Bos bison - (Linnaeus, 1758)
American Bison
Other English Common Names: Bison
Synonym(s): Bison bison
Taxonomic Status: Accepted
Related ITIS Name(s): Bison bison (Linnaeus, 1758) (TSN 180706)
French Common Names: bison
Unique Identifier: ELEMENT_GLOBAL.2.101908
Element Code: AMALE01010
Informal Taxonomy: Animals, Vertebrates - Mammals - Other Mammals
Image 7543

© Larry Master

Kingdom Phylum Class Order Family Genus
Animalia Craniata Mammalia Artiodactyla Bovidae Bos
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
Concept Reference: Jones, J. K., Jr., R. S. Hoffman, D. W. Rice, C. Jones, R. J. Baker, and M. D. Engstrom. 1992a. Revised checklist of North American mammals north of Mexico, 1991. Occasional Papers, The Museum, Texas Tech University, 146:1-23.
Concept Reference Code: B92JON01NAUS
Name Used in Concept Reference: Bos bison
Taxonomic Comments: Some authors regard New World B. bison and Old World B. bonasus as conspecific; they were regarded as separate species by Meagher (1986) and Grubb (in Wilson and Reeder 1993, 2005).

There has been some difference of opinion as to whether the two subspecies, B. b. bison and B. b. athabascae, are worthy of recognition; different types of data suggest different conclusions (see Bork et al. 1991). van Zyll de Jong (1986) found that cranial and post-cranial skeletal data indicate a phenotypic discontinuity between grassland and woodland populations and concluded that recognition of the subspecies bison and athabascae is fully justified. External phenotypic data support this distinction as well (van Zyll de Jong et al. 1995). See Geist (1990, 1991) for a summary of evidence that there are no taxonomically valid differences between wood and plains bison. MtDNA data (Polziehn et al. 1996) indicate that both the plains bison (subspecies bison) and the wood bison (subspecies athabascae) form polyphyletic groups; neither is a well-defined taxon. Gates et al. (2001), however, argued that mtDNA data are not appropriate for determining the relationship between the two groups. Wilson and Strobeck (1999) investigated variability in 11 microsatellite loci of bison genomic DNA and concluded that the genetic clustering of wood bison indicates that they are functioning as a genetic entity separate from plains bison. Grubb (in Wilson and Reeder 2005) did not recognize any subspecies.

The generic allocation of this species is debatable. Mitochondrial and ribosomal DNA analyses, together with reproductive, cranial, and other molecular data, strongly indicate that the genus Bison should be treated as a synonym of Bos rather than as a distinct genus in the tribe Bovini (Miyamoto et al. 1989, Wall et al. 1992). Baker et al. (2003) listed the bison as Bos bison. Without explanation, Grubb (in Wilson and Reeder 2005) recognized Bison and Bos as distinct genera.

See Georgiadis et al. (1991) for a phylogeny of the Bovidae based on allozyme divergence among 27 species. See Kraus and Miyamoto (1991) for a phylogenetic analysis of pecoran ruminants (Cervidae, Bovidae, Moschidae, Antilocapridae, and Giraffidae) based on mitochondrial DNA data.
Conservation Status

NatureServe Status

Global Status: G4
Global Status Last Reviewed: 04Apr2016
Global Status Last Changed: 19Nov1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G4 - Apparently Secure
Reasons: Occurs as wild, free-ranging populations in only small fragments of the once vast range in North America, but the species is secure globally due to the many managed populations on public and private lands.
Nation: United States
National Status: N4 (05Sep1996)
Nation: Canada
National Status: N3N4 (09Sep2011)

U.S. & Canada State/Province Status
United States Alabama (SX), Arizona (SNA), Arkansas (SX), California (SNR), Colorado (SX), Delaware (SX), District of Columbia (SX), Florida (SX), Georgia (SX), Idaho (SH), Illinois (SX), Indiana (SX), Iowa (SX), Kansas (SX), Kentucky (SX), Louisiana (SX), Maryland (SX), Massachusetts (SX), Michigan (SX), Minnesota (SX), Mississippi (SX), Missouri (SX), Montana (S2), Nebraska (SX), Nevada (SX), New Mexico (SX), New York (SX), North Carolina (SX), North Dakota (SX), Ohio (SX), Oklahoma (SX), Oregon (SX), Pennsylvania (SX), South Carolina (SX), South Dakota (S3), Tennessee (SX), Texas (SH), Utah (S2), Virginia (SX), Washington (SX), West Virginia (SX), Wisconsin (SX), Wyoming (S1)
Canada Alberta (SNR), British Columbia (S3), Manitoba (SX), Northwest Territories (S2), Saskatchewan (S3), Yukon Territory (S2S3)

Other Statuses

Implied Status under the U.S. Endangered Species Act (USESA): PS
Comments on USESA: Subspecies athabascae in Canada is listed by USFWS as Threatened (Federal Register, 3 May 2012).
Implied Status under the Committee on the Status of Endangered Wildlife in Canada (COSEWIC):T,SC
Comments on COSEWIC: The Plains Bison is designated Threatened and the Wood Bison is designated Special Concern.
IUCN Red List Category: NT - Near threatened

NatureServe Global Conservation Status Factors

Range Extent: 20,000-2,500,000 square km (about 8000-1,000,000 square miles)
Range Extent Comments: Formerly widespread in North America from Alaska and western Canada across U.S. into northern Mexico. Currently found in isolated units throughout and external to historical range.

Number of Occurrences: 21 - 80
Number of Occurrences Comments: A few wild remnant populations occur in U.S. and Canadian national parks. Now occurs mainly as reintroduced, confined populations in many public and private parks and preserves in the U.S. and Canada.

Population Size: 10,000 to >1,000,000 individuals
Population Size Comments: North American population may have been about 30-60 million about the time modern man arrived. Reduced to about 1650 by 1903. Population in 1983 was estimated at 75,000 (Meagher 1986). In Yellowstone NP, the herd was estimated at 3000-3500 in 1996 (Keiter 1997); however, over 1000 were killed during the winter of 1996-97 by agency personnel.

Overall Threat Impact Comments: Susceptible to livestock diseases, though these do not pose a major threat to bison populations. "Control" by agencies may be detrimental to relatively free-ranging herds, such as in Yellowstone National Park.

Short-term Trend: Relatively Stable (<=10% change)

Other NatureServe Conservation Status Information

Inventory Needs: Monitor populations, especially those that are harvested; determine demographics, production, and mortality.

Protection Needs: Maintain existing EOs.

Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) Formerly widespread in North America from Alaska and western Canada across U.S. into northern Mexico. Currently found in isolated units throughout and external to historical range.

U.S. States and Canadian Provinces
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States ALextirpated, ARextirpated, AZexotic, CA, COextirpated, DCextirpated, DEextirpated, FLextirpated, GAextirpated, IAextirpated, ID, ILextirpated, INextirpated, KSextirpated, KYextirpated, LAextirpated, MAextirpated, MDextirpated, MIextirpated, MNextirpated, MOextirpated, MSextirpated, MT, NCextirpated, NDextirpated, NEextirpated, NMextirpated, NVextirpated, NYextirpated, OHextirpated, OKextirpated, ORextirpated, PAextirpated, SCextirpated, SD, TNextirpated, TX, UT, VAextirpated, WAextirpated, WIextirpated, WVextirpated, WY
Canada AB, BC, MBextirpated, NT, SK, YT

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at

Range Map Compilers: NatureServe, 2003

U.S. Distribution by County Help
State County Name (FIPS Code)
MT Carbon (30009), Gallatin (30031), Lake (30047), Park (30067), Sanders (30089), Stillwater (30095), Sweet Grass (30097)
WY Carbon (56007), Park (56029), Sheridan (56033)*, Sublette (56035)*, Teton (56039)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
10 Madison (10020007)+, Gallatin (10020008)+, Yellowstone Headwaters (10070001)+, Upper Yellowstone (10070002)+, Stillwater (10070005)+, Clarks Fork Yellowstone (10070006)+, Greybull (10080009)+*, North Fork Shoshone (10080012)+, Upper Tongue (10090101)+*, Medicine Bow (10180004)+*, Little Medicine Bow (10180005)+*
14 Upper Green (14040101)+*, Great Divide closed basin (14040200)+
17 Lower Flathead (17010212)+, Snake headwaters (17040101)+, Gros Ventre (17040102)+, Greys-Hobock (17040103)+, Upper Henrys (17040202)+, Lower Henrys (17040203)+, Teton (17040204)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
Basic Description: A large ungulate (bison, or "buffalo").
Reproduction Comments: Most cows breed at 2-4 years; males usually mature at 3 years, but most breeding done by older (6+ years) males. Most mating July-August. Gestation lasts about 9.5 months. Normally 1 calf, is born mainly mid-April to early June (as early as March in Oklahoma, sometimes as late as summer or early fall in South Dakota). Most calves are weaned by late fall or end of first year, remain with mother until spring or later if she does not conceive. Life span 18-22 years.
Ecology Comments: Gregarious. Often forms herds of 11 - 12 animals. Cows and young remain in herds throughout the year. Bulls solitary or in small groups until summer when they begin to mix with cow-calf herds. Home range in Northwest Territories averaged several hundred sq km (Larter and Gates 1990). May live up to about 20 years.
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: Y
Mobility and Migration Comments: Previously made mass migrations across prairie in spring and fall. Probably moved southward a few hundred miles to winter pastures. Mountain popualtions moved to lower elevations in valleys. Movements of U.S. populations now are restricted to parks and vicinity.
Palustrine Habitat(s): HERBACEOUS WETLAND
Terrestrial Habitat(s): Grassland/herbaceous, Savanna, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Habitat Comments: Open plains and grasslands in south; woodland and openings in boreal forest, meadows, and river valleys in north. Like other large grazers, attracted to burned areas the next growing season (Shaw and Carter 1990). During the growing season at the Konza Prairie in northeastern Kansas, preferred areas that had been burned in spring; summer grazing was concentrated in large watershed area (79-119 ha) dominated by warm-season, perennial C4 grasses; in fall and winter, grazed both burned and unburned watersheds more uniformly but grazed most intensively in areas with large stands of cool-season, C3 grasses (Vinton et al. 1993). Cows usually give birth in isolation where vegetation provides cover; isolation during birth is infrequent where cover is lacking (Meagher 1986).
Adult Food Habits: Herbivore
Immature Food Habits: Herbivore
Food Comments: Primarily a grazer. Feeds on grasses, forbs, and sedges. See GHABCOM.
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Phenology Comments: Primarily diurnal (especially early morning and late afternoon), with several grazing periods interspersed with loafing and ruminating (Meagher 1986).
Length: 380 centimeters
Weight: 907000 grams
Economic Attributes
Economic Comments: Has been crossbred with domestic cattle to produce animal ("beefalo") that yields meat at lower cost (Mason 1975). Of medical interest because of apparent nonsusceptibility to cancer (Myers 1983).
Management Summary
Management Requirements: See Meagher (1989) for information on management of Yellowstone bison that leave the park (public hunting outside the park regarded as most feasible management option); management there remains controversial; ranchers fear spread of brucellosis from bison to cattle. (Brucellosis is a coccobacillus that causes a high rate of abortion during the first pregnancy following infection.) See Peterson et al. (1991) for a simulation of alternative bison-brucellosis management strategies for Grand Teton National Park; simulations predict that, after 20 years under any of the proposed management schemes, the proportion of the herd seropositive for BRUCELLA could be reduced from 69% (current level) to, at best, 20%.

See Geist (1990) for vigorous criticism of plan by Agriculture Canada to kill some 3200 so-called "hybrid" bison in Wood Buffalo National Park and replace them with "wood bison," the latter regarded as genetically impoverished and taxonomically insignificant.

Biological Research Needs: Genetics of populations, taxonomic studies of 2 subspecies, comparisons between populations.
Population/Occurrence Delineation
Use Class: Not applicable
Minimum Criteria for an Occurrence: Evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes reliable observation and documentation of one or more individuals in appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Fences.
Alternate Separation Procedure: Occurrence separations should be based on populations that exhibit specific migration patterns, or on appropriate resource agency management units, rather than on specific prescribed distances.
Separation Justification: Almost all populations now enclosed by fences. Exceptional instances in the northern parts of the range (e.g., the free-ranging population along the eastern slope of the northern Rockies in British Columbia).
Date: 23Sep2004
Author: Hammerson, G., and S. Cannings
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
NatureServe Conservation Status Factors Edition Date: 26May1995
NatureServe Conservation Status Factors Author: Meager, M., C. Sahley, and G. Hammerson. Minor revisions J. D. Reichel.
Element Ecology & Life History Edition Date: 31Jan1994
Element Ecology & Life History Author(s): Hammerson, G.

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