Bison bison


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Bison bison
Species Authority: (Linnaeus, 1758)
Common Name(s):
English American Bison
Taxonomic Notes: There are two recognized subspecies in North America: Bison bison bison and B. b. athabascae.

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Gates, C. & Aune, K.
Reviewer(s): Gates, C. (Bison Red List Authority) & Schipper, J. (Global Mammal Assessment Team)
This species is listed as Near Threatened in light of its dependence on an ongoing conservation programme, a very limited number of viable populations (five), and small populations. The North America bison population underwent a drastic decline in 19th century caused by over hunting but has since partially recovered. There has been a modest increases in the number of conservation herds and individuals in populations managed for species conservation and ecological restoration, however, all mature individuals occur within active management programs which is ceased would result in the species qualifying for a threatened status. About 97% of the continental population is managed for private captive commercial propagation; very few of these herds are managed primarily for species conservation and none is managed in the public interest for conservation. Herds managed for conservation purposes in the public interest are typically small (< 400), and populations are widely dispersed with few geographic situations that provide conditions for natural movements between subpopulations. The total number of mature individuals in wild free-ranging and semi-free-ranging populations is estimated to be approximately 11,250 and only 5 subpopulations have more than 1,000 individuals, thus making this species nearly qualify for Vulnerable C2a(i). The species is not currently in decline but wild mature individuals could be greatly reduced if current management regimes are changed. This is a conservation dependant species.

The species is most limited in Mexico, where only one herd occurs in the wild; it is subject to adverse policies when individuals move across the international border into the United States where they are classified as livestock. The current number of ecologically restored large populations managed primarily for conservation (populations exceeding 1,000 and managed in the presence of most natural limiting factors) is small. Creation of opportunities for a few additional, large-scale ecological restoration projects is dependent on cooperation between government agencies and non-government organizations. Future progress in conservation and recovery of the North American bison will depend on significant changes in its legal status and management as wildlife by federal and state/provincial agencies, harmonization of policies and activities among agencies at multiple levels, and cooperation with environmental organizations. Cooperation and coordination are particularly important where different agencies or organizations have separate management jurisdiction for adjacent land areas within an ecosystem unit in which ecological restoration of bison is possible.

Geographic Range [top]

Range Description: Original North American range extended from northern Mexico to Alaska. Plains bison occurred from Northern Mexico to central Alberta. Wood bison occurred from central Alberta to Alaska. Current range is restricted by land use and wildlife management policies in the southern area and by wildlife and reportable disease management policies in the north. Bison in conservation herds currently occupy less than 1% of their original range (Sanderson et al. 2008).
Canada (Alberta, British Columbia, Manitoba, Northwest Territories, Ontario, Saskatchewan); United States (Alabama - Regionally Extinct, Arizona, Arkansas - Regionally Extinct, California, Colorado - Regionally Extinct, Delaware - Regionally Extinct, District of Columbia - Regionally Extinct, Florida - Regionally Extinct, Georgia - Regionally Extinct, Idaho, Illinois - Regionally Extinct, Indiana - Regionally Extinct, Iowa - Regionally Extinct, Kansas - Regionally Extinct, Kentucky - Regionally Extinct, Louisiana - Regionally Extinct, Maryland - Regionally Extinct, Massachusetts - Regionally Extinct, Michigan - Regionally Extinct, Minnesota - Regionally Extinct, Mississippi - Regionally Extinct, Missouri - Regionally Extinct, Montana, Nebraska - Regionally Extinct, Nevada - Regionally Extinct, New Mexico - Regionally Extinct, New York - Regionally Extinct, North Carolina - Regionally Extinct, North Dakota - Regionally Extinct, Ohio - Regionally Extinct, Oklahoma - Regionally Extinct, Oregon - Regionally Extinct, Pennsylvania - Regionally Extinct, South Carolina - Regionally Extinct, South Dakota, Tennessee - Regionally Extinct, Texas - Possibly Extinct, Utah, Virginia - Regionally Extinct, Washington - Regionally Extinct, West Virginia - Regionally Extinct, Wisconsin - Regionally Extinct, Wyoming)
Regionally extinct:
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: There are approximately 19,000 total plains bison in 54 conservation herds (herds managed in the public interest by governments and environmental organizations), and 11,000 total wood bison in 11 conservation herds. The proportion of mature individuals is difficult to calculate as even wild herd are often intentionally managed with skewed sex ratios. An optimistic estimate of the total number mature individuals for both subspecies (breeding adults including subadult males) is 23,000 (75% of total), while a more realistic estimate (breeding females and mature males only) is 21,000 (70% of total). Populations are considered viable in the long term if they exceed 1000 individuals. There are 5 plains bison conservation herds and 3 wood bison conservation herds each exceeding 1000 - therefore the total number of viable populations is only 8.

Six wild (free-ranging, not confined primarily by fencing) herds of plains bison occur in the natural range of this subspecies: two in Canada, three in the United States and one in Mexico. There are ten wild populations of wood bison within the natural range of the sub-species; all are in Canada. Wood bison are extirpated in the wild in Alaska, a natural range state. There are approximately 500,000 bison in captive commercial populations (mostly plains bison) on about 4000 privately owned ranches.

Under the IUCN Red List Guidelines, commercial herds are not eligible for consideration in determining a Red List designation therefore we have calculated the total population of bison in conservation herds to be approximately 30,000 individuals and the mature population to be approximately 20,000 individuals. Of the total number presented only 15,000 total individuals are considered wild bison in the natural range within North America (free-ranging, not confined primarily by fencing). Of the wild populations, only 11,250 (75% see above) are mature individuals using the most conservative estimate.
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: North American bison are primarily grazers and forage primarily in grassland and meadow communities. They had the widest natural range of any North American herbivore, from the arid grasslands of Chihuahua State in northern Mexico, through the grasslands of the Great Plains, to the riparian meadows of interior Alaska. They can persist in arid regions (Mexico and New Mexico) and in areas experiencing deep snow cover (Yellowstone National Park). Grasses and sedges form the mainstay of the annual diet in all regions. However, summer and fall diets may be broader, including flowering plants, woody plant leaves, and lichens, in addition to grasses and sedges, depending on local availability. Bison excavate snow at foraging sites by sweeping it away using side to side motions of their muzzle. The plains bison undertook seasonal migrations when it was abundant prior to European settlement of the continent. It no longer migrates owing to land use change and depopulation. The wood bison was not migratory and remains so. Both subspecies exhibit strong seasonal aggregation during the calving through breeding seasons (May through August).
Systems: Terrestrial

Use and Trade [top]

Use and Trade: Approximately 500,000 bison are commercially propagated on 4000 farms and ranches in North America. Conservation practices vary widely among private owners and are not regulated. Escapes from private commercial herds have been documented in Montana, Alberta, and British Columbia. Artificial selection for market traits is a cause for concern: escaped individuals may become established in the wild or interbreed with established wild populations.

Threats [top]

Major Threat(s): In the 19th Century, market, subsistence and recreational hunting nearly eliminated the bison throughout its range in North America. Conservation measures have brought about limited recovery in the wild and in captive conservation herds. Private commercial production of bison has resulted in significant numerical recovery, but does not provide for conservation of the bison as wildlife in the sense used for Red List designation. Existing threats include: habitat loss; genetic manipulation of commercial bison for market traits; small population effects in most conservation herds; few herds are exposed to a full range of natural limiting factors; cattle gene introgression; loss of genetic non-exchangeability through hybridization between bison subspecies; and the threat of depopulation as a management response to infection of some wild populations hosting reportable cattle diseases. Canada, the United States and Mexico list bison nationally as both wildlife and domestic livestock. Legal status varies among State and Provincial jurisdictions. In Canada, four provinces and two territories list bison as both wildlife and livestock. Bison are listed by 20 states in the United Sates; 10 states list bison as wildlife and all 20 list them as livestock. An additional threat to populations of this species is culling to prevent the spread of bovine tuberculosis and brucellosis.

Conservation Actions [top]

Conservation Actions: A recovery program for wood bison has existed in Canada since the early 1960s where the subspecies was designated as 'Threatened' by the Committee on Endangered Species of Wildlife in Canada (COSEWIC). In May 2004 COSEWIC assessed the status of plains bison and recommended listing them as 'Threatened' in Canada. National Refuges and Parks and State parks play an important role in maintaining conservation herds in Canada and the United States. Wild free-ranging herds are managed by government agencies. The Nature Conservancy manages 8 captive herds and the American Prairie Foundation (World Wildlife Fund) manages one herd primarily for conservation objectives. Restoration of large populations of plains bison are being planned in southern Colorado and northern Montana. The State of Alaska is at an advanced stage in planning to reintroduce wood bison to the wild. There are no coordinated federal initiatives for plains bison conservation in any nation in North American, although there is some discussion of a coordinated strategy by the US Department of the Interior at the time of writing (January 2007).

The Bison Specialist Group (North America) is developing a bison conservation assessment and action plan that will provide support and guidance for policy development and conservation planning and management for public and private sector projects, including: numeric, geographic and genetic status of North American bison, including public and private herds; a review of legislation and policies of individual range states regarding bison conservation; geographic assessment of priority conservation areas in North America (Wildlife Conservation Society lead); enhancing the capacity of members of the Bison Specialist Group and organizations they represent to provide timely, innovative and practical solutions to conservation challenges; guidelines for management in support of species’ conservation and ecological restoration.

There are potential opportunities for ecological restoration of herds managed primarily for conservation on federal, state, provincial lands in some jurisdictions (Sanderson et al. 2008). There may be opportunities for establishing herds on Native-owned lands that are managed for combined conservation and socio-economic purposes. However, there are significant challenges in integrating western science-based conservation into such community-based initiatives.

Bison bison athabascae is listed in CITES Appendix II.

Bibliography [top]

Boyd, D. and Gates, C. C. 2006. A Brief Review of the Status of Plains Bison in North America. Journal of the West 45(2): 15-21.

Boyd, D. P. 2003. Conservation of North American bison: status and recommendations. Faculty of Environmental Design, University of Calgary.

Committee on the Status of Endangered Wildlife in Canada. 2004. Assessment and status report on the plains bison (Bison bison bison) in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa, Canada.

Freese, C. H., Aune, K. E., Boyd, D. P., Derr, J. N., Forrest, J. C., Cormack Gates, C., Gogan, P. J., Grassel, S. M., Halbert, N. D., Kunkel, K. and Redford, K. H. 2007. Second chance for the plains bison. Biological Conservation 136: 175-184.

Gates, C. C., Elkin, B. and Dragon, D. 1995. Investigation, control and epizootiology of anthrax in an isolated, free-roaming bison population in northern Canada. Canadian Journal of Veterinary Research 59: 256-264.

Gates, C. C., Stelfox, B., Muhly, T., Chowns, T. and Hudson, R. J. 2005. The ecology of bison movements and distribution in and beyond Yellowstone National Park: A critical review with implications for winter use and transboundary population management. University of Calgary, Faculty of Environmental Design, Calgary, Alberta, Canada.

Gates, C. C., Stephenson, R. O., Reynolds, H. W., Van Zyll De Jong, C. G., Schwantje, H., Hoefs, M., Nishi, J., Cool, N., Chisholm, J., James, A. and Koonz, B. 2001. National recovery plan for the wood bison (Bison bison athabascae). Recovery of Nationally Endangered Wildlife (RENEW), Ottawa, Ontario, Canada.

Gross, J. E., Wang, G. 2005. Effects of population control strategies on retention of genetic diversity in National Park Service bison (Bison bison) herds. Final Report, Yellowstone Research Group, USGS-BRD. United State Geological Survey, Bozeman, Montana, USA.

Halbert, N. D. and Derr, J. N. 2007. A comprehensive evaluation of cattle introgression into US Federal bison herds. Journal of Heredity 98(1): 1-12.

Komers, P. E., Messier, F. and Gates, C. C. 1994. Plasticity of reproductive behaviour in wood bison bulls: on risks and opportunities.

List, R., Ceballos, G., Curtin, C., Gogan, J. P., Pacheco, J. and Truett, J. 2007. Historic Distribution and Challenges to Bison Recovery in the Northern Chihuahuan Desert. Conservation Biology 21(6): 1487-1494.

Reynolds, H., Gates, C. and Glahoht, R. 2003. Bison. In: J. Chapman and G. Feldhamer (eds), Wild mammals of North America, biology, management, and economics, pp. Pages 1009 - 1060. Johns Hopkins University Press, London, UK.

Reynolds, H. W. and Hawley, A. W. L. 1987. Bison ecology in relation to agricultural development in the Slave River lowlands, NWT. Occasional Paper - Canadian Wildlife Service 63: 74 pp.

Sanderson, E., Redford, K. H., Weber, B., Aune, K., Baldes, D., Berger, J., Carter, D., Curtin, C., Derr, J., Dobrott, S., Fearn, E., Fleener, C., Forrest, S., Gerlach, C., Gates, C. C., Gross, J., Gogan, P., Grassel, S., Hilty, J. A., Jensen, M., Kunkel, K., Lammers, D., List, R., Minkowski, K., Olson, T., Pague, C., Robertson, P. B. and Stephenson, B. 2008. The Ecological Future of the North American Bison: Conceiving Long-term, Large-scale Conservation of Wildlife. Conservation Biology 22(2): 252-266.

Stephenson, R. O., Gerlach, S. C., Gurthrie, R. D., Harington, C. R., Mills, R. O. and Hare, G. 2001. Wood bison in late holocene Alaska and adjacent Canada; paleontological, archaeological and historical records. In: S. C. Gerlach and M. S. Murray (eds), People and wildlife in northern North America: essays in honor of R. Dale Guthrie, pp. 125-159. BAR International Series 944.

Van Zyll de Jong, C. G. 1986. A systematic study of recent bison, with particular consideration of the wood bison. National Museum of Natural Science Publication 6: 69 pp.

van Zyll de Jong, C. G., Gates, C., Reynolds, H. and Olson, W. 1995. Phenotypic variation in remnant populations of North American bison. Journal of Mammalogy 76: 391-405.

Ward, T. J., Skow, L. C., Gallagher, D. S., Schnabel, R. D., Nall, C. A., Kolenda, C. E., Davis, S. K., Taylor, J. F. and Derr, J. N. 2001. Differential introgression of uniparentally inherited markers in bison populations with hybrid ancestries. Animal Genetics 32: 89-91.

Wilson, D.E. and Reeder, D.M. 2005. Mammal Species of the World. Johns Hopkins University Press, Baltimore, MD, USA.

Wilson, G. and Strobeck, C. 1999. Genetic variation within and relatedness among wood and plains bison populations. Genome 42: 483-496.

Citation: Gates, C. & Aune, K. 2008. Bison bison. The IUCN Red List of Threatened Species. Version 2014.2. <>. Downloaded on 01 August 2014.
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