray. Total body length in males ranges from 1400 to 2000 mm, and from 1200 to 1600 mm in females. Tail length ranges from 80 to 140 mm. Males weigh between 47 and 409 kg, females weigh between 39 and 236 kg.

Black bears are distinguished from grizzly or brown bears (Ursus arctos) by their longer, less heavily furred ears, smaller shoulder humps, and a convex, rather than concave, profile.

  • Sexual Dimorphism
  • male larger
  • Range mass
    39.0 to 409.0 kg
    85.90 to 900.88 lb
  • Range length
    1200.0 to 2000.0 mm
    47.24 to 78.74 in

Where do they live?

Black bears can be found from northern Alaska east across Canada to Labrador and Newfoundland, and south through much of Alaska, virtually all of Canada, and most of the United States into central Mexico.

What kind of habitat do they need?

Black bears are most often found in areas with abundant cover and sources of food. They are usually found in rough terrain with lots of dense forest cover, including swampy areas. They require places to den during the winter, which can be in caves or under large boulders or tree roots. The most critical aspect of the habitat required by black bears is sufficient food supplies, which is why many black bears live successfully near humans.

How do they reproduce?

Males and females meet temporarily for mating when females are in estrus. Male home ranges overlap with those of several females. (Lariviere, 2001)

Males and females coexist briefly during the mating season, which generally peaks from June to mid-July. Females usually give birth every other year, but sometimes wait 3 or 4 years, depending on food availability. Pregnancy generally lasts about 220 days, but this includes a period of time when the egg has not started developing. The fertilized eggs remain in a suspended state until the fall, when embryonic development begins. This development lasts only 10 weeks. Births occur mainly in January and February, while the female is hibernating. The number of young per litter ranges from one to five and is usually two or three. At birth the young weigh 200 to 450 grams each, the smallest young relative to adult size of any placental mammal. They are born naked and blind.

Females reach sexual maturity at from 2 to 9 years old, and have cubs every other year after maturing. Males reach sexual maturity at 3 to 4 years old but continue to grow until they are 10 to 12 years old, at which point they are large enough to dominate younger bears without fighting.

  • How often does reproduction occur?
    Female black bears have cubs every other year if they have enough food to support pregnancy.
  • Breeding season
    Black bears breed in June and July.
  • Range number of offspring
    1.0 to 5.0
  • Average number of offspring
    2
    AnAge
  • Average gestation period
    220.0 days
  • Average gestation period
    70 days
    AnAge
  • Range weaning age
    6.0 to 8.0 months
  • Range age at sexual or reproductive maturity (female)
    2.0 to 5.0 years
  • Range age at sexual or reproductive maturity (male)
    2.0 to 5.0 years

Black bear cubs remain in the den with their sleeping mother and nurse throughout the winter. When the family emerges in the spring the cubs weigh between 2 and 5 kg. They are ususally weaned at around 6 to 8 months of age, but remain with the mother and den with her during their second winter of life, until they are about 17 months old. At this time the mother forces the young out of her territory. They may weigh between 7 and 49 kg at this point, depending on food supplies. Black bear mothers care for their young and teach them necessary life skills throughout the time that their cubs are with them.

Male black bears do not contribute directly to their offspring but do indirectly by preventing new males from moving into the area. This makes it less likely for the young or mother to encounter an aggressive male or have to compete with new bears for food. (Lariviere, 2001)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female
  • extended period of juvenile learning

How long do they live?

Black bears can live to 30 years in the wild but most often live for only about 10, mostly because of encounters with humans. More than 90% of black bear deaths after the age of 18 months are the result of gunshots, trapping, motor vehicle accidents, or other interactions with humans. (Lariviere, 2001)

How do they behave?

Black bears are generally active in the early morning and evening, although breeding and feeding activities may change this pattern seasonally. Where human food of garbage is available, black bears may become more active at night or during the day, depending on the food source. Cases where black bears become a nuisance are usually associated with human food sources. Black bears are normally shy but will also eat virtually anything, they will knock over garbage cans and break into cars and houses to get at food.

Black bears rest in bed sites in forest habitat; these are usually simple, shallow depressions in the forest leaf litter. Black bears are normally solitary animals except for female groups (adult females and their cubs), breeding pairs in summer, and congregations at feeding sites. In areas where food sources are aggregated, large numbers of bears congregate and form social hierarchies, including non-related animals of the same sex that travel and play together. At other times black bears tend to avoid each other. Territories are established by adult females during the summer. Males establish territories that are large enough to obtain food and overlap with the ranges of several females. They are typically shy and secretive among themselves and towards humans. They rarely become aggressive, unless injured or cornered. Black bears are very intelligent and curious animals, they are excellent problem solvers and are ingenious at finding their way into places where there is food. Black bears have amazing abilities to find their way across large distances. They have been known to return to particular spots as adults that they were shown as cubs by their mother. These navigational abilities are poorly understood.

Black bears can run as fast as 25 miles per hour while they chase prey, and they are skillful tree climbers.

Home Range

How do they communicate with each other?

Black bears communicate with body and facial expressions, sounds, touch, and through scent marking. Scent marks advertise territory boundaries to other bears. Black bears have a keen sense of smell. (Lariviere, 2001)

What do they eat?

Black bears are omnivorous. They eat plants, fruit, insects and their larvae, seeds and nuts, flesh, and carrion. Available food types vary from season to season and between regions. Only a small portion of a bears diet consists of animal matter, and this is usually made up of colonial insects, such as termites, and beetles. Most vertebrate are consumed as carrion. Black bears are not active predators and hunt vertebrates only if the opportunity exists. In spring, after black bears emerge from their winter dens, is a time when food is scarce. Bears tend to lose weight during this period and continue to live off of body fat stored during the previous fall. As summer approaches, black bears begin to eat a wide variety of berry crops and the large numbers of insects that are emerging. In the fall they put on large amounts of fat in preparation for the winter sleep.

  • Plant Foods
  • roots and tubers
  • seeds, grains, and nuts
  • fruit

What eats them and how do they avoid being eaten?

Black bear cubs may be at risk of being killed by large predators, such as wolves and mountain lions. However, most black bears that are killed, both young and adults, are killed by humans. (Lariviere, 2001)

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

Black bears are important in ecosystems because of their effects on populations of insects and fruits. They help to disperse the seeds of the plants they eat and consume large numbers of colonial insects and moth larvae. They sometimes take small and large mammals as prey, such as rabbits and deer. (Lariviere, 2001)

Do they cause problems?

Black bears have been known to occasionally kill livestock. However, attacks on livestock are very rare. Bears can do serious damage to cornfields and honey production. Some bears have become troublesome around camps and cabins if food is left within their reach. Black bears have severely injured and sometimes even killed campers or travelers who feed them. However, the danger associated with black bears is often overstated, fewer than 36 human deaths resulted from black bear encounters in the 20th century. Black bears are generally very timid and, unlike grizzly bear females, black bear mothers with cubs are unlikely to attack people. When black bear mothers confront humans, they send their cubs up a tree and retreat or bluff.

  • Ways that these animals might be a problem for humans
  • injures humans
    • bites or stings
  • crop pest

How do they interact with us?

People have intensively hunted black bears as trophies and for its hide, meat, and fat. In most of the states and provinces occupied by black bears, they are treated as a game animal, which means that regulated hunting is allowed. An estimated 30,000 black bears are killed annually in North America. Relatively few skins go to market now, as regulations sometimes forbid commerce and there is no great demand.

Medical research on the ways that black bears use to survive long period of low activity is giving researchers new insight into treatments for kidney failure, gallstones, severe burns, and other illnesses.

  • Ways that people benefit from these animals:
  • body parts are source of valuable material
  • research and education

Are they endangered?

Black bears once lived throughout most of North America, but hunting and agriculture drove them into heavily forested areas. Populations surive over much of their former range in less populated wooded regions and in protected areas. They are numerous and thriving, although they continue to face threats in some areas due to habitat destruction. Black bears appear in CITES appendix II.

Contributors

Tanya Dewey (author), Animal Diversity Web.

Christine Kronk (author), University of Michigan-Ann Arbor.

References

Academic American Encyclopedia. 1994. Grolier Incorporated. Danbury, CT.

Collier's Encyclopedia. 1993. Collier Incorporated. New York, NY.

Encyclopedia Americana. 1994. Grolier Incorporated. Danbury, CT.

The Carnivores. Ewer, R.F. 1973. Cornell University Press. Ithaca, NY.

Walker's Mammals of the World, 4th Ed. Nowak, Ronald, M. and John L. Paradiso. 1983. Johns Hopkins University Press, Baltimore, MD.

Wild Mammals of North America. Chapman, Joseph, A. and George A. Feldhamer. 1982.Johns Hopkins University Press. Baltimore, MD.

World Book Encyclopedia. 1994. World Book Incorporated. Chicago, IL.

Lariviere, S. 2001. Ursus americanus. Mammalian Species, 647: 1-11. Accessed September 02, 2006 at http://www.science.smith.edu/departments/Biology/VHAYSSEN/msi/default.html.

Northwest Territories: Resources, Wildlife, and Economic Development Division, August 27, 2001. "Encountering Bears" (On-line). Accessed August 28, 2002 at http://www.nwtwildlife.rwed.gov.nt.ca/Publications/safetyinbearcountry/encounters.htm.

 
University of Michigan Museum of ZoologyNational Science Foundation

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Kronk, C. 2007. "Ursus americanus" (On-line), Animal Diversity Web. Accessed October 24, 2014 at http://www.biokids.umich.edu/accounts/Ursus_americanus/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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