- How many kinds of bears are there, and where are they found?
- Are bears endangered?
- Are there different varieties or subspecies of black bear?
- Are black bears and cinnamon bears the same kind of animal?
- How can you tell the difference between male and female black bears?
- How do you tell the age of black bears? How long do black bears live?
- What are the sizes and weights of black bears?
- Do black bears have poor vision? Do they have good senses of smell and hearing?
- What kinds of sounds does a black bear make?
- Are black bears good climbers? Are they good swimmers? How fast can they run?
- What is the breeding age of black bears?
- When do black bears mate?
- How long is a black bear's gestation period?
- When are the cubs born?
- How many cubs does a black bear have?
- When do the cubs becomes independent of their mother?
- Do cubs have high annual mortality?
- What do black bears eat? What are the seasonally preferred foods?
- Do black bears prey on other animals?
- What kinds of parasites affect the black bear?
- What kinds of diseases afflict the black bear?
The bear family or "Ursidae" contains 8 species of bears. These include the: (1) American black bear (Ursus americanus), found in Alaska, Canada, forested areas of the lower United States, and in northern Mexico; (2) brown bear (Ursus arctos) (the grizzly and Alaskan brown bears are usually considered to be subspecies of the brown bear), found in northwestern North America, northern Eurasia, and scattered areas of southern Eurasia from the Alps west to the Himalayas; (3) polar bear (Ursus maritimus), found in Arctic and Subarctic areas of Canada, Alaska, Russia, and Greenland; (4) Asiatic black bear (Ursus thibetanus), found from Iran east through India to Vietnam and north through China to Japan; (5) sun bear (Helarctos malayanus), in Indonesia and mainland Southeast Asia; (6) sloth bear (Melursus ursinus), in Nepal, India and Sri Lanka; (7) spectacled bear (Tremarctos ornatus), in the Andes Mountains from Venezuela to Bolivia; and (8) the giant panda (Ailuropoda melanoleuca), in central and western China. Although some books classify the giant panda with the raccoons, or in its own family, the best evidence now indicates that it is a very specialized bear.
References: MacDonald 1984, Wilson and Reeder 1993
Most bears are in trouble in parts of their range. The American black bear was stable or increasing in 33 of 35 states surveyed in 1993. The remaining 6 bear species appear to be in decline over most or all of their range. Human activities are affecting bear habitat for all species-especially those in tropic regions-through commercial and residential development, agriculture, timber harvesting, and oil and gas exploration and development. Direct human threats to bears include the killing of bears through unregulated hunting, protection of property, vandalism, or through commercial exploitation for folk medicine or the pet trade.
The U.S. Fish and Wildlife Service lists the following bears as Endangered (E) or Threatened (T):
- E Giant Panda (Ailuropoda melanoleuca) (China)
- E Brown Bear (Ursus arctos arctos) (Italy)
- E Mexican Brown Bear (Ursus arctos nelsoni) (Mexico) (probably Extinct)
- E Tibetan Brown Bear (Ursus arctos pruinosus) (Tibet)
- E Baluchistan Bear (Ursus thibetanus gedrosianus) (Iran, Pakistan)
- T Louisiana Black Bear (Ursus americanus luteolus) (LA, parts of MS and TX)
- T Brown (Grizzly) Bear (Ursus arctos horribilis) (lower 48 USA)
The International Union for the Conservation of Nature (I.U.C.N.), which has several risk categories, lists the following bears on their most recent Red List of species in need of conservation:
- Baluchistan Bear (Ursus thibetanus gedrosianus) (Critically Endangered)
- Sun Bear (Helarctos malayanus) (Data Deficient)
- Giant Panda (Ailuropoda melanoleuca) (Endangered)
- Mexican Brown Bear (Ursus arctos nelsoni) (probably Extinct)
- Polar Bear (Ursus maritimus) (Low Risk)
- Sloth Bear (Melursus ursinus) (Vulnerable)
- Spectacled Bear (Tremarctos ornatus) (Vulnerable)
- Asiatic Black Bear (Ursus thibetanus) (except Baluchistan Bear) (Vulnerable)
References: Amstrup 2003, Servheen et al. 1999
Sixteen subspecies of black bear are currently listed in the scientific literature. The one found in New England is the first-described or "nominate" subspecies, Ursus americanus americanus. However, it is probable that several-if not most-of these alleged subspecies are invalid. It was once a common practice to "describe" new species or subspecies of animals based on minor physical differences among a small sample of animals. For example, some 87 "species" and "subspecies" of North American grizzly/brown bears have been named in the older literature. In reality, only 2 of these may be valid taxonomic entities.
References: Merriam 1918, Hall 1981, Lariviere 2001
Black bears are typically black overall, with brown muzzles, perhaps brown spots over the eyes, and sometimes a white V or patch on the chest. However, one of the named subspecies of black bear is the so-called "cinnamon" bear (Ursus americanus cinnamonum) described in 1854 by J.J. Audubon and J. Bachman from a specimen taken in Colorado. In reality, brown, cinnamon, and blonde "black bears" occur widely west of the Rocky Mountains. These color phases are nearly identical to those in domestic dogs and appear to be inherited. Brown-phase animals are rare or absent in moist areas of North America but common in arid regions. For example, in Minnesota, 94% of black bears are black, but only 9% in Yosemite National Park. This probably represents natural selection, as influenced by vegetation and habitat type. Bears in dense boreal or mountainous forests or temperate rain forests are predominantly black, while those in more diverse habitats have a greater percentage of alternative colorations. Habitat is likely the dominating factor influencing color phases in black bears.
The unique Kermode ("spirit") bear of coastal British Columbia is a "white" (cream-colored) phase of the black bear (U. a. kermodei). Few kermodei are actually white; ranging from 3 to 12% of the populations on Gribbell, Roderick, and Princess Royal islands and the adjacent mainland. White bears have pigmented eyes and skin and are not albinos. White-phase Kermodes were probably established and maintained by genetic isolation, reduced population size, and possibly selective pressure and non-random mating.
Black and grizzly/brown bears may sometimes be confused in the field, particularly since some "black bears" are brown and some grizzlies nearly black. The identification series of the Montana Department of Fish, Wildlife and Parks is a useful aid to distinguishing the 2 species.
References: Clarke 2002, Herrero 2002, Kolenosky and Strathearn 1987a, Marshall and Ritland 2002, Powell et al. 1997, Rogers 1980, Rounds 1987
Male and female black bears cannot always be distinguished with certainty, unless accompanied by cubs. However, males are typically larger than females. In studies in Idaho and Pennsylvania, adult males weighed nearly twice as much as adult females. In areas of good nutrition, females reach adult weight at 3½ years, but males may continue to grow until 8½ or older. In New York, 2½-year-old males were similar in size to 8½-year-old females. Adult males also have substantially larger skulls than do females. In Alaska, 5-year or older females had skulls 8 to11% smaller than males of comparable age. Adult males have more heavily muscled heads, necks, and shoulders than do females. If adult bears stand erect facing the viewer, it is often possible to see the male's penis or the female's nipples. Males are often called "boars" and females "sows".
References: Alt 1980, Beecham and Rohlman 1994, Landriault et al. 2000, Rausch 1961, Sauer 1975
The "average" age of bears in a given area is difficult to specify, since many tallies are derived from hunter harvest, which can be biased towards the more inexperienced or more vulnerable animals. Although a population should have representatives of all age classes, a mere tabulation of age ratios from a sample of that population conveys little or no information on demographics or rate of increase. Additional information is needed to adequately assess the response of a population to change. In one New Hampshire study, the average ages of live-captured bears were greater than those of hunter-killed animals, while female bears were less abundant in the captured sample than in hunter harvest. It was unknown which result was more representative of the actual population.
Black bears can be long-lived, although animals over 30 years of age are rare. Wild bears have reached 32½ in New York, 33½ in British Columbia, and 35½ in Michigan. The oldest bears recorded in Massachusetts were a 25½-yr-old male and a 26½-yr-old female.
References: Caughley 1974, Gilbert et al. 1978, Kane and Litvaitis 1992, Sauer 1975, Smith 1995, Stoneberg and Jonkel 1966, Willey 1974
Black bear life history summaries have variously reported weights ranging from 88 to 400 lbs. for adult females, and 132 to 617 lbs. for adult males. Lengths have been reported as 51 to 75 inches for adult males and 43 to 67 in. for adult females and shoulder heights at 31 in. for females and 40 in. for males. A tabulation of average and range of lengths and weights from 10 states is shown in the accompanying table. Comparisons should be made with caution. Weights and lengths may vary depending on geography, season of the year, age of the animal, whether the animal was live or field-dressed, and the particular technique or skill of the persons taking the measurements.
Size and Weight of Adult American Black Bears*
|Location||Average Length Male||Range Length Male||Average Length Female||Range Length Female||Average Weight Male||Range Weight Male||Average Weight Male||Range Weight Female|
|Idaho (4 sites)||56-61||51-54||250-280||123-141|
There is an anecdotal report of a 900 lb. black bear killed in Arizona in December 1921; however, this is probably an estimate. The current "world record" black bear was taken by a hunter in North Carolina in November 1998. The 10¾-year-old male weighed 880 lbs. An 856½ lb. male, 7 ft. 9 in. long, was killed by an automobile in Manitoba in August 2001. This bear lost an estimated 30 lbs. of body fluids between time of death and weighing, so it probably would have been a record if promptly weighed. Some Minnesota and Wisconsin bears also have exceeded 800 lbs. The heaviest female black bear was recorded in Minnesota in 1993, and weighed 520 lbs. The heaviest Massachusetts bear was taken in the November 1980 hunting season in Berkshire County. It weighed 467 lbs. field-dressed (>525 lbs. live weight).
References: Alt 1980, Carr 2002, Beecham and Rohlman 1994, Eason et al. 1996, Elowe 1984, Fair and Rogers 1990, Harlow 1961, Hristienko 2001, Jones 1999, Jonkel 1974, Jonkel and Cowan 1971, Kohn 1982, Kolenosky and Strathearn 1987a, Pelton 1982, Poelker and Hartwell 1973, Seton 1929, Sitton 1982, Willey 1978
Black bears probably do have poor vision when compared to humans. However, black bears have color vision and excellent near vision and pattern discrimination. These abilities undoubtedly help the animal forage for small, scattered food items. The bears probably focus on acorns and other food items both by sight and smell. In experiments, black bears have retained memory of specific shapes and patterns for up to 8 months. This ability undoubtedly helps them remember specific food sources over time.
Smell is undoubtedly the most important of the bear's senses. Bears use olfaction both to discern distant odors and to identify objects at close range. Although not tested in the experimental sense, bears can probably identify carcasses from several miles distance. Black bears may stand briefly on their hind legs, possibly to see over vegetation, but also to better scent the person or item that they are sensing. Cubs frequently sniff, lick, and mouth a wide range of plants and other potential food items and may learn these food items by sniffing the mouth and breath of their mother.
Although experiments have not been done, it is likely that black bears have a good sense of hearing. In an Alberta observation, 2 grizzlies heard a elk calf bleating from 1600 feet away and then located and killed the calf. Black bears may well have similar auditory capabilities.
References: Bacon and Burghardt 1976a, Bacon and Burghardt 1976b, Fair and Rogers 1990, Herrero 2002, Kilham and Gray 2002, Kolenosky and Strathearn 1987a
The degree and nature of bear vocalizations depends on the species. Black bears are presumed to be more vocal than brown bears because black bears are a forest species and cannot see long distances. Other forest-dwelling bears, such as spectacled and sloth bears, are also quite vocal. Black bears communicate using a variety of sounds, as well as gestures, stances, and signs or marks. Behaviorists using human-habituated black bears are now learning more about these sounds and the ways in which bears communicate. Cubs "purr", coo, moan, and mew. A bawling and wailing sound or gulps may indicate distress or nervousness. A variety of other bawls, woofs, moans, grunts, bellows, or other sounds may be emitted by bears of various ages and dispositions. Mechanical sounds such as huffing, blowing, snorting, chomping, foot stamping, and "jaw-popping" are commonly produced in response to threats or other stimuli. Despite the popular literature, black bears rarely growl, although some snared or trapped bears may do so.
A common folk belief in New England and northern New York is that black bears "hoot", "holler" or "wail" at night during the fall months. This sound is alleged to be a mating cry, despite the fact that bears breed in summer. There is no scientific basis for attributing these peculiar sounds to black bears. The sounds-if any-are undoubtedly made by other animals, possibly by porcupines.
References: Herrero 1978, Jordan 1976, Kilham and Gray 2002, Kolenosky and Strathearn 1987a, Matson 1967, Rogers and Wilker 1990, Stirling and Derocher 1990, Willey 1978
Black bears undoubtedly evolved as forest animals and are rarely found far from trees. They are excellent climbers and easily ascend trees by hooking or gripping them with their short, narrow claws. Cubs are capable of climbing as soon as they exit their natal den and readily climb in response to intrusion by strange bears or humans. The sow does not need to signal the cubs to climb, although she may readily do so. Cubs can easily climb to 100 feet or more. Black bears of all ages retain the climbing ability, although some old, large males may be reluctant to do so. The bears climb not only to escape a threat but also to rest, sleep, play, nurse, obtain food, or attain shelter.
Black bears are also good swimmers and do not hesitate to enter water, whether to cross a waterway or to bathe or wallow. Two bears translocated to a small island in Newfoundland swam at least 0.6 mile through salt water to return to the capture site. Bears have also been seen swimming in Yellowstone Lake, Wyoming, "miles from shore". In Massachusetts, bears regularly swim across the Connecticut River.
Although black bears sometimes appear to be clumsy and to waddle or amble along, they are capable of fast speed for short distances. Bears have been clocked at speeds of up to 35 mph.
References: Bray and Barnes 1967, Elowe 1984, Herrero 1972, Herrero 1983, Hill 1942, Kolenosky and Strathearn 1987a, Payne 1975, Schullery 1986
The age of first reproduction in female black bears is related to food supply, and hence body size and condition. When foods are abundant, the bears become sexually mature at 2 years and produce their first litter at age 3. However, when nutritionally stressed, females may delay cub production until 5 or even 7 years. In Massachusetts, females typically give birth at 3, although a few delay until 4 years of age. Occasional females in Maryland, New Jersey, and Pennsylvania have bred at 1 year and produced first litters at 2, while in parts of Alaska, Minnesota, and Montana sows sometimes first give birth at 6 to 7 years. Males are capable of breeding at 3 years but may not do so due to competition with larger dominant males.
References: Alt 1980, Bittner 1998, Elowe 1984, Elowe 1987, Fuller 1993, Garshelis 1994, Garshelis et al. 1998, Jonkel and Cowan 1971, Miller 1994, Powell et al. 1997, Rogers 1987a
Female black bears typically come into heat in early June and remain in heat until mated or until the ovaries regress. Peak breeding occurs from mid-June to mid-July, but has ranged from late May to late August in Ontario and early June to early September in Tennessee. The female's receptive period depends on the length between onset of estrus and mating and averaged 10 days in captive bears. Males travel widely during the mating season and probably locate the females by scent. Male-female associations may last for a few hours to 2-5 days. Both sexes are promiscuous and the longer associations probably represent more than 1 male breeding the female. Black bears may be induced ovulators and cubs from the same litter may possibly have different fathers.
Once having bred, female black bears typically give birth every other year. Lactation probably inhibits estrus during the summer when she has dependent cubs. However, if the sow loses her litter prior to the summer mating period, she may mate again and produce another litter in the subsequent year. Females who lose their young after the mating period then skip a year in the breeding cycle. Some bears have bred while raising cubs, but this is atypical.
In some areas, such as Maine and New York, bears may exhibit reproductive synchrony. In one Maine study area, 95% of litters were produced in odd-numbered years following abundant beechnut crops. This synchrony was believed to derive from alternating cycles in beech production in areas lacking alternate fall foods.
References: Barber and Lindzey 1986, Eiler et al. 1989, Erickson and Nellor 1964, Free and McCaffrey 1972, Garshelis 1994, Johnson and Black 1994, Kolenosky 1990, LeCount 1983, McLaughlin et al. 1994, Powell et al. 1997, Seguin 1992
Black bears, like brown and Asiatic black bears and many other carnivores, have a prolonged gestation period resulting from an arrest in embryonic development or "delayed implantation". After mating, the fertilized egg develops into a minute ball of cells or "blastocyst", at which time development stops and the blastocyst remains unattached in the uterus. If the female attains a minimum weight in the fall, usually about 150 lbs. (but perhaps less in the southern states), the blastocyst implants in the uterine wall in late November and embryonic growth proceeds until birth of the small, feeble cubs about 45 to 55 days later. If the female fails to accumulate sufficient fat reserves, the blastocyst fails to implant and pregnancy is terminated.
Delayed implantation has been assumed to convey a selective advantage by allowing the young to be born as early as possible in spring, to avoid mating at an unfavorable time of year, or to ensure synchrony of one or more reproductive processes. The applicability of these hypotheses to black bear is uncertain. Overall, gestation is commonly reported to be 7 to 7½ months, but was estimated at 6½ months in Pennsylvania and was observed to be 182 to 236 days (6-7¾ months) in captive North Carolina bears.
References: Alt 1983, Ammons 1974, Bunnell and Tait 1981, Kolenosky and Strathearn 1987a, Mead 1989, Ramsay and Dunbrack 1986, Wimsatt 1963
Black bear cubs are born between early December and early February; however, actual birth events are rarely observed in the wild. In one Pennsylvania study, 32 litters were born between January 3 to 24, averaging January 15. Newborn cubs are blind, hairless, and weigh about 7 to 10 ounces. They locate their mother's nipples and suckle immediately after birth. Sows usually have 6 functional mammaries. As the cubs grow, they become increasingly active within the den. By mid-March, they may venture a short distance outside and then return. The shortened gestation period and subsequent birth of very small young allows bears to shift from transplacental to mammary nourishment of the young. This is undoubtedly a response to physiological constraints associated with supporting fetal growth while hibernating and avoiding food intake.
References: Alt 1983, Kolenosky and Strathearn 1987a, Powell et al. 1997, Ramsay and Dunbrack 1986
Litter size ranges from 1 to 4 young, averaging from 1.4 in Arkansas to 3.0 in Pennsylvania. First litters may be small, sometimes a single cub. Two or 3 cubs are typical thereafter. Five-cub litters are uncommon; extraordinary litters of 6 cubs have been reported in Manitoba and Pennsylvania. Average litter sizes in 2 Massachusetts study areas were 2.0 and 3.0. Two 5-cub litters have been reported in Massachusetts, once in the den and another in the field. Field observations are probably valid, as natural adoption of cubs is rare.
The sex ratio at birth is usually 1:1. However, the sex of cubs is related to the mother's weight and to litter size. The number of males is usually higher with heavier mothers, but lower as litter size increases. In one Minnesota study, 82% of single litters were male, while only 52% of 3-cub litters were males. One exceptional Massachusetts sow, 13 yrs old and 175 lbs., produced a litter of 5 male cubs.
During the denning period, sows may produce more than 50 lbs. of milk, metabolized from body fat. This milk is rich in fat and protein and nearly twice as high in kilocalories (per 100 ml) than either human or cow milk. Cubs may weigh up to 9 pounds by den emergence. Massachusetts cubs normally reach 13 to 20 lbs. by early July.
References: Alt 1980, Alt 1984b, Clark 1991, Elowe 1987, Hock and Larson 1966, Kolenosky and Strathearn 1987a, McDonald and Fuller 1998, Noyce and Garshelis 1994, Rowan 1947
Young black bears remain with their mother until about 16 to 17 months of age. Family breakup (typically in June) is probably initiated by the mother when she comes into estrus. She probably uses threats or aggression to compel the young to disperse. However, the female often tolerates the presence of her independent offspring within her home range and will avoid the area used by her daughters. Mothers recognize their own daughters and respond to them on that basis. Male yearlings typically disperse from their natal area after a year or so.
Orphaned cubs may be self-sufficient as early as 5½ months, even when handicapped by injury and when captured and released in an unfamiliar area. Both sexes seem to survive equally well. However, in Ontario, only 30% of cubs orphaned during spring survived.
References: Erickson 1959, Fair and Rogers 1990, Kolenosky and Strathearn 1987a, Powell et al. 1997, Rogers 1987a
Cub survival is influenced by food abundance and quality, physical condition of the mother, social factors, litter size, experience of the mother, cub birth weight, and estimation technique. Mothers who are nutritionally stressed, or first-time breeders, are more likely to lose cubs than are well-fed mothers. In Massachusetts, litter order was the principal factor in determining minimum first-year survival. Ten of 12 known first litters had 0% cub survival to 1 year, while 49% of second and later litters had 100% survival through the first year. Since most first litters were born to 3-year-old sows, it is likely that the mother failed to attain the minimum weight necessary to successfully raise cubs.
Annual cub survival throughout North America has varied from 27% on Long Island, Washington, to 90% at Dry Creek, Arkansas. In one Massachusetts study, 65% of female cubs (but only 10% of males) survived until adulthood. A later study in the same area estimated 63% annual survival (sexes combined). These rates are somewhat low compared to studies in Minnesota, Pennsylvania, and Wisconsin and may relate to spring and summer food conditions. Most cub mortality occurs between 2 and 5 months of age. Cannibalism, abandonment, predation, accident, illegal kill, and disease are sources of cub mortality.
References: Bunnell and Tait 1981, Clark 1991, Elowe 1987, Elowe and Dodge 1989, Garshelis 1994, Kolenosky 1990, Lindzey et al. 1986, McDonald 1998, Rogers 1976
Several workers have suggested that the period between den emergence and the availability of summer-ripening fruits and berries is a "negative foraging period" during which bears gather enough food to sustain life, but not to gain weight. However, recent studies in Minnesota challenge this assumption. Young bears can and do gain weight from spring foods. However, lactating females may indeed lose weight due to the high energy demands of milk production. Breeding-age males may also lose weight due to changes in physiology and behavior.
Bears which feed in garbage dumps, campgrounds, or at bait stations may grow faster, attain greater weights, and have greater fertility than their wild counterparts. In the Great Smoky Mountains National Park, both male (224 lbs.) and female (132 lbs.) "panhandler" bears using high-energy human foods were heavier on average than wild bears of the same sex (163 and 110 lbs). Additionally, 56% of panhandler females were lactating, as opposed to 33% of wild sows. Similarly, in Michigan, "dump bears" tended to be heavier than those captured elsewhere, while garbage-fed females averaged 3.1 cubs per litter as compared to 2.0 elsewhere. One 9-yr-old male in northern Minnesota, fed daily at a bait station, grew from 410 to 620 lbs. over a 51-day period.
References: Beecham and Rohlman 1994, Bray and Barnes 1967, Cardoza 1976, Chi et al. 1998, Costello 1992, Eagle and Pelton 1983, Fair and Rogers 1990, Herrero 2002, Kilham and Gray 2002, Kolenosky and Strathearn 1987a, McDonald and Fuller 1994, McLean and Pelton 1990, Noyce 1994, Noyce and Garshelis 1994, Powell et al. 1997, Rogers et al. 1976, Rogers 1976, Rogers and Wilker 1990, Schorger 1949, Seibert 1991, Spencer 1955, Tisch 1961, Warburton 1982
While insects comprise an important part of a black bear's diet, particularly in summer, vertebrate prey is less commonly taken. Black bears will scavenge carcasses of winter-killed deer or other hoofed animals in spring after den emergence. However, most living prey animals are too swift or elusive to be caught by black bears on a regular basis. An exception occurs during a brief period in spring when newborn moose, deer, or caribou young are vulnerable. Black bears were presumed to be the largest source of moose calf mortality when black bear numbers were 10 times greater than brown bears and when black bear densities were greater than 520 per 1000 mi². Predation nearly ceased by the time the calves are 2 months old. However, cow moose will aggressively defend their young against bear attack, and bears may be injured or killed when attempting to prey on moose calves. In Newfoundland, black bears accounted for 35% of caribou calf mortalities, 62% of which occurred within 4 weeks of birth. Black bear have also preyed on mule or white-tailed deer fawns in some areas. A New York study suggested that bear predation on newborn fawns could be a significant factor affecting annual recruitment. Bear predation also accounted for 49% of 21 radio-collared fawn mortalities in northeastern Minnesota. However, a mortality study in western Massachusetts found no instances of black bear predation on white-tailed deer fawns. Predation may be a learned response by black bears and further research is needed. Predation on adult cervids is usually rare; however, in Labrador and Newfoundland, very large males may prey on adult caribou. Livestock predation sometimes occurs.
Black bears will readily eat fish, but usually find them difficult to catch except at runs during spawning season when large numbers of breeding salmon and chars congregate in space and time. Black bears will also scavenge along the shoreline on both the Atlantic and Pacific coasts to find edible food items.
References: Ballard 1992, Ballard 1994, Decker 1991, Kunkel and Mech 1994, Matthews and Porter 1988, Obbard et al. 2000, Ozoga and Verme 1982
Black bears have been reported to host more than 30 external and internal parasites, including coccidian protozoans, flukes, tapeworms, intestinal roundworms, lungworms, filarial worms, lice, fleas, ticks, and mites. Roundworms (Toxascaris sp.) were the most common endoparasite in New York, occurring in 31% of bears sampled. In the Great Smoky Mountains National Park, 90% of bears were infected with the larval form of Dirofilaria ursi, a roundworm related to the dog heartworm. In New York, 46% of bears harbored this parasite.
Trichinellosis, or muscleworm infection, is a parasitic infection of humans (and domestic animals) resulting from the invasion of muscle tissue by the larval stage of the roundworm Trichinella spiralis. Severe muscle pain, fever, edema, localized hemorrhaging, and neurologic problems may result from this disease. Infection results from the consumption of undercooked meat-such as pork-containing encysted larvae. Trichinellosis has also occurred from eating undercooked bear meat. Larval Trichinella were found in 0% of bears sampled in Vermont, 1% in Labrador, 2% in Pennsylvania, 6% in New York, 13% in Idaho, and 22% in Alaska. Although it is commonly believed that bears acquired the parasite from eating garbage, a greater number of infected bears occur in remote areas than those with high human densities. Bears probably acquire the parasite by cannibalizing carcasses of other bears. It has been hypothesized that trichinellosis contributes to antagonistic or erratic behavior in bears. However, there is no conclusive evidence to support this hypothesis.
The protozoan parasite Toxoplasma gondii infects a wide ranges of birds and mammals. This parasite is transmissible to humans and may cause serious or fatal illness in persons with compromised immune systems. Congenital infections may produce birth defects. Wildlife can serve as the intermediate reservoir host for this parasite and cysts can survive for years in muscle tissue. Consumption of infected meat can produce infection in humans. In Pennsylvania, 80% of sampled bears showed antibodies for Toxoplasma. Persons consuming bear meat should cook the meat to an internal temperature of at least 66º C (150º F) for 3 minutes, which is sufficient to kill both Toxoplasma and Trichinella.
There may be individual and regional variation in the susceptibility of black bears to ectoparasites. Ticks were the most common ectoparasite in Idaho. Most bears were lightly infested (<25 ticks). However, in Montana, 100% of 117 bears examined in May and June were infested with ticks (Dermacentor andersoni). Subadult black bears were often in poorer condition than adults and probably more susceptible to parasites. Mange mites (Ursicoptes americanus) were found on 4% of bears sampled in Idaho. Since 1993, about 45 cases of nearly hairless bears (infested with the mite Demodex ursi) have been found on the western edge of Ocala National Forest in Florida.
References: Babbott and Day 1968, Briscoe et al. 1993, Butler and Khan 1992, Forrester et al. 1993, Goad 2003, Jonkel and Cowan 1971, King et al. 1960, Rausch et al. 1956, Rogers and Rogers 1976, Schad et al. 1986, Worley et al. 1983, Yunker et al. 1980
Wildlife diseases do not appear to play a major role in morbidity and mortality of black bear populations. However, routine surveillance is lacking. Bears in Idaho showed antibodies for tularemia (19%), Q-fever (6%), brucellosis (5%), leptospirosis (1%), and other pathogens but none showed serious clinical signs of the diseases. In the Great Smoky Mountains National Park, bears showed antibodies for Leptospira sp. (22%), but tested negative for brucellosis and canine distemper. Bears sometimes show evidence of periodontal disease and dental caries ("cavities").
Black bears rarely contract rabies. Large amounts of virus are necessary to infect the animal and infected individuals show little or no virus in their saliva. Only 10 rabid bears were reported in North America through 1983. Since the onset of raccoon-strain rabies in the Northeast, 1 rabid bear has been reported in New York and none in Massachusetts. Captive or pet bears may be a greater risk. In Iowa, a captive cub at a petting zoo developed acute neurologic signs and died. Initially diagnosed with rabies (but later proved to be false-positive), the animal exposed an estimated 350 persons from 10 states. The initial expense to contact these people and give them post-exposure treatment was substantial.
References: Binninger et al. 1980, Cook and Pelton 1978, Gleason et al. 1999, Rogers 1983