GALLERIES > MAMMALS > AMERICAN BLACK BEAR [Ursus americanus]
Location: Yellowstone National Park, WyomingGPS: 44.3N, -110.6W, elev=8,038' MAP
Date: July 25, 2019
ID : B13K8520 [4896 x 3264]
Location: Yellowstone National Park, WyomingGPS: 44.3N, -110.6W, elev=8,038' MAP
Date: July 25, 2019
ID : B13K8504 [4896 x 3264]
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. American 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 common bear species.
It is listed by the International Union for Conservation of Nature (IUCN) as a least-concern species, due to its widespread distribution and a large population estimated to be twice that of all other bear species combined. Along with the brown bear, it is one of only two of the eight modern bear species not considered by the IUCN to be globally threatened with extinction. American black bears often mark trees using their teeth and claws as a form of communication with other bears, a behavior common to many species of bears.
Despite living in North America, American black bears are not closely related to brown bears and polar bears; genetic studies reveal that they split from a common ancestor 5.05 million years ago (mya). American and Asian black bears are considered sister taxa and are more closely related to each other than to the other modern species of bears. According to recent studies, the sun bear is also a relatively recent split from this lineage.
A small primitive bear called Ursus abstrusus is the oldest known North American fossil member of the genus Ursus, dated to 4.95 mya. This suggests that U. abstrusus may be the direct ancestor of the American black bear, which evolved in North America. Although Wolverton and Lyman still consider U. vitabilis an "apparent precursor to modern black bears", it has also been placed within U. americanus.
The ancestors of American black bears and Asian black bears diverged from sun bears 4.58 mya. The American black bear then split from the Asian black bear 4.08 mya. The earliest American black bear fossils, which were located in Port Kennedy, Pennsylvania, greatly resemble the Asian species, though later specimens grew to sizes comparable to grizzly bears. From the Holocene to the present, American black bears seem to have shrunk in size, but this has been disputed because of problems with dating these fossil specimens.
The American black bear lived during the same period as the giant and lesser short-faced bears (Arctodus simus and A. pristinus, respectively) and the Florida spectacled bear (Tremarctos floridanus). These tremarctine bears evolved from bears that had emigrated from Asia to North America 78 ma. The giant and lesser short-faced bears are thought to have been heavily carnivorous and the Florida spectacled bear more herbivorous, while the American black bears remained arboreal omnivores, like their Asian ancestors. The American black bear's generalist behavior allowed it to exploit a wider variety of foods and has been given as a reason why, of these three genera, it alone survived climate and vegetative changes through the last Ice Age while the other, more specialized North American predators became extinct. However, both Arctodus and Tremarctos had survived several other, previous ice ages. After these prehistoric ursids became extinct during the last glacial period 10,000 years ago, American black bears were probably the only bear present in much of North America until the migration of brown bears to the rest of the continent.
American black bears are reproductively compatible with several other bear species and have occasionally produced hybrid offspring. According to Jack Hanna's Monkeys on the Interstate, a bear captured in Sanford, Florida, was thought to have been the offspring of an escaped female Asian black bear and a male American black bear. In 1859, an American black bear and a Eurasian brown bear were bred together in the London Zoological Gardens, but the three cubs that were born died before they reached maturity. In The Variation of Animals and Plants under Domestication, Charles Darwin noted:
In the nine-year Report it is stated that the bears had been seen in the zoological gardens to couple freely, but previously to 1848 most had rarely conceived. In the reports published since this date three species have produced young (hybrids in one case), ...
An American black bear shot in autumn 1986 in Michigan was thought by some to be an American black bear/grizzly bear hybrid, due to its unusually large size and its proportionately larger braincase and skull. DNA testing was unable to determine whether it was a large American black bear or a grizzly bear.
Historically, American black bears occupied the majority of North America's forested regions. Today, they are primarily limited to sparsely settled, forested areas. American black bears currently inhabit much of their original Canadian range, though they seldom occur in the southern farmlands of Alberta, Saskatchewan and Manitoba; they have been extinct on Prince Edward Island since 1937. The total Canadian black bear population is between 396,000 and 476,000, based on surveys taken in the mid-1990s in seven Canadian provinces, though this estimate excludes American black bear populations in New Brunswick, the Northwest Territories, Nova Scotia and Saskatchewan. All provinces indicated stable populations of American black bears over the last decade.
The current range of American black bears in the United States is constant throughout most of the northeast and within the Appalachian Mountains almost continuously from Maine to northern Georgia, the northern Midwest, the Rocky Mountain region, the West Coast and Alaska. However, it becomes increasingly fragmented or absent in other regions. Despite this, American black bears in those areas seem to have expanded their range during the last decade, such as with recent sightings in Ohio and southern Indiana, though these probably do not yet represent stable breeding populations. Sightings of itinerant American black bears in the Driftless Area of southeast Minnesota, northeast Iowa, and southwest Wisconsin are common. In the spring of 2019, biologists with the Iowa Department of Natural Resources confirmed documentation of an American black bear living year-round in woodlands near the town of Decorah in northeast Iowa, believed to be the first instance of a resident black bear in Iowa since the 1880s.
Surveys taken from 35 states in the early 1990s indicate that American black bears are either stable or increasing, except in Idaho and New Mexico. The overall population of American black bears in the United States has been estimated to range between 339,000 and 465,000, though this excludes populations from Alaska, Idaho, South Dakota, Texas and Wyoming, whose population sizes are unknown. In the state of California, there are an estimated 25,000-35,000 American black bears, making it the largest population of the species in the contiguous United States.
As of 1993, known Mexican black bear populations existed in four areas, though knowledge on the distribution of populations outside those areas has not been updated since 1959. Mexico is the only country where the American black bear is classified as "endangered".
There have been several sightings quite far away from where the American black bear is normally found, such as Union County, North Carolina and western Nebraska.
Throughout their range, habitats preferred by American black bears have a few shared characteristics. They are often found in areas with relatively inaccessible terrain, thick understory vegetation and large quantities of edible material (especially masts). The adaptation to woodlands and thick vegetation in this species may have originally been due to the American black bear having evolved alongside larger, more aggressive bear species, such as the extinct giant short-faced bear and the still-living grizzly bear, that monopolized more open habitats and the historic presence of larger predators, such as Smilodon and the American lion, that could have preyed on American black bears. Although found in the largest numbers in wild, undisturbed areas and rural regions, American black bears can adapt to surviving in some numbers in peri-urban regions, as long as they contain easily accessible foods and some vegetative coverage.
In most of the contiguous United States, American black bears today are usually found in heavily vegetated mountainous areas, from 400 to 3,000 m (1,300 to 9,800 ft) in elevation. For American black bears living in the American Southwest and Mexico, habitat usually consists of stands of chaparral and pinyon juniper woods. In this region, bears occasionally move to more open areas to feed on prickly pear cactus. At least two distinct, prime habitat types are inhabited in the Southeastern United States. American black bears in the southern Appalachian Mountains survive in predominantly oak-hickory and mixed mesophytic forests. In the coastal areas of the Southeast (such as Florida, the Carolinas and Louisiana), bears inhabit a mixture of flatwoods, bays and swampy hardwood sites.
In the northeast part of the range (United States and Canada), prime habitat consists of a forest canopy of hardwoods such as beech, maple, birch and coniferous species. 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 largely in stands of white cedar. Along the Pacific coast, redwood, Sitka spruce and hemlocks predominate as overstory cover. Within these northern forest types are early successional areas important for American black bears, such as fields of brush, 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 American black bear in the Rockies. Important nonforested areas here are wet meadows, riparian areas, avalanche chutes, roadsides, burns, sidehill parks and subalpine ridgetops.
In areas where human development is relatively low, such as stretches of Canada and Alaska, American black bears tend to be found more regularly in lowland regions. In parts of northeastern Canada, especially Labrador, American black bears have adapted exclusively to semi-open areas that are more typical habitat in North America for brown bears (likely due to the absence here of brown and polar bears, as well as other large carnivore species).
The skulls of American black bears are broad, with narrow muzzles and large jaw hinges. In Virginia, the total length of adult bear skulls was found to average 262 to 317 mm (10.3 to 12.5 in). Across its range, the greatest skull length for the species has been reportedly measured from 23.5 to 35 cm (9.3 to 13.8 in). Females tend to have slenderer and more pointed faces than males. Their claws are typically black or grayish-brown. The claws are short and rounded, being thick at the base and tapering to a point. Claws from both hind and front legs are almost identical in length, though the foreclaws tend to be more sharply curved. The paws of the species are relatively large, with a rear foot length of 13.7 to 22.5 cm (5.4 to 8.9 in), which is proportionately larger than other medium-sized bear species, but much smaller than the paws of large adult brown, and especially polar, bears. The soles of the feet are black or brownish and are naked, leathery and deeply wrinkled. The hind legs are relatively longer than those of Asian black bears. The vestigial tail is usually 4.8 inches (120 mm) long. The ears are small and rounded and are set well back on the head.
American black bears are highly dexterous, being capable of opening screw-top jars and manipulating door latches. They also have great physical strength. They have been known to turn over flat-shaped rocks weighing 310 to 325 pounds (141 to 147 kg) by flipping them over with a single foreleg. They move in a rhythmic, sure-footed way and can run at speeds of 25 to 30 miles per hour (40 to 48 km/h). American black bears have good eyesight and have been proven experimentally to be able to learn visual color discrimination tasks faster than chimpanzees and just as fast as domestic dogs. They are also capable of rapidly learning to distinguish different shapes such as small triangles, circles and squares.
Cinnamon-colored American black bear in Yellowstone National Park
American black bear weight tends to vary according to age, sex, health and season. Seasonal variation in weight is very pronounced: in autumn, their pre-den weight tends to be 30% higher than in spring, when black bears emerge from their dens. American black bears on the East Coast tend to be heavier on average than those on the West Coast, although American black bears follow Bergmann's rule and bears from the Northwest are often slightly heavier than the bears from the Southeast. Adult males typically weigh between 57250 kg (126551 lb), while females weigh 33% less at 41170 kg (90375 lb).
In the state of California, studies have indicated that the average mass is 86 kg (190 lb) in adult males and 58 kg (128 lb) in adult females. Adult American black bears in Yukon Flats National Wildlife Refuge in east-central Alaska were found to average 87.3 kg (192 lb) in males and 63.4 kg (140 lb) in females, whereas on Kuiu Island in southeast Alaska (where nutritious salmon are readily available) adult American black bears averaged an estimated 115 kg (254 lb). In Great Smoky Mountains National Park, adult males averaged 112 kg (247 lb) and adult females averaged 47 kg (104 lb) per one study. In one of the largest studies on regional body mass, bears in British Columbia averaged 73.7 kg (162 lb) in 89 females and 103.1 kg (227 lb) in 243 males. In Yellowstone National Park, a population study found that adult males averaged 119 kg (262 lb) and adult females averaged 67 kg (148 lb). Black bears in north-central Minnesota averaged 69.9 kg (154 lb) in 163 females and 124.95 kg (275 lb) in 77 males. In New York, the two sexes reportedly average 135 kg (298 lb) and 74 kg (163 lb), respectively. It was found in Nevada and Lake Tahoe region that black bears closer to urban regions were significantly heavier than their arid-country dwelling counterparts, with males near urban areas averaging 138 kg (304 lb) against wild-land males which averaged 115.5 kg (255 lb) whereas peri-urban females averaged 97.9 kg (216 lb) against the average of 65.2 kg (144 lb) in wild-land ones. In Waterton Lakes National Park, Alberta adults reportedly averaged 125 to 128 kg (276 to 282 lb). Adults typically range from 120 to 200 cm (47 to 79 in) in head-and-body length, and 70 to 105 cm (28 to 41 in) in shoulder height. The typically small tail is 7.717.7 cm (3.07.0 in) long. Although they are the smallest bear species in North America, large males exceed the size of other bear species, except the brown bear and the polar bear.
The biggest wild American black bear ever recorded was a male from New Brunswick, shot in November 1972, that weighed 409 kg (902 lb) after it had been dressed, meaning it weighed an estimated 500 kg (1,100 lb) in life and measured 2.41 m (7.9 ft) long. Another notably outsized wild American black bear, weighing in at 408 kg (899 lb) in total, was the cattle-killer shot in December 1921 on the Moqui Reservation in Arizona. The record-sized American black bear from New Jersey was shot in Morris County December 2011 and scaled 376.5 kg (830 lb). Even larger, the most massive American black bear recorded in Pennsylvania (one of six weighing over 363 kg (800 lb) shot in the last 15 years in the state) weighed in at 399 kg (880 lb) and was shot in November 2010 in Pike County. The North American Bear Center, located in Ely, Minnesota, is home to the world's largest captive male and female American black bears. Ted, the male, weighed 431453.5 kg (9501,000 lb) in the fall of 2006. Honey, the female, weighed 219.6 kg (484 lb) in the fall of 2007.
The fur is soft, with dense underfur and long, coarse, thick guard hairs. The fur is not as shaggy or coarse as that of brown bears. American black bear skins can be distinguished from those of Asian black bears by the lack of a white blaze on the chest and hairier footpads. Despite their name, American black bears show a great deal of color variation. Individual coat colors can range from white, blonde, cinnamon, light brown or dark chocolate brown to jet black, with many intermediate variations existing. Silvery-gray American black bears with a blue luster (this is found mostly on the flanks) occur along a portion of coastal Alaska and British Columbia. White to cream-colored American black bears occur in the coastal islands and the adjacent mainland of southwestern British Columbia. Albino specimens have also been recorded. Black coats tend to predominate in moist areas such as Maine, New York, Tennessee, Michigan and western Washington. Approximately 70% of all American black bears are black, though only 50% of American black bears in the Rocky Mountains are black. Many American black bears in northwestern North America are cinnamon, blonde or light brown in color and thus may sometimes be mistaken for grizzly bears. Grizzly (and other types of brown) bears can be distinguished by their shoulder hump, larger size and broader, more concave skull.
In his book The Great Bear Almanac, Gary Brown summarized the predominance of black or brown/blonde specimens by location:
An American black bear has better eyesight and a better sense of hearing compared to humans. Their keenest sense is their sense of smell, which is about seven times greater than a domestic dog's. American black bears are excellent and strong swimmers, doing so for pleasure and to feed (largely on fish). They regularly climb trees to feed, escape enemies and hibernate. Four of the eight modern bear species are habitually arboreal (the most arboreal species, the American and Asian black bears and the sun bear, being fairly closely related). Their arboreal abilities tend to decline with age. American black bears may be active at any time of the day or night, although they mainly forage by night. American black bears living near human habitations tend to be more extensively nocturnal and American black bears living near brown bears tend to be more extensively diurnal. Their social behavior is somewhat similar to that of canids.
American black bears tend to be territorial and non-gregarious in nature. However, at abundant food sources (i.e. spawning salmon or garbage dumps), American black bears may congregate and dominance hierarchies form, with the largest, most powerful males dominating the most fruitful feeding spots. They mark their territories by rubbing their bodies against trees and clawing at the bark. Annual ranges held by mature male American black bears tend to be very large, but there is some variation. On Long Island off the coast of Washington, ranges average 5 sq mi (13 km2), whereas on the Ungava Peninsula in Canada ranges can average up to 1,000 sq mi (2,600 km2), with some male bears traveling as far as 4,349 sq mi (11,260 km2) in times of food shortages.
American black bears may communicate with various vocal and non-vocal sounds. Tongue-clicking and grunting are the most common sounds and are made in cordial situations to conspecifics, offspring and occasionally humans. During times of fear or nervousness, bears may moan, huff or blow air. Warning sounds include jaw-clicking and lip-popping. In aggressive interactions, American black bears produce deep-throated pulsing sounds. Cubs may squeal, bawl or scream when in distress and make motor-like humming when comfortable or nursing.
Reproduction and development
Sows usually produce their first litter at the age of three to five years, with those living in more developed areas tending to get pregnant at younger ages. The breeding period usually occurs in the JuneJuly period, though it can extend to August in the species' northern range. The breeding period lasts for two to three months. Both sexes are promiscuous. Males try to mate with several females, but large, dominant ones may violently claim a female if another mature male comes near. Sows tend to be short-tempered with their mates after copulating. The fertilized eggs undergo delayed development and do not implant in the female's womb until November. The gestation period lasts 235 days and litters are usually born in late January to early February. Litter size is between one and six cubs, typically two or three. At birth, cubs weigh 280450 g (0.620.99 lb) and measure 20.5 cm (8.1 in) in length. They are born with fine, gray, down-like hair and their hind quarters are underdeveloped. They typically open their eyes after 2840 days and begin walking after five weeks. Cubs are dependent on their mother's milk for 30 weeks and will reach independence at 1618 months. At the age of six weeks, they attain 900 g (2.0 lb), by the age of eight weeks they reach 2.5 kg (5.5 lb) and by the age of six months they weigh 18 to 27 kg (40 to 60 lb). They reach sexual maturity at the age of three years and attain their full growth at the age of five years.
The average lifespan in the wild is 18 years, though it is quite possible for wild specimens to survive for more than 23 years. The record age of a wild specimen was 39 years, while that in captivity was 44 years. The average annual survival rate for adult American black bears is variable, ranging from 86% in Florida to 73% in Virginia and North Carolina. In Minnesota, 99% of wintering adult bears were able to survive the hibernation cycle in one study. Remarkably, a study of American black bears in Nevada found that the amount of annual mortality of a population of bears in wilderness areas was 0%, whereas in developed areas in the state this figure rose to 83%. Survival in subadults is generally less assured. In Alaska, only 1417% of subadult males and 3048% of subadult females were found in a study to survive to adulthood. Across the range, the estimated number of cubs who survive past their first year is 60%.
With the exception of the rare confrontation with an adult brown bear or a gray wolf pack, adult American black bears are not usually subject to natural predation. However, as evidenced by scats with fur inside of them and the recently discovered carcass of an adult sow with puncture marks in the skull, American black bears may occasionally have fallen, and still do fall, prey to jaguars in the southern parts of their range. In such scenarios, the big cat would have the advantage if it ambushed the bear, killing it with a crushing bite to the back of the skull. American black bear cubs tend to be more vulnerable to predation than adults. Known predators of bear cubs have included bobcats, coyotes, cougars, gray wolves, brown bears and other bears of their own species. Many of these will stealthily snatch small cubs right from under the sleeping mother. There is a single record of a golden eagle snatching a yearling cub. Once out of hibernation, mother bears may be able to fight off most potential predators. Even cougars will be displaced by an angry mother bear if they are discovered stalking the cubs. Flooding of dens after birth may also occasionally kill newborn cubs. However, in current times, American black bear fatalities are overwhelmingly attributable to human activities. Seasonally, tens of thousands of American black bears are hunted legally across North America, with many more being illegally poached or trapped. Auto collisions also may claim many American black bear lives annually.
American black bears were once not considered true or "deep" hibernators, but because of discoveries about the metabolic changes that allow American black bears to remain dormant for months without eating, drinking, urinating or defecating, most biologists have redefined mammalian hibernation as "specialized, seasonal reduction in metabolism concurrent with scarce food and cold weather". American black bears are now considered highly efficient hibernators. The physiology of American black bears in the wild is closely related to that of bears in captivity. Understanding the physiology of bears in the wild is vital to the bear's success in captivity.
The bears enter their dens in October and November, although in the southernmost areas of their range (i.e. Florida, Mexico, the Southeastern United States), only pregnant females and mothers with yearling cubs will enter hibernation. Prior to that time, they can put on up to 14 kg (30 lb) of body fat to get them through the several months during which they fast. Hibernation in American black bears typically lasts 38 months, depending on regional climate.
Hibernating American black bears spend their time in hollowed-out dens in tree cavities, under logs or rocks, in banks, caves, or culverts and in shallow depressions. Although naturally-made dens are occasionally used, most dens are dug out by the bear itself. Females have been shown to be pickier in their choice of dens in comparison to males.
During their time in hibernation, an American black bear's heart rate drops from 4050 beats per minute to 8 beats per minute and the metabolic rate can drop to a quarter of the bear's (non-hibernating) basal metabolic rate (BMR). These reductions in metabolic rate and heart rate do not appear to decrease the bear's ability to heal injuries during hibernation.
The hibernating American black bear does not display the same rate of muscle and bone atrophy relative to other nonhibernatory animals that are subject to long periods of inactivity due to ailment or old age. A hibernating American black bear loses approximately half the muscular strength compared to that of a well-nourished, inactive human. The bear's bone mass does not change in geometry or mineral composition during hibernation, which implies that the bear's conservation of bone mass during hibernation is due to a biological mechanism. During hibernation American black bears retain all excretory waste, leading to the development of a hardened mass of fecal material in the colon known as a fecal plug. A special hormone, leptin, is released into the bear's systems to suppress appetite. The retention of waste during hibernation (specifically in minerals such as calcium) may play a role in the bear's resistance to atrophy.
The body temperature of the American black bear does not drop significantly, like other mammalian hibernators (staying around 35 °C (95 °F)) and they remain somewhat alert and active. If the winter is mild enough, they may wake up and forage for food. Females also give birth in February and nurture their cubs until the snow melts. During winter, American black bears consume 2540% of their body weight. The footpads peel off while they sleep, making room for new tissue.
Many of the physiological changes an American black bear exhibits during hibernation are retained slightly post-hibernation. Upon exiting hibernation, bears retain a reduced heart rate and basal metabolic rate. The metabolic rate of a hibernating bear will remain at a reduced level for up to 21 days after hibernation. After emerging from their winter dens in spring, they wander their home ranges for two weeks so that their metabolism accustoms itself to the activity. In mountainous areas, they seek southerly slopes at lower elevations for forage and move to northerly and easterly slopes at higher elevations as summer progresses.
Generally, American black bears are largely crepuscular in foraging activity, though they may actively feed at any time. Up to 85% of the American black bear's diet consists of vegetation, though they tend to dig less than brown bears, eating far fewer roots, bulbs, corms and tubers than the latter species. When initially emerging from hibernation, they will seek to feed on carrion from winter-killed animals and newborn ungulates. As the spring temperature warms, American black bears seek new shoots of many plant species, especially new grasses, wetland plants and forbs. Young shoots and buds from trees and shrubs during the spring period are also especially important to American black bears emerging from hibernation, as they assist in rebuilding muscle and strengthening the skeleton and are often the only digestible foods available at that time. During summer, the diet largely comprises fruits, especially berries and soft masts such as buds and drupes. During the autumn hyperphagia, feeding becomes virtually the full-time task of American black bears. Hard masts become the most important part of the American black bear's diet in autumn and may even partially dictate the species' distribution. Favored masts such as hazelnuts, oak acorns and whitebark pine nuts may be consumed by the hundreds each day by a single American black bear during the fall. During the fall period, American black bears may also habitually raid the nut caches of tree squirrels. Also extremely important in fall are berries such as huckleberries and buffalo berries. American black bears living in areas near human settlements or around a considerable influx of recreational human activity often come to rely on foods inadvertently provided by humans, especially during summertime. These include refuse, birdseed, agricultural products and honey from apiaries.
The majority of the American black bear's animal diet consists of insects, such as bees, yellow jackets, ants and their larvae. American black bears are also fond of honey and will gnaw through trees if hives are too deeply set into the trunks for them to reach them with their paws. Once the hive is breached, the bears will scrape the honeycombs together with their paws and eat them, regardless of stings from the bees. American black bears that live in northern coastal regions (especially the Pacific Coast) will fish for salmon during the night, as their black fur is easily spotted by salmon in the daytime. However, the white-furred American black bears of the islands of western Canada have a 30% greater success rate in catching salmon than their black-furred counterparts. Other fish, including suckers, trout and catfish, are readily caught whenever possible. Although American black bears do not often engage in active predation of other large animals for much of the year, the species will regularly prey on mule and white-tailed deer fawns in spring, given the opportunity. Bears may catch the scent of hiding fawns when foraging for something else and then sniff them out and pounce on them. As the fawns reach 10 days of age, they can outmaneuver the bears and their scent is soon ignored until the next year. American black bears have also been recorded similarly preying on elk calves in Idaho and moose calves in Alaska.
American black bear predation on adult deer is rare, but it has been recorded. They may even hunt prey up to the size of adult female moose, which are considerably larger than themselves, by ambushing them. There is at least one record of a male American black bear killing two bull elk over the course of six days by chasing them into deep snow banks, which impeded their movements. In Labrador, American black bears are exceptionally carnivorous, living largely off caribou, usually young, injured, sickly or dead specimens, and rodents such as voles. This is believed to be due to a paucity of edible plant life in this sub-Arctic region and a local lack of competing large carnivores (including other bear species). Like brown bears, American black bears try to use surprise to ambush their prey and target the weak, injured, sickly or dying animals in the herds. Once a deer fawn is captured, it is frequently torn apart alive while feeding. If it is able to capture a mother deer in spring, the bear frequently begins feeding on the udder of lactating females, but generally prefers meat from the viscera. American black bears often drag their prey to cover, preferring to feed in seclusion. The skin of large prey is stripped back and turned inside out, with the skeleton usually left largely intact. Unlike gray wolves and coyotes, American black bears rarely scatter the remains of their kills. Vegetation around the carcass is usually matted down by American black bears and their droppings are frequently found nearby. American black bears may attempt to cover remains of larger carcasses, though they do not do so with the same frequency as cougars and grizzly bears. They will readily consume eggs and nestlings of various birds and can easily access many tree nests, even the huge nests of bald eagles. American black bears have been reported stealing deer and other animals from human hunters.
Interspecific predatory relationships
Over much of their range, American black bears are assured scavengers that can intimidate, using their large size and considerable strength, and if necessary dominate other predators in confrontations over carcasses. However, on occasions where they encounter Kodiak or grizzly bears, the larger two brown subspecies dominate them. American black bears tend to escape competition from brown bears by being more active in the daytime and living in more densely forested areas. Violent interactions, resulting in the deaths of American black bears, have been recorded in Yellowstone National Park.
American black bears do compete with cougars over carcasses. Like brown bears, they will sometimes steal kills from cougars. One study found that both bear species visited 24% of cougar kills in Yellowstone and Glacier National Parks, usurping 10% of the carcasses. Another study found that American black bears visited 48% of cougar kills in summer in Colorado and 77% of kills in California. As a result, the cats spend more time killing and less time feeding on each kill.
American black bear interactions with gray wolves are much rarer than with brown bears, due to differences in habitat preferences. The majority of American black bear encounters with wolves occur in the species' northern range, with no interactions being recorded in Mexico. Despite the American black bear being more powerful on a one-to-one basis, packs of wolves have been recorded to kill black bears on numerous occasions without eating them. Unlike brown bears, American black bears frequently lose against wolves in disputes over kills. Wolf packs typically kill American black bears when the larger animals are in their hibernation cycle.
There is at least one record of an American black bear killing a wolverine in a dispute over food in Yellowstone National Park. Anecdotal cases of alligator predation on American black bears have been reported, though such cases may involve assaults on cubs.