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American Black Bear

Ursus americanus

Summary 3

The American black bear (Ursus americanus) is a medium-sized bear native to North America. It is the continent's smallest and most widely distributed bear species. Black bears are omnivores with their diets varying greatly depending on season and location. They typically live in largely forested areas, but do leave forests in search of food. Sometimes they become attracted to human communities because of the immediate availability of food. The American black bear is the world's most...

Description 4

Most Black Bears hibernate for up to seven months, and do not eat, drink, urinate, or exercise the entire time. In the South, where plant food is available all year, not all bears hibernate—but pregnant females do. The female gives birth to 1-6 cubs (usually 2 or 3) in January, while she is deep asleep in her den. The newborn cubs snuggle next to her for warmth and nurse while she fasts. They grow from a birth weight of 200-450 g each (about 7-16 pounds) to the 2-5 kg they will weigh when the family leaves the den in the spring. Black Bears eat a little meat, and some insects, but they rely on fruit, nuts, and vegetation for the bulk of their nutritional needs. They are not all black. Most are, with brown muzzles, but in some western forests they are brown, cinnamon, or blond, and a few, in southern Alaska and British Columbia, are creamy white or bluish-gray.

Adaptation: In the Black Bear, Ursus americanus, the evolution of typically carnivorous, sharp shearing molars into the flat crushing teeth, typical of bears, is evident.

Links:
Mammal Species of the World

Distribution 5

Global Range: (100-250 square km (about 40-100 square miles)) Black bears exist throughout most of North America north of central Mexico, except the desert region of the southwestern United States, from north-central Alaska across boreal Canada to Labrador and Newfoundland, and south to central California, northern Nevada, northern Nayarit and southern Tamaulipas (Mexico), and Florida (Wozencraft, in Wilson and Reeder 1993). However, the species has been eliminated from most of the Midwest by intensive agriculture and human settlement. Now it occurs primarily in remaining large forested tracts.

Habitat 6

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 ; terrestrial

Terrestrial Biomes: forest ; scrub forest

Other Habitat Features: riparian

Habitat and ecology 7

Habitat and Ecology

American black bears are primarily a species of temperate and boreal forests, but they also range into subtropical areas of Florida and Mexico as well as into the subarctic. They live at elevations ranging from sea level to 3,500 m, and inhabit areas as diverse as dry Mexican scrub forests, Louisiana swamps, Alaskan rainforests, and Labrador tundra (where they occupy the typical niche of the brown/grizzly bear [U. arctos]; Veitch and Harrington 1996). Between these extremes they occupy assorted deciduous and coniferous forest types, each providing a different array of foods.

The American black bear is a generalist, opportunist, omnivore. Depending on location and season, they consume herbaceous vegetation, roots, buds, numerous kinds of fleshy fruits, nuts, insects in life stages from egg to adult, and vertebrates from fish to mammals, including their own kills as well as carrion. Moreover, they readily consume various human-related foods, from garbage and birdseed to a variety of agricultural products, including standing corn and oats just before harvest, apples, and honey and brood in apiaries. The ability of black bears to vary their diet with the circumstances has enabled them to persist not only in a diversity of habitat types, but also in highly fragmented forested areas in proximity to humans (Pelton 2003).

A key habitat feature in many areas is a source of fall mast that enables black bears to increase their fat reserves in preparation for winter. Historically, American chestnuts (Castanea dentata) likely were a key fall food in eastern North America, but since a blight eliminated this food source in the early and mid 1900s, oak (Quercus spp.) acorns and beechnuts (Fagus grandifolia) have become the principal fall foods for bears throughout this region (Vaughan 2002). In areas where oaks and beech are absent or uncommon, hazelnuts (Corylus spp.), whitebark pine nuts (Pinus albicaulis), madrone (Arbutus xalapensis), mansanita (Arctostaphylos spp.), huckleberries (Vaccinium spp.), buffalo berries (Shepherdia canadensis) or other fruits, or sometimes meat, are the fall dietary mainstays. In the southwestern U.S. and in Mexico, succulents such as yucca (Yucca spp.) and cacti also play important roles in providing food, especially during drought (Doan-Crider 2003).

American black bears hibernate for up to 7 months in the northern portions of their range, but considerably shorter in more southern areas. In some southern areas, where food is available year-round, they may remain active during winter. However, all parturient females den and give birth to cubs, typically in January–February. Although mating occurs in May–July, implantation is delayed and active gestation is only 2 months. Females give birth beginning at age 3–8 years, depending on food availability and hence their body weight, and can produce cubs every other year (in places with less food, this interval is often extended to 3 years). Average litter size is approximately 2.5 cubs in eastern and 2.0 cubs in western North America (Alt 1989).

Systems
  • Terrestrial

I dnature guides 8

Identification key for mammals of North America

Known predators 9

Ursus americanus is prey of:
Homo sapiens
Canis lupus
Puma concolor

This list may not be complete but is based on published studies.

Known prey organisms 10

Ursus americanus preys on:
Microtus xanthognathus
Cervus elaphus
Rangifer tarandus
Alces alces

This list may not be complete but is based on published studies.

Life expectancy 11

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.

Range lifespan
Status: wild: 30.0 (high) years.

Average lifespan
Status: wild: 10.0 years.

Average lifespan
Sex: female
Status: wild: 26.0 years.

Average lifespan
Status: wild: 32.0 years.

Migration 12

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Black bears exhibit large variations in home range, depending on location and gender(Banfield 1974, Baker 1983, Klenner 1987). Female and subadult ranges typically are much smaller than those of adult males. In Minnesota, females rarely dispersed from natal home range, males dispersed when 2-4 years old (Rogers 1987). In western North Carolina, neighboring individuals often used areas of overlap for same activities and at same time (Horner and Powell 1990). Home ranges of males averaged 505 hectares on Long Island, Washington (Lindzey and Meslow 1977), 5,200 hectares in northern Washington (Poelker and Hartwell 1973), 1,060 hectares in northwestern California (Kelleyhouse 1975) and 2,240 hectares in the San Bernardino Mountains of southern California (Novick 1979). Home ranges in Idaho ranged from 1,660 to 13,030 hectares (Armstrup and Beecham 1976).

Morphology 13

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.

Range mass: 39.0 to 409.0 kg.

Range length: 1200.0 to 2000.0 mm.

Other Physical Features: endothermic ; heterothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Range description 14

American black bears are found through much of Canada, the United States, and the northern half of Mexico. Although they were extirpated from large portions of their historic range because of habitat loss and (mainly intentional) overexploitation, their occupied range has been expanding in recent years (Pelton et al. 1999, Williamson 2002). The species has, nevertheless been extirpated from large parts of its former range, especially in the Midwest of the United States, and in Mexico. American black bears presently occupy all provinces and territories of Canada, except Prince Edward Island (where they were extirpated in 1937), 41 U.S. states (with occasional sightings in at least 3 others), and 8 states of northern Mexico. The species never existed outside of these three countries.

Reproduction 15

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

Mating System: 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.

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 gestation period: 220.0 days.

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.

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

Average birth mass: 277.5 g.

Average gestation period: 70 days.

Average number of offspring: 2.

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 ; 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

Size in north america 16

Sexual Dimorphism: The largest males may be nearly twice as heavy as the heaviest females.

Length:
Range: 1,44-2,000 mm males; 1,200-1,600 mm females

Weight:
Average: 120 kg males; 80 kg females
Range: 47-409 kg males; 39-236 kg females

Taxonomy 17

Comments: Characterized by a relatively low level of protein variation (see Cronin et al. 1991). Cronin et al. (1991) found very similar mtDNA haplotypes among black bears from Alaska, Montana, Oregon, and New Hampshire, though divergent haplotypes were identified in the populations from Montana and Oregon; evidently there has been maintenance of polymorphism and considerable gene flow throughout the history of the species. Bears from insular Newfoundland, New Brunswick, and Quebec, and most individuals from Alberta, exhibited very closely related mtDNA haplotypes; Newfoundland bears apparently arose through rapid genetic drift associated with a founder effect during postglacial colonization (Paetkau and Strobeck 1996).

Bears from Haida Gwaii (Queen Charlotte Islands), Vancouver Island, and coastal mainland British Columbia are indistinguishable with respect to mtDNA, but these bears are highly distinct from inland continental bears; the coastal mtDNA lineage occurs in each of the three recognized coastal subspecies, suggesting that the morphological characteristics differentiating these taxa may be postglacially derived (Byun et al. 1997).

See Cronin et al. (1991) and Shields and Kocher (1991) for information on phylogenetic relationships of North American ursids based on an analysis of mitochondrial DNA (black bear has been separated from brown and polar bears much longer than brown and polar bears have been separated from each other).

Threats 18

Degree of Threat: D : Unthreatened throughout its range, communities may be threatened in minor portions of the range or degree of variation falls within natural variation

Comments: Locally threatened by habitat loss and interference by humans. Black market value of gall bladder and paws has led to an increase in the illegal harvest of this species.

Trophic strategy 19

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.

Animal Foods: carrion ; insects

Plant Foods: roots and tubers; seeds, grains, and nuts; fruit

Primary Diet: omnivore

Associations 20

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.

Behaviour 21

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 ; tactile ; acoustic ; chemical

Perception Channels: visual ; tactile ; acoustic ; chemical

Conservation status 22

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.

US Federal List: no special status

CITES: appendix ii

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Sources and Credits

  1. (c) Kim Cabrera, some rights reserved (CC BY-NC-ND), uploaded by Kim Cabrera
  2. (c) Arthur Chapman, some rights reserved (CC BY-NC-SA), http://farm3.static.flickr.com/2669/3996977252_499c42d5b9.jpg
  3. Adapted by Kim Cabrera from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Ursus_americanus
  4. (c) Smithsonian Institution, some rights reserved (CC BY), http://eol.org/data_objects/6625857
  5. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28834447
  6. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429038
  7. (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31299396
  8. (c) Discover Life and original sources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/11585699
  9. (c) SPIRE project, some rights reserved (CC BY), http://eol.org/data_objects/10543622
  10. (c) SPIRE project, some rights reserved (CC BY), http://eol.org/data_objects/10543621
  11. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429041
  12. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28834456
  13. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429039
  14. (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31299394
  15. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429040
  16. (c) Smithsonian Institution, some rights reserved (CC BY), http://eol.org/data_objects/6625858
  17. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28834439
  18. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28834444
  19. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429043
  20. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429045
  21. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429042
  22. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31429048

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