Ursus americanusAmerican black bear

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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). (Lariviere, 2001)

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. (Lariviere, 2001)

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. (Lariviere, 2001)

  • 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

Reproduction

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

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. (Lariviere, 2001)

  • Breeding interval
    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

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. (Lariviere, 2001)

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. (Lariviere, 2001)

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. (Lariviere, 2001)

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. (Lariviere, 2001)

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. (Lariviere, 2001)

  • 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. (Lariviere, 2001)

  • Anti-predator Adaptations
  • 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. (Lariviere, 2001)

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. (Lariviere, 2001)

  • 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. (Lariviere, 2001; Northwest Territories: Resources, Wildlife, and Economic Development Division, August 27, 2001)

  • 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. (Lariviere, 2001)

Contributors

Tanya Dewey (author), Animal Diversity Web.

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

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

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.