(Ursidae)
Class: Mammalia
Order: Carnivora
Suborder: Fissipedia
Family: Ursidae
Thumbnail description
Medium to large, stocky mammals with fur that may be black, brown, reddish, or white
Size
Adults average 4–5 ft (1.2–1.5 m) and 60–150 lbs (27–70 kg) in body length for sun bears to 8–9 ft (2.4–2.7 m) and 900–1,300 lbs (400–590 kg) for polar bears
Number of genera, species
3–6 genera; 8 (or more) species
Habitat
Wide ranging, including forests, rainforests, tundra, deserts, and swamps
Conservation status
Endangered: 1 species; Vulnerable: 3 species; Lower Risk/Conservation Dependent: 1 species; Data Deficient: 1 species
Distribution
On every continent except Africa and Antarctica, but mainly in the Northern Hemisphere
Evolution and systematics
Although this family has a small number of genera and species, it still has a good share of controversy when it comes to classification. For example, some systematists over the years have placed the giant panda in a subfamily of Ursidae, as it is in this chapter, or in its own family, called Ailuropodidae. The Malayan sun bear, sloth bear, and polar bear are often grouped under the Ursus genus, but sometimes fall under the genera Helarctos, Melursus, and Thalarctos, respectively. Subspecies of the brown bear (U. arctos) are often listed as separate species, including the Alaskan brown bear (U. middendorffi) and the grizzly bear (U. horribilis). In addition, the red panda (Ailurus fulgens) was once listed with the ursids, but is now considered a to be a member of its own family, the Ailuridae, or a sub-family of the Procyonidae, which includes the raccoons.
This chapter uses the following classification:
- giant panda, Ailuropoda melanoleuca
- Malayan sun bear, Helarctos malayanus
- sloth bear, Melursus ursinus
- spectacled bear, Tremarctos ornatus
- American black bear, Ursus americanus
- brown bear, U. arctos
- polar bear, U. maritimus
- Asiatic black bear, U. thibetanus
The family Ursidae is believed to have originated in Asia, and is closely related to the canids (dogs and relatives), procyonids (raccoons and relatives), and ailurids (lesser panda). The giant panda is considered to be the most primitive of the bears. Various evolutionary studies have attempted to determine the relationships of the other bears. Fossil studies seem to indicate that the spectacled bear, which is in the subfamily Tremarctinae, diverged from the remaining bears, which are in the subfamily Ursinae. The fossil record also points to a very close relationship between the Asiatic black and American black bears, and places brown and polar bears close to them evolutionarily. Other studies using mitochondrial DNA and cytochrone-b sequence data have provided clarification, and sometimes challenged, previous conclusions. For example, mtDNA data have indicated that polar bears and spectacled bears are very closely related, and diverged from the ursinids about 2 million years ago. Cytochrome-b data appear to show that the sun bear and American black bear are sister taxa, and are somewhat separated from the Asiatic black bear.
Physical characteristics
Bears are medium to large, powerful mammals with rather short tails and plantigrade feet on stocky limbs. Many bears are dark brown to black, but the fur color is often variable within the species and sometimes even among siblings. Among the American black bear, for instance, black, brown, reddish, and even whitish individuals exist. Some species have distinctive white patches or lines on the face, throat, and/or chest. An example is the spectacled bear, which has whitish rings around its eyes. The polar bear is the only species that consists of all white-furred individuals, although the skin is black to make the best use of the heat from the arctic sun, and the individual outer (or guard) hairs are actually clear rather than white. Some species, such as the brown bear, have longer hair on the shoulders that forms a mane. A few, like the sloth bear, have long fur over much of their bodies.
Their heads are rather large, particularly in some species like the panda, and they have small, forward-facing eyes, and noticeable but usually modest round ears. Their teeth include premolars and molars designed for crushing, and long canines, which together assist their omnivorous diet. The giant panda and spectacled bear have flattened molars suited to their strongly herbivorous diets. The sloth bear, which is particularly fond of termites, has no incisors in its upper jaw. The gap, combined with protrusible and naked lips, allows the bear to suck up the insects. Sun bears have especially long tongues to assist them in attaining honey, a frequent item in their diet.
Bear claws, which are non-retractile, differ in length in separate species. In the brown bear, for example, the light-colored claws stand out from the typically brown fur, and range from 2–4 in (5–10 cm) long. The Asiatic black bear, on the other hand, has comparatively short claws, typically measuring less than 2 in (4–5 cm) in length.
In overall size, bears have a fairly wide range. In all species, males are larger than females. The smallest ursid is the Malayan sun bear, with a body length of 4–5 ft (1.2–1.5 m), and a typical male weight of 60–150 lb (27–70 kg). Polar and brown bears are at the opposite end of the spectrum, with male polar bears averaging 8–9 ft (2.4–2.7 m) in body length and 900–1,300 lb (400–590 kg), and male brown bears 5–8 ft (1.5–2.4 m) and about 350–850 lb (160–385 kg).
Distribution
Bears have a wide distribution in the Northern Hemisphere. Here, the most widely distributed species include the polar bears, which inhabit the circumpolar ice pack; the brown bears, which live throughout northern North American and north to north-central Eurasia; and the American black bear, which stretches from northern Mexico well into Canada. Both the sun bear and sloth bear reside in Southeast Asia. The range of the Asiatic black bear is somewhat larger, extending from Afghanistan to southeastern Russia. The giant panda has the smallest range of all bears, with six small populations known from the Tibetan plateau in southwestern China. The spectacled bear, the only ursid that inhabits in the Southern Hemisphere, lives around the Andes in South America, including sites in Bolivia, Colombia, Ecuador, Peru, and Venezuela.
Habitat
Bears' habitats vary from species to species. The polar bear thrives on the arctic ice pack, a sharp contrast to the tropical rainforests of southeast Asia, where the Malayan sun bear resides. The American black bear's habitat spreads from the woods in western U.S. mountains to wetlands in southeastern states, and to the northern tundra in Canada. In contrast, the shaggy-looking sloth bear opts for grasslands and dry forests from lowlands in India to the foothills of the Himalayas.
The brown bear, also known in parts of North America as the grizzly or kodiak, ranges from thickly forested areas into grasslands and tundra in the Northern Hemisphere, while the spectacled bear prefers lush mountain forests in South America. The giant panda lives in the bamboo forests of China, and the Asiatic black bear in primarily moist forests throughout southern Asia.
Home ranges for bears also vary. Pandas keep to about 2–3 mi2, but brown bears are known to range over 800–1,000 mi2 if the habitat is poor and food is scarce.
Behavior
Little is known about the behavior in the wild of half of the ursid species, mostly due to their remote geographical distribution. These include the spectacled bear, Asiatic black bear, sun bear, and sloth bear. In general, however, bears overall are solitary animals except during mating season or in mother-cub groupings. Occasionally among brown bears, siblings will stay near one another for a year or two after they leave their mother. Although additional research is needed for substantiation, some reports indicate that sloth bears may form social units, and that male sun bears may remain with the mother after she gives birth.
Bears generally maintain home ranges, with the males' ranges frequently overlapping with those of the females. Black bears mark their territories with scent markings or long scratches clawed into trees. Unusually, male panda bears sometimes do their scent marking while standing on their hands. In black bears and several other species, the ranges of male bears may also overlap, but since the ranges are often very large and bears rarely see one another, the overlaps present little opportunity for territorial conflicts. Even when bears come together at one feeding site, such as brown or black bears at a salmon stream, individual bears maintain their personal space and share the resource. When bears approach one another too closely, temporary dominance hierarchies may form, with the largest males mounting short-lived aggressive displays, including growls, and occasional charges to maintain a small feeding territory. During breeding season, males generally compete for females, but the male-female bonds typically only last one or two weeks.
With their large, plantigrade feet and stout limbs, bears are often pictured as lumbering animals that always move slowly and deliberately. They can, however, move very quickly when necessary. Black bears, for example, can run at speeds of 30 mph (50 kph), and polar bears are fast enough to catch caribou on the Arctic tundra. Even the somewhat awkward-moving sloth bear can outrun a human over short distances. Most bears are also accomplished tree climbers. The sun bear has perfected climbing, quickly scaling trees in search of honey and other food items, and even fashioning resting/feeding platforms out of broken branches high up in the trees. Polar bears and adult brown bears (with the exception of some populations in Europe) do not climb, but both are good swimmers. Other bears, like the Asiatic black bear, can also swim. With their large and slightly webbed front feet, polar bears are particularly adept swimmers and divers, and reportedly are able to swim across open-water expanses of up to 100 mi (65 km).
Ursids tend to be crepuscular (mainly active at dawn and dusk) or nocturnal animals, although some extend their active periods into the daytime. Polar bears are an example. While they are most active at night and at dawn, they are frequently seen hunting during the day.
Although ursids do not technically hibernate, many cooler-climate bears do enter winter dormancy, during which the respiratory and heart rates drop, but the body temperature dips only slightly. In the black bear, for instance, their body temperature drops from about 100°F (38°C) to 88–93°F (31–34°C). The Asiatic black bear is an exception: Its body temperature declines precipitously to just 37–45°F (3–7°C). It is during the winter dormancy that female ursids give birth. As she sleeps, the young suckle and grow. Among the cooler-climate species, both males and females become dormant, except in the polar bears, where only pregnant females enter winter sleep. During the winter, bears are capable of awakening, and occasionally leave their winter dens, which may be burrows, hollow logs, or tunnels in the snow and ice. Warm-climate bears, including sun, sloth, and spectacled bears, do not enter winter sleep. Although most brown bears and Asiatic black bears "hibernate," those from warmer climates frequently skip winter dormancy and remain active all year.
Feeding ecology and diet
Bears are omnivores, often eating whatever is available. The polar bear tends heavily toward a carnivorous diet, existing primarily on ringed seals (Phoca hispida), although it will eat berries and vegetation in the summer. Hunting is accomplished either by ambush or active stalking. In the former, the polar bear will simply wait at an ice hole for a seal to surface, then overpower it with one whack of its mighty paw. It reverts to stalking either on land or in the water if it happens to see a seal on the ice or another animal, such as an elk, in the open. With the polar bear's cryptic coloration, it can approach closely enough on land to give chase and sometimes overtake the animal.
Other ursids tend to prefer a greater amount of vegetation than the polar bear, eating fruits, tender stems, and roots most of the time, and supplementing the diet with insects, fish, an occasional small mammal, or carrion. The larger bears, like the brown bear, will sporadically hunt moose, or elk (Alces alces), and other ungulates. The giant panda, on the other hand, is almost exclusively an herbivore, eating little but bamboo leaves, stems and shoots. Sloth bears are unusual in their strong reliance on termites for food, although other bears also eat termites to some extent. Sloth bears, along with the sun bear in particular, are also fond of honey. In both cases, the bears use their claws to rip open termite and bees nests, and get at the reward.
Reproductive biology
Bears' mating systems vary by species; some, such as the spectacled bear, are monogamous. Others, such as the polar bear, are polygamous. Most bears mate in the spring or summer, but the fertilized eggs do not implant in the uterus and begin developing until fall. After this so-called delayed implantation, the eggs begin to develop and the females give birth in the winter. Some species, including the sloth bear, apparently mate year-round in especially warm climates, but due to delayed implantation, all give birth in the winter. Sun bears appear to have delayed implantation, but individuals in zoos have given birth at different times of the year.
Cubs are born small, naked and blind, having developed in the womb for only two to three months. Birth weight ranges from about 11 oz (325 g) in sun bears to 21 oz (600 g) in brown and polar bears. In most cases, females give birth from one to five cubs, although two is the most common litter size among ursids. Panda mothers generally rear only one cub, regardless of the litter size, and the others die. Among cooler-climate bears, the young are born while the mother is in winter dormancy. In warmer-climate species, such as the sun bear, the mother chooses a concealed site, perhaps under branches or thick vegetation, to make a nest for the cubs. Cubs are generally weaned within the first two to five months (pandas wean at about nine months), but remain with the family unit for two to four years, during which the cubs learn to find their own food and hunt while under the protective eye of their mother.
Sexual maturity generally occurs from four to seven years old, but the timing varies among species.
Conservation status
Only one ursid, the panda bear, has been listed as Endangered by the IUCN. Habitat destruction is a major reason for this species' decline. A recent study indicated that not only human population magnitude, but the increasing number of households as family units decrease in size, have contributed to intensifying habitat destruction, particularly for this bear. As the number of households have risen, deforestation and fragmentation of panda habitat have accelerated. Estimates place the total number of pandas in the wild at below 1,000.
Other bears have also experienced decreased suitable habitat and habitat fragmentation. The brown bear, for instance, is now found in only 2% of its former range within the continental United States. The lessened range is blamed in part on habitat destruction and fragmentation. In addition, individual populations of various species have experienced declines, even if the overall species numbers are relatively high. The American black bear is an example. Several subspecies, including Ursus americanus floridanus, are considered threatened locally. To counteract the declines, various hunting bans or regulations, habitat preservation programs, and educational efforts are under way worldwide.
The sloth bear, spectacled bear, and Asiatic black bear are listed as Vulnerable; the polar bear is Lower Risk/Conservation Dependent; and the Malayan sun bear is listed as Data Deficient by the IUCN.
Significance to humans
Various bears are hunted for meat, fur, and trophy mounts. In addition, body parts, such as the gall bladder of sun and American black bears, are also harvested for medicinal purposes, particularly in China. Bears have also become important as attractions at zoos.
While many bears are assumed to be dangerous to humans, bear attacks are few and fatalities are rare.
Species accounts
American black bearBrown bearGiant pandaPolar bearSpectacled bearResources
Books:Craighead, L. Bears of the World. Blaine, WA: Voyager Press, 2000.
Heldmaier, G. and M. Klingenspor, eds. Life in the Cold: The 11th International Hibernation Symposium. New York: Springer-Verlag, 2000.
Kays, R., and D. Wilson. Mammals of North America (Princeton Field Guides). Princeton: Princeton University Press, 2002.
Wilson, D., and Reeder, D. Mammal Species of the World, a Taxonomic and Geographic Reference. 2nd ed. Washington, DC: Smithsonian Institution Press, 1993.
Periodicals:Liu, J., G. C. Daily, P. R. Ehrlich, and G. W. Luck. "Effects of household dynamics on resource consumption and biodiversity." Nature 421 (Jan. 12, 2003): 530–533.
Loucks, C., et al. "Giant pandas in a changing landscape." Science 294 (Nov. 16 2001): 1465
Milius, Susan. "The lives of pandas." Science News 159 (Jan. 27, 2001): 61–3.
Mills, J. "Milking the bear trade (for their bile; sidebar with illustrations and data on bears throughout the world)." International Wildlife 22 (1992): 38–45.
Slattery, J., and S. O'Brien. "Molecular phylogeny of the red panda (Ailurus fulgens)." The Journal of Heredity 86 (November/December 1995): 413–22.
Tyson, P. "Secrets of Hibernation,"
Zhang, Y-P., Ryder, and A. Oliver. "Mitochondrial DNA sequence evolution in the Arctoidea." Proceedings of the National Academy of Sciences of the United States of America 90 (1993): 9557–61.
Organizations
American Bear Association. P.O. Box 77, Orr, MN 55771 United States. Phone: (218) 757-0172. E-mail: admin@americanbear.org Web site:
Great Bear Foundation. P.O. Box 9383, Missoula, MT 59807 United States. Phone: (406) 829-9378. Fax: (406) 829-9379. E-mail: gbf@greatbear.org Web site:
IUCN/SSC Bear Specialist Group. Harry V. Reynolds, Alaska Dept. of Fish and Game-Fairbanks, 1300 College Rd., Fairbanks, AK 99701 United States. Phone: (907) 459-7238. Fax: (907) 459-9723. E-mail: harry_reynolds@fishgame.state.ak.us Web site:
Ursus International Conservation Institute. P.O. Box 832, Pincher Creek, Alberta T0K 1W0 Canada. E-mail: info@ursusinternational.org Web site:
Other
Animal Diversity Web. University of Michigan Museum of Zoology.
The Bear Den.
Bears.org.
Hilton-Taylor, C., (comp.) 2000 IUCN Red List of Threatened Species. IUCN/SSC: Gland, Switzerland and Cambridge, UK, 2000.
Nowak, R. "Black, Brown, Polar, Sun, and Sloth Bears." In Walker's Mammals of the World Online. The Johns Hopkins University Press, 1995.
National Science Foundation. Press release NSFPR 03-06. Jan. 12, 2003. "Researchers Tie Worldwide Biodiversity Threats to Growth in Households: Pandas in China face encroachment, as do other species in global hotspots."
Smithsonian National Museum of Natural History.
[Article by: Leslie Ann Mertz, PhD]