Ursus americanus

Geographic Range

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 U.S. into central Mexico (Nayarit and Tamaulipas states).

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Throughout their range, prime black bear habitat is characterized by relatively inaccessible terrain, thick understory vegetation, and abundant sources of food in the form of shrub or tree-borne soft or hard mast. In the southwest, prime black bear habitat is restricted to vegetated, mountainous areas ranging from 900 to 3,000 m in elevation. Habitats consist mostly of chaparral and pinyon-juniper woodland sites. Bears occasionally move out of the chaparral into more open sites and feed on prickly pear cactus. There are at least two distinct, prime habitat types in the Southeast. Black bears in the southern Appalachian Mountains survive in a predominantly oak- hickory and mixed mesophytic forest. In the coastal areas of the southeast, bears inhabit a mixture of flatwoods, bays, and swampy hardwood sites. In the northeast, prime habitat consists of a forest canopy of hardwoods such as beech, maple, and birch, and coniferous species. Swampy habitat areas are mainly white cedar. Corn crops and oak-hickory mast are also common sources of food in some sections of the northeast; small, thick swampy areas provide excellent refuge cover. Along the Pacific coast, redwood, sitka spruce, and hemlocks predominate as overstory cover. Within these forest types are early successional areas important for black bears, such as brushfields, wet and dry meadows, high tidelands, riparian areas and a variety of mast-producing hardwood species. The spruce-fir forest dominates much of the range of the black bear in the Rockies. Important nonforested areas are wet meadows, riparian areas, avalanche chutes, roadsites, burns, sidehill parks, and subalpine ridgetops.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• scrub forest scrub forest

• Other Habitat Features
• riparian riparian

Physical Description

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. The distance between the canine teeth is about 4.5 to 5 cm.

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.

• Other Physical Features
• endothermic endothermic
• heterothermic heterothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

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

• Mating System
• polygynous polygynous

The sexes coexist briefly during the mating season, which generally peaks from June to mid-July. Females remain in estrus throughout the season until they mate. They usually give birth every other year, but sometimes wait 3 or 4 years. Pregnancy generally lasts about 220 days, but this includes a delayed implantation. The fertilized eggs are not implanted in the uterus until the autumn, and embryonic development occurs only in the last 10 weeks of pregnancy. Births occur mainly in January and February, commonly 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. Black bear cubs remain in the den with their torpid 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 female is coming into estrus and forces the young out of her territory. They may weigh between 7 and 49 kg at this point, depending on food supplies.

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous
• delayed implantation delayed implantation

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.

• Parental Investment
• altricial 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

Lifespan/Longevity

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.

Behavior

Black bears are generally crepuscular, although breeding and feeding activities may alter this pattern seasonally. Where human food of garbage is available, individuals may become distinctly diurnal (on roadsides) or nocturnal (in campgrounds). Nuisance activities are usually associated with sources of artificial food and the very opportunistic feeding behaviors of black bears. During periods of inactivity, black bears utilize bed sites in forest habitat; these sites generally consist of a simple shallow depression in the forest leaf litter. Black bears are normally solitary animals except for female groups (adult female and 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.

The highly evolved family behavioral relationships probably are the result of the slow maturation of cubs and the high degree of learning associated with obtaining food and navigating through large territories. Black bears possess a high level of intelligence and exhibit a high degree of curiosity and exploratory behaviors. Although black bears are generally characterized as shy and secretive animals toward humans, they exhibit a much wider array of intraspecific and interspecific behaviors than originally thought. Black bears have extraordinary navigational abilities which are poorly understood.

• Key Behaviors
• terricolous
• crepuscular crepuscular
• motile motile
• nomadic nomadic
• sedentary sedentary
• hibernation hibernation
• solitary solitary
• territorial territorial

Home Range

Territories are established by adult females during the summer. Temporal spacing is exhibited by individuals at other times of the year and is likely maintained through a dominance hierarchy system. Males establish territories that are large enough to obtain food and overlap with the ranges of several females.

Communication and Perception

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.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Throughout their range in North America, black bears consume primarily grasses and forbs in spring, soft mast in the form of shrub and tree-borne fruits in summer, and a mixture of hard and soft mast in fall. However, the availability of different food types varies regionally. Only a small portion of the diet of bears consists of animal matter, and then primarily in the form of colonial insects and beetles. Most vertebrates are consumed in the form of carrion. Black bears are not active predators and feed on vertebrates only if the opportunity exists.

The diet of black bears is high in carbohydrates and low in proteins and fats. Consequently, they generally prefer foods with high protein or fat content, thus their propensity for the food and garbage of people. Bears feeding on a protein-rich food source show significant weight gains and enhanced fecundity. Spring, after black bears emerge from winter dens, is a period of relative food scarcity. Bears tend to lose weight during this period and continue to subsist partly off of body fat stored during the preceding fall. They take advantage of any succulent and protein- rich foods available; however, these are not typically in sufficient quantity to maintain body weight. As summer approaches, a variety of berry crops become available. Summer is generally a period of abundant and diverse foods for black bears, enabling them to recover from the energy deficits of winter and spring. Black bears accumulate large fat reserves during the fall, primarily from fruits, nuts, and acorns.

• Primary Diet
• omnivore omnivore

• Animal Foods
• carrion carrion
• insects

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

Predation

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.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

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.

Economic Importance for Humans: Positive

People have intensively hunted U. americanus , for trophy value and for various products, including hides for clothes or rugs, and meat and fat for food. In most of the states and provinces occupied by black bears, they are treated as game animals, subject to regulated hunting. An estimated 30,000 individuals 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 metabolic pathways that black bears use to survive long period of torpor is yielding new insight into treatments for kidney failure, gallstones, severe burns, and other illnesses.

• Positive Impacts
• body parts are source of valuable material
• research and education

Economic Importance for Humans: Negative

Black bears have been known to occasionally raid livestock, though losses to bears are negligible. Bears sometimes damage cornfields, and berry and honey production. Some bears have become troublesome around camps and cabins if food is left in 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 sometimes 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 typically send their cubs up a tree and retreat or bluff. People who live in or visit areas with black bears should be aware of the appropriate precautions for avoiding black bear encounters.

• Negative Impacts
• injures humans
  • bites or stings
• crop pest

Conservation Status

Black bears once lived throughout most of North America, but hunting and agriculture drove them into heavily forested areas. Residual populations survive over much of the range in sparsely populated wooded regions and under protection in national parks. They are numerous and thriving, but continue to face threats regionally due to habitat destruction and hunting. Black bears appear in CITES appendix II.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Tanya Dewey (author), Animal Diversity Web.

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

References

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 .

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.