American Bison, Bison bison
TAXONOMY & NOMENCLATURE
(Buntjer et al 2002) (Guthrie 1970) (Meagher 1986) (McDonald 1981) (Prusak et al 2004)
Describer (Date): Linnaeus 1758. Systema Naturae for Bison bison
Taxonomic History and Nomenclature
Order: Artiodactyla* (Even-toed hoofed animals: includes pigs, sheep goats, cattle, deer)
Family: Bovidae (Cattle, water buffalo, bison, antelopes, goats, sheep and more)
Species: Bison priscus (extinct Steppe Bison)
Species: Bison latifrons (extinct Long-horned Bison)
Species: Bison antiquus (extinct Ancient Bison)
Species: Bison bison (American Bison)
Subspecies: Bison bison bison (American Plains Bison)
Subspecies: Bison bison athabascae (American Wood Bison)
Species: Bison bonasus (European Bison)
Subspecies: Bison bonasus bonasus (Lowland Bison)
Subspecies: Bison bonasus caucasicus (extinct in 1925)
Subspecies: Bison bonasus hungarorum (extinct Hungarian Bison)
*New anatomical and DNA evidence on the relationship between Artiodactyla (even-toed ungulates) and Cetacea (whales and dolphins) recently led to a merging of the two orders into a new group, Cetartiodactyla (Montgelard, 1997; reviewed in Kulemzina, 2009). As of October 2012, experts had not agreed on whether to define Cetartiodactyla as an official taxonomic order that would replace Artiodactyla and Cetacea. Some continue to list bison in the order Artiodactyla (Franklin, 2011) or use the term Cetartiodactyla without defining it as an order (IUCN, 2008).
- Scientific name: Bison comes from the Latin word "bison" meaning "wild ox".
- Originally named Bos bison by Linneaus, for its likeness to cattle.
- Despite the many anatomical similarities between extinct and modern bison, in 1825 Cuvier distinguished three bison species (McDonald 1981):
- living European bison
- living North American bison
- an extinct American bison
- Some 14 North American species were
named prior to 1852 when Leidy studied available specimens and described two fossil species and recognized one living species of bison.
- Bison taxonomy underwent a long period of taxonomic splitting that resulted in some 10 fossil species recognized in North America by Skinner and Kaisen in 1947. (McDonald 1981)
- This taxonomy in great need of revision and clarification (McDonald 1981) (Prusak et al 2004)
- Some authorities have classified bison with the cattle genus Bos, other authorities do not. (Nowak 1999) (Prusak 2004)
- Relationship of modern American bison and the European bison is unclear at present, but both are quite similar genetically and can interbreed; despite this fact, they should still be considered separate species. (Prusak et al 2004)
- Modern North American bison have two recognized subspecies: the American Plains Bison (B. b. bison) and the American Wood Bison (B. b. athabascae). (McDonald 1981)
(Prusak et al 2004)
- Even-toed hoofed mammals trace their ancestry back to at least 45 million years ago (Eocene).
- Bison diverged from cattle a few million years ago or less; phylogenies are
poorly understood due to much genetic variation within species. (Buntjer et al 2002)
- The Bison genus first appeared in southern Asia, around 2 million years ago (McDonald 1981)
- Bison priscus was the ancestor of at least some of the North American bison.
(Prusak et al 2004)
- This species flourished in northern Eurasia and Alaska and may have been the dominant hoofed mammal there (Guthrie 1970)
- Bison immigrated to North America several times in the Pleistocene Epoch during times of low sea levels when exposed land connected North America and Asia.
- B. latifrons appeared by 500,000 years ago in North American and survived until around 20,000 years ago.
- The first appearance of B. antiquus in North America was around 250,000 years ago. (Jefferson 2001)
- The B. antiquus line may have led to modern American Plains Bison (Prusak et al 2004)
- McDonald (1981) suggests this speciation occurred around 5,000 years ago.
- European bison may be descendants of Pleistocene bison that returned to Europe from North America.
(McDonald 1981) (Prusak et al 2004)
- B. latifrons became extinct around 20,000 years ago. (McDonald 1981)
- All bison nearly became extinct in North America at the end of the Pleistocene when much of the other megafauna did become extinct
- Modern bison in America (Bison bison) and Europe (Bison bonasus) are genetically very closely related. (Prusak et al 2004)
DISTRIBUTION & HABITAT
(McDonald 1981) (Meagher 1986) (Nowak 1999)
Distribution (of North American bison)
American bison historical distribution. Click on map
for current detailed distribution (IUCN).
From IUCN Bison bison fact sheet.
- Beginning around 5,000 years ago, Bison bison occupied grasslands and parklands of central United States and Canada.
- Wood Bison (B. b. athabascae) mainly inhabited western forests of Canada to eastern Alaska.
- Plains Bison (B. b. bison) in general occupied territories to the south of the Wood Bison, south across the United States to northern Mexico.
- By around 2,000 years ago Bison bison reached its maximum range. (Meagher 1986)
- When modern Europeans arrived in North America, an estimated 50 million bison inhabited the continent.
- By 1903, fewer than 2,000 were known to survive in zoos and private collections, plus isolated wild populations in Canada and the United Sates.
- Occur today in geographically isolated populations in parks and preserves.
- Largest free-ranging populations:
- In Canada (Mackenzie Sanctuary, Wood Buffalo National Park and Slave River lowlands)
- In the United States (Yellowstone National Park)
- American Wood Bison
(B. b. athabascae) occupied boreal parklands and woodlands of Canada and northern U.S.
- American Plains Bison
(B. b. bison) occupied more open grasslands, mainly in the central U.S.
(Buchholtz & Sambraus 1990) (Guthrie 1990) (Lott 1974, 2003) (Meagher 1986) (McDonald 1981) (McHugh 1958)(Nowak 1999)
Body Weight: Males 544 - 907 kg (1,199 - 2,000 lb); females 318 - 545 kg (701 - 1,202 lb); Woods Bison generally larger and heavier than Plains Bison, but much overlap (McDonald 1981)
Body Length: Males 3,040 - 3,800 mm (10 - 12 ft); females 2,130 - 3,180 (7 - 10 ft)
Height at Shoulder: Males 1,670 -1860 mm (5.5 - 6.1 ft); females 1,520-1,570 (5 - 5.1 ft)
Tail Length: Males 330 - 910 mm (1.1 - 3 ft.); females 300 - 510 mm (1.0 - 1.7 ft)
Horns: Arch backwards and upwards with points aimed somewhat inwards. (Grzimek 1990)
- A large headed, massive, tall but narrow-bodied
bovid with a pronounced shoulder hump, short and robust legs, brown hair with a black nose, lips, tongue, hooves and horns.
- 32 teeth in total: 12 molars, 12 premolars, 2 canines, 6 incisors
- Teeth high crowned (hypsodont) and cresent-cusped ("moon tooth" or selenodont)
- All deciduous teeth present at birth
- First permanent tooth erupts during first year
- In general, more luxuriant and longer than the European bison (Nowak 1999)
- Brown; appears black from a distance
- Head, underbelly, flanks, and rear are dark brown
- Longest hairs on forelegs and beard
- Males swing their "pantaloons" in threat displays (Lott 1974)
- Thick mat of hair on the male's forehead helps protect from the head-clashing impacts (Guthrie 1990)
- Winter coat is wooly under fur overlain
by coarse guard hairs; this hair bleaches to tan
- Molt begins in late winter/early spring
- Heavier, denser, and finer pelage than in many cattle
- Have ten times the number of cattle's primary hairs per square inch
- Pelage enables these animals to withstand subzero, windy winters
- Short eyelashes compared to cattle help keep their eye lids from accumulating ice
- Young are much lighter colored than adults.
- This difference follows a general rule for young of animals that live in large groups in open environments where the young need to be protected.
- European bison (B. bonasus) living in smaller groups have young that are colored more like the adults.
Other Physical Characteristics
- Males up to two-thirds larger than females with stouter, more robust and evenly curving horns, a much larger hump, longer pelage, and a thicker neck.
- Considering fossil species of bison and the two species living in North America and Europe today, Bison bison bison has a moderate amount of sexual dimorphism, the European Bison bonasus a low amount, and the fossil Steppe Bison had extreme dimorphism, especially in the size of the skull. (Guthrie 1990)
- Acute sense of smell
- Good eyesight; can recognize objects the size of a horse with a rider at 1 km (.6 mi)
and moving objects at 2 km (1.2 mi). (McHugh 1958)
- Strong head-to-head impacts from dominance fighting between bulls are made less damaging to the brain by a system of bone struts which divide the inner and outer walls of the skull. (Guthrie 1990)
BEHAVIOR & ECOLOGY
(Guthrie 1990) (Lott 2002) (McHugh 1958) (McMillan 2000) (Meagher 1973, 1986) (Mooring 2006) (Nowak 1990) (Powell 2006)(Roden et al 2004) (Van Vuren 1983)
- Active during day (diurnal). Intermittent grazing and ruminating throughout a day, led by a cow.
- Move about 3 km (1.9 mi) per day, but varies according to habitats, presence of biting insects, water. (Meagher 1986)
- Several times a day in summer, engage in wallowing to put dirt and dust into their hair (keep insects off the skin, protect against heat) (Lott 2002)
- Plains Bison are non-territorial and are nomadic
- Plains bison living in small herds may be non-migratory
with fidelity to a home range (Guthrie 1990)
- When free-ranging, are seasonally migratory, moving to lower or more southerly habitats in winter. (Nowak 1999)
- Distances traveled between winter and summer territories may be up to 40 km (24.9 mi) in mountainous habitats and 240 km (149 mi) in boreal-forest parkland habitats. (Meagher 1986)
- Bison are gregarious, forming fluid groups of females with calves, young males up to 2 or 3 and possibly a few older males.
- Breeding age males play no role in calf raising and normally do not mix with the cow and calf groups
- Males live alone or in small herds of males.
- Groups of adult females with their young in one study of free-ranging individuals in Montana averaged 57 individuals. (Nowak 1990)
- Dominance in males is linear
- Top bull dominates over all of group
- Bull with 2nd most dominant role dominates over all the group except for the top bull.
- This pattern continues down the ranking, so that subordinate males only rarely challenge the order
- Dominant bulls have higher cortisol levels, indicating that their social status makes for significant physiological stress during rut. (Mooring et al 2006)
- Dominance strongly correlates with age and weight in bachelor groups (Roden et al 2004)
- Bison are nomadic, may move several miles a day while feeding. (Lott 2002)
- Amount of movement influenced by quality of habitat's plants, presence of biting insects, amount of water available (Meagher 1986)
- Bison herds moved 3.2 km/day in a montane valley to 2.8 km/day in coastal scrub-grassland (Meagher 1986)
- In shrub-steppe habitats of Southern Utah, herds remained in one area about 2 days. (Van Vuren 1983)
- About 5 to 10 percent of bulls' challenges lead to fights. (Lott 2002)
- When bulls threaten, they may bellow, stamp feet and snort, approach each other with tails high (Lott 2002)
- When fighting, bulls run together, clash heads, then push upwards with heads held low. (Lott 2002; Guthrie 1990)
- Cattle fight in a different way, by hooking with horns, then pushing. (Guthrie 1990)
- Relatively short horns of B. b. bison allow a bull to slip to the side after head clashing and gore an opponent; such wounds are frequent (Guthrie 1990)
- Bulls may approach closely, heads turned sideways, then nod the head up and down until one may attack or submit before an attack; called a "nod threat" (Lott 2002)
- Turning the head sideways when two bulls threaten as they face each other, indicates submission; then the contest is over and the winner does not attack. (Lott 2002)
- Play behavior peaked at dusk for young bison. (McHugh 1958)
- Young bison play more than adults. (McHugh 1958)
- Young often engage in wallowing during play (McHugh 1958)
- Juveniles chase, play-mount, butt heads (but don't lower heads when doing so)
- Broadside threat posture displays give best view of overall large body size; may intimidate opponents into submission (Lott 2002)
- Bulls may bellow when threatening each other.
- This sound has been compared to a lion's roar and can be heard up to 5 km (3 mi) away. (Meagher 1986) (Buchholtz & Sambraus 1990)
- Males that are competing with each other may wallow, then urinate in the wallow and roll in the urine before resuming their challenges (Lott 2002)
- Females have also been observed urinating into wallows and rubbing their necks on the soil.
- Bulls use a lip curl and tongue (flehmen) to transfer cow's hormone-packed urine to a receptor organ in the roof of his mouth. (Lott 2002)
- Gaits include walking, trotting, galloping, bounding. (McHugh 1958)
- Can run up to 60 km/hr (35 mph)
- Known to leap over barbed wire fences; surprising agility for animal its size
- Good swimmers; can swim rivers at least 1 km (.6 mi)
wide. (Meagher 1986)
- Bison grazing in Flint Hills of Kansas increased abundance of Upland Sandpipers, Grasshopper Sparrows and together with the effects of recent prescribed burnings, lowered numbers of Dickcissel. (Powell 2006)
- Human prescribed burning plus intense bison grazing may lower numbers of four grass-dependent species of sparrows and Eastern Meadowlarks, and shrub-dependent Bell's Vireos. (Powell 2006)
- After grazing by bison, there are fewer plants, but more species; grazing increases diversity of grassland species, as does a fire. (Lott 2003) (Powell 2006)
- Grazing bison keep grasses short, which promotes prairie dog colony survival; prairie dogs don't live in areas with tall grass where they can not see approaching predators. (Lott 2003)
- Bison are attracted to bare dirt for dusting fur in prairie dog towns.
- Brown-headed cowbirds (Molothrus ater) forage on insects disturbed by grazing bison.
- Sedges and rushes (water loving plants) grow in compacted bison wallows that can hold extra rainfall. (Lott 2003)
- Many other ungulates co-exist with bison using different foraging techniques and plant preferences
- Native Americans living in bison habitats depended on bison for much of their subsistence.
- Bison fertilize the grasslands.
DIET & FEEDING
(Guthrie 1990) (Hawley et al 1981) (Peden et al 1974)
- Bison are grazers; feed mostly on grasses.
- Winter/summer diets differ in free-ranging populations.
- Add lichens and mosses to diet in winter.
- When feeding on natural vegetation select many different grass and a few other plant species, varying with local habitats (Peden et al 1974)
- Blue gramma (Bouteloua gracilis), sand dropseed (Sporobolis cryptandrus) little bluestem (Andropogon), windmill grass (Chloris), wild oats (Avena), wheatgrass (Agropyron), and Bromus Hierchloe, Elymus, Koeleria, Stipa, Phragmites, Distichlis, Hordeum, and Carex.
- In Arizona bison ate 71% saltbush (Atriplex sp.) (Peden et al 1974)
- Ruminant digestive system; four chambered stomach
- Compared to cattle, bison extract more nutrition from low protein, highly fibrous plants. (Hawley 1981).
- European bison have more browse in their diet in the wild. (Peden et al 1974)
- Because American bison males in the wild lived mostly apart from the large herds, they were able to select the better-quality food and grow to very large size. (Guthrie 1990)
REPRODUCTION & DEVELOPMENT
(Berger 1992) (Buchholtz & Sambraus 1990) (Rutberg 1986) (Komers et al 1994) (Lott 2002) (Meagher 1986) (McDonald 1981) (Mooring et al 2006) (Nowak 1999) (Weigl 2005)
- June - September for breeding season
- Males, both solitary and ones from male groups, join females in breeding season (Buchholtz & Sambraus 1990).
- Males are in rut approximately four weeks July-August (Mooring et al 2006)
- A female about to be receptive may run through the herd, attracting the attention of males who compete for rights to tend (Lott 2002)
- Female estrous cycle is 21 days; estrus lasts 9-28 hours (Nowak 1999)
- Cows may select a suitor that is not the highest ranking male. (Buchholtz & Sambraus 1990).
- Courting bulls are not very aggressive towards females.
(Buchholtz & Sambraus 1990).
- Dominant bulls tend (stay with) females that are in estrus.
- Less experienced males also may tend females, but the females may not be in estrus.(Komers et al
- Tending bonds may may exist a few seconds or up to a few days and may or may not result in insemination. (McDonald 1981)
- Copulation occurs about 3 days after rut begins and may be repeated up to four times in a single day.
(Buchholtz & Sambraus 1990).
- 285 days (Haugen, 1974) but may vary for pregnant cows in good condition in the wild in order to allow calves to be born at the same time as other calves in the herd. ( Berger 1992)
Infant (< 1 year old)
- Calves are precocial - can walk 10 minutes after birth
- 99% of all births are of a single calf
- Calves weigh 15 - 25 kg (33-
- At birth bison have all their deciduous teeth in place
- Nursing continues for 7 to 9 months (Rutberg 1986)
- Bull calves are weaned at about 6 months. (Lott 2002)
- Both sexes generally reach sexual maturity between 2 - 4 years. (Nowak 1999)
- Females can conceive as yearlings; more commonly at 2 to 4 years
- Physical maturity for males around 6 years; for females 3 years. (Nowak 1999)
- 10 years in wild (Nowak 1990)
- Several institutions have kept bison for between 20 and 35 years. (Weigl 2005)
- 40 years maximum potential longevity (Nowak 1990).
- Wolves commonly prey on calves.
- Harsh winter weather commonly kills many bison.
DISEASES AND PATHOLOGY
(Buchholtz & Sambraus 1990) (Dragon et al 1999) (Joly & Messier 2004) (Lott 2002) (Taylor 1996) (Weiss et al 2008)
- Bovine tuberculosis (Mycobacterium bovis),
- In one herd at Wood Buffalo Park, estimated to cause 5 percent per year mortality (Fuller 1962)
- This disease was introduced to populations of Canada's B. b. athabascae by imported B. b. bison (Buchholtz & Sambraus 1990).
- Brucellosis abortus was introduced in the bison population in Yellowstone Park and also in
Canada's Wood Buffalo National Park (Joly & Messier 2004)
- The infection is not dangerous to bison cows or cattle; only an occasional fetus dies (Lott 2002)
- Bison, elk, and cattle can all be infected with brucellosis as can many other mammals, birds, and even insects (Lott 2003)
- Intense conflicting opinions exist as to what should be done about this disease. (Lott 2002)
- Bacillus anthracis
infects bison through air-borne dust from contaminated soil. (Lott 2002)
- Bison are very susceptible, as are cattle; infections are often fatal, in as little as two or three days.
- This pathogen may have been introduced to bison in northern Canada during the early 1900's. (Dragon et al 1999)
- Genetic study of this pathogen in Canada and the United States shows it is closely related to B. anthracis that infects domestic cattle but that separate strains may infect bison from northern Canada. (Dragon et al 1999)
- In one study of northern Canada bison, sexually mature males were the most likely to become infected and die in late summer. Perhaps their immune system is already stressed by rutting efforts. (Dragon et al 1999)
- Bison experience much less tick predation than elk or moose in the same habitats (Lott 2002)
(Dermacentor albipictus) suck blood of bison hosts. Calves groom 16 times more often than adults, because they can least afford to loose enough blood to feed a tick. (Lott 2002)
- Pasteurella, an infectious bacterial disease,
found in free-ranging bison herds. (Taylor 1996)
- Managed herds can be vaccinated against this pathogen ( Heddleston & Wessman 1973)
- A record in Ohio of Parelaphostrongylus tenuis (Weiss et al 2008)
- This small parasitic nematode infected bison's brains and spinal cords
- This pathogen's known host is mainly white-tailed deer and also elk.
- Many hoofed animals are known to be susceptible, especially moose who share deer habitats.
(Grizmeck 1990) (Marris 2009)
- Captive Breeding
- An estimated 1 million bison on private ranches and farms in North America. (Marris 2009)
- Bison and domestic cattle can interbreed, producing infertile offspring. (Grizmeck 1990)
- Some 65 Plains bison have been kept at the San Diego Zoo since the first two arrived in 1925. (Towne 1976)
- 14 bison from the San Diego Zoo were released in 1973 at the Marine Corps base Camp Pendelton in southern California (Towne 1976)
and still roam free today.
POPULATION AND CONSERVATION STATUS
(Grizmek 1990) (Halbert & Derr 2007) (Lott 2002) (Marris 2009) (McDonald 1981)(Nowak 1999)
- Prior to 1800's: estimated 50 million B. bison bison in North America
- Late 1800's: bison in North America were nearly extinct.
- 1889: 835 bison living in the United States (Grzimek 1990)
- 1891: Wood Bison (Bison bison athabascae) offered legal protection by Canadians
- 1905: American Bison Society founded at New York city's Bronx Zoo; Theodore Roosevelt
was honorary president,
- 1920's: Wood Bison (B. b. athabascae)numbered around 1,500
- 1920's: 6000 Plains bison introduced to Wood Buffalo National Park in Canada, transmitting bovine tuberculosis to Wood Bison
- 1957: A small wild population of B. b. athabascae discovered in Canada's Wood Buffalo Park (Nowak 1990)
- 1979: Wood bison classified as endangered
- 1988: Wood bison downlisted to threatened
- 2008: About 150 free-ranging bison live at the 125,000 acre Camp Pendleton in southern California. These animals descend from 14 individuals donated in 1973 by the San Diego Zoo.
- ISIS captive population https://app.isis.org/abstracts/abs.asp
- Fewer than 10,000 animals in free-ranging populations (Lott 2003)
Threats to survival
- IUCN Status:
Bison bison is near threatened with stable population trends. (IUCN Red List 2008);
Version 3.1 (http://www.iucnredlist.org/search
- CITES Status: (Subspecies athabascae only) Appendix I as of 07/01/75 - Endangered, no international trade; Appendix II as of 09/18/97 - Not now threatened but may become so if trade not controlled. (97http://www.cites.org/eng/resources/species.html)
- Habitat loss
- Hunting in 1800 and 1900's nearly exterminated bison in North America.
- Their gene pool experienced a bottleneck but genetic diversity hasn't declined significantly.
- Some researchers argue that bison will increasingly be eradicated by genetic modification as they are domesticated.
- Over 90 percent of bison in North America are "undergoing domestication'" (Lott 2002)
- Cattle genes found in nearly more than half of public herds in the U.S. and Canada and in all but one of 50 sampled private herds. (Halbert & Derr 2007)
Important Web Resources:
- Center for Bison Studies at Montana State University - Bozeman: This website offers many links to books and articles about bison.
© 2009 San Diego Zoo Global. Last update March 2009. Disclaimer: Although San Diego Zoo Global makes every attempt to provide accurate information, some of the facts provided may become outdated or replaced by new research findings. Questions and comments may be addressed to email@example.com.
Return to the Fact Sheets page