Bears are long-lived if they survive their first few years of life. Most mortality occurs in young cubs or dispersing juveniles as a result of food stress. Pre-weaning cub mortality was estimated at 10-30% in polar bears and sub-adult mortality at between 3 and 16%. In American black bears in Alaska, sub-adult mortality was estimated at 52 to 86%. Estimates of longevity in the wild are as high as 25 years. Captive animals have been known to live to 50 years or more (Ursus arctos).
Male and female bears generally associate only briefly for mating. Males monitor the estrus condition of females in their home range and will remain close for a few days when females are receptive. Multiple mating is practiced by both sexes.
Mating System: polygynandrous (promiscuous)
Bears give birth to 1 to 4 young, usually 2, at intervals of 1 to 4 years. There is evidence of delayed implantation in all species. Gestation lengths ranging from 95 to 266 days, with implantation being delayed from 45 to 120 days. Actual gestation lengths may be closer to 60 to 70 days. Births in temperate species occur during the winter when the female is dormant. The cubs nurse during the dormant period and the entire metabolic demands of the female must be met by her fat reserves. Births in Helarctos malayanus may occur at any time of the year. Sexual maturity occurs at from to 3 to 6.5 years old, usually occurring later in males. Growth continues after sexual maturity. Males may not reach their adult size until 10-11 years old. Females reach adult sizes usually around 5 years old.
Females give birth to their young in protected areas, often a den of some kind, until they are capable of getting around well, at several months of age. Bears are very small when born, from 90 (Ailuropoda melanoleuca) to 680 (Ursus arctos) grams at birth. They are born with their eyes and ears closed and are either naked or with only a fine layer of fur. Cubs grow rapidly, polar bears go from 600 grams at birth to 10 to 15 kg within 4 months. Weaning occurs from 3.5 (Ursus thibetanus) to 9 (Ailuropoda melanoleuca) months. Young stay with their mother for up to 3 years, but young of most species disperse after 18 to 24 months. Females are very protective of their young and it is likely that cubs learn about obtaining food and shelter during their extended juvenile time with their mother.
Barcode of Life Data Systems (BOLD) Stats Specimen Records: 389 Specimens with Sequences: 499 Specimens with Barcodes: 300 Species: 12 Species With Barcodes: 11 Public Records: 244 Public Species: 11 Public BINs: 10
Bears have been hunted and persecuted throughout human history. Most bear populations continue to face hunting pressure and have become fragmented as a result of human habitat destruction and hunting.
The IUCN ranks Malayan sun bears (Helarctos malayanus) as data deficient, polar bears (Ursus maritimus) as lower risk, Asiatic black bears (Ursus thibetanus), sloth bears (Melursus ursinus), and spectacled bears (Tremarctos ornatus) as vulnerable, and giant pandas (Ailuropoda melanoleuca as endangered.
Several brown bear subspecies are listed as endangered under the United States Endangered Species Act: Mexican grizzly bears, Ursus arctos nelsoni, European brown bears, U. arctos arctos, and Tibetan brown bears or horse bears, U. arctos pruinosus. Baluchistan bears, Ursus thibetanus gedrosianus, are also considered endangered.
The following species are on Appendix I of CITES: Ailuropoda melanoleuca, Helarctos malayanus, Melursus ursinus, Tremarctos ornatus, Ursus thibetanus, and populations of Ursus arctos in Bhutan, China, Mexico and Mongolia. All other populations of U. arctos are included in Appendix II.
Convention on the International Trade in Endangered Species of Wild Flora and Fauna, 2005. "CITES Appendices I, II, and III" (On-line). Convention on International Trade in Endangered Species of Wild Flora and Fauna. Accessed July 13, 2005 at http://www.cites.org/eng/app/appendices.shtml.
IUCN Species Survival Commission, 2004. "The 2004 IUCN Red List of Threatened Species" (On-line). International Union for the Conservation of Nature. Accessed July 13, 2005 at http://www.redlist.org/.
U.S. Fish and Wildlife Service, 2005. "U.S. Fish and Wildlife Service Endangered Species Program" (On-line). Accessed July 13, 2005 at http://www.fws.gov/endangered/.
Bears are a small group of mostly large mammals, with 8 species in 5 genera (Ursus, Tremarctos, Melursus, Helarctos, and Ailuropoda). Although Ursidae is not diverse, species in this family are widespread and culturally significant to human populations throughout their range.
Flynn, J., J. Finarelli, S. Zehr, J. Hsu, M. Nedbal. 2005. Molecular phylogeny of the Carnivora (Mammalia): Assessing the impact of increased sampling on resolving enigmatic relationships. Systematic Biology, 54: 317-337.
Nowak, R. 1991. Walker's Mammals of the World, Fifth Edition. Baltimore: The Johns Hopkins University Press.
Vaughan, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, 4th edition. New York: Saunders College Publishing.
Bears are often implicated in predation on livestock, although their impact on livestock populations is most often vastly over-stated. This is particularly true of Tremarctos ornatus, which is persecuted for livestock predation despite its primarily frugivorous lifestyle. Bears regularly attack and kill humans when they feel threatened. Females accompanied by their young may be especially aggresssive and unpredictable. Bear attacks that seem at first to be unprovoked, often prove to be inadvertently provoked when investigated. Bears that live near humans, or have become habituated to humans, cause damage by breaking into homes, food stores, and garbage. Some bear species damage crops, such as manioc and corn.
Negative Impacts: injures humans (bites or stings); crop pest
Bears are important members of healthy ecosystems and are sometimes used as indicator species of habitat health and wildness. Bears have also been hunted by humans throughout history for their meat, fat, and fur. Other body parts are used in traditional Chinese pharmacopias, although their usefulness in curing ailments has never been demonstrated. Research on the metabolic pathways black bears use during their winter torpor may help in the development of treatments for kidney failure, gallstones, severe burns, and other illnesses.
Positive Impacts: body parts are source of valuable material; research and education