BC Conservation Data Centre: Conservation Status Report
Bos bison
American Bison
| Scientific Name: | Bos bison |
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| Scientific Name Synonyms: |
Bison bison
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| English Name: | American Bison |
| Provincial Status Summary | |
| Status: | S2 |
| Date Status Assigned: | April 16, 2024 |
| Date Last Reviewed: | April 16, 2024 |
| Reasons: | Four small herds of the reintroduced Wood Bison occupy isolated areas of northeastern British Columbia with range expansion mainly limited by agricultural development. Potential threats include disease transmission and collision with traffic along roads continues to be a source of mortality. The Plains Bison subspecies is extirpated from its historical range in the province although an escaped population exists on Pink Mountain. |
| Range | |
| Range Extent: | F = 20,000-200,000 square km |
| Range Extent Estimate (km2): | 88,845 |
| Range Extent Comments: | The athabascae subspecies was extirpated in British Columbia by 906 (McTaggart-Cowan and Guiget 1965) and current herds are the result of reintroductions. The subspecies is restricted to four small areas in northeastern BC. The bison subspecies was extirpated at an even earlier date. It was later accidentally introduced into the Pink Mountain area, well outside the historical range of that subspecies and is considered an introduced species there; it is not considered in the range extent of the species. |
| Area of Occupancy (km2): | E = 26-125 |
| Area of Occupancy Comments: | If the Hay-Zama herd is excluded, Wood Bison occupy approximately 45 2x2 km grid cells (D. Fraser, pers. comm. 2023). Plains Bison are extirpated in the subspecies historical range and the introduction in the Pink Mountain area is excluded from the estimate of the area of occupancy. |
| Occurrences & Population | |
| Number of Occurrences: | Rank Factor not assessed |
| Comments: | The Element Occurrence concept for mammals with large home ranges does not always best represent the rarity category when calculating the status rank using NatureServe methods. In the case of Wood Bison, population size will be factored within the rarity category, which will contribute to the overall status rank. |
| Number of Occurrences with Good Viability / Ecological Integrity: | Rank Factor not assessed |
| Percent Area with Good Viability / Ecological Integrity: | E = Good (21-40%) |
| Comments: | The Nahanni herd is likely the most viable of all the populations in British Columbia since it is most isolated from both disease and potential mixing with Plains Bison. It is also the population that appears to be growing the fastest. The other introduced populations are still quite small and have low levels of genetic diversity. The Etthithun Lake and Hay-Zama herds are at greater risk of contacting commercial bison than the Nordquist and Nahanni herds. Growing numbers and expanding range in the Yukon may mean that the species could spread into northwestern BC from the reintroduced population there. |
| Number of Occurrences Appropriately Protected & Managed: | A = None |
| Comments: | Small portions of the habitat of the Nordquist herd are protected by portions of the Portage Brule Rapids Ecological Reserve and Protected Area and the Liard River Cooridor Park. |
| Population Size: | C = 250 - 1,000 individuals |
| Comments: | The 2022 population estimate (B.C. Ministry of Water, Land and Resource Stewardship 2022) indicates between 800 and 1900 individuals, although this includes both Wood Bison and the introduced Plains Bison populations. There are likely 450-900 Wood Bison of which 369-738 are estimated to be mature using the percent mature animals documented in Lewis and Das Gupta (2021). Since Plains Bison are an introduced outside the historical range of the subspecies it is not included in the estimate of the population size in this assessment. |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | A = Very high |
| Comments: | A formal threats assessment for Canada was completed by COSEWIC (2013). Bison infected with tuberculosis and brucellosis in and around Wood Bison National Park (WBNP) threaten the health and potential of reintroduced of Wood Bison in northern Alberta, northern British Columbia, and southwest Northwest Territories (Gates et al. 2001). In WBNP, where 49% of Wood Bison were seropositive for tuberculosis and 31% were seropositive for brucellosis (Joly and Messier 2004), populations had declined 80% since 1971 to approximately 2900 animals (Mitchell and Gates 2002). The two herds most at risk of contact with diseased bison from WBNP are the Nahanni and Hay-Zama herds, because of their proximity to infected bison, and the habit of dispersing male bison to travel long distances. Hopefully, interim "bison-free" buffer zones established by Alberta and the Northwest Territories will help prevent spread of these diseases to bison in British Columbia. Cross-breeding with Plains bison or commercial bison is another significant threat, the mostly likely source being escaped commercial bison. The Pink Mountain population of Plains Bison is also potential source of cross-breeding. This Plains Bison herd was estimated at 1302 animals in 2006 (Rowe 2007), however, this population has likely declined (C. Lewis pers. comm. 2023) and the policy of restricting each subspecies to mutually exclusive ranges to prevent hybridization (Harper et al. 2000) means this is less likely to occur. Loss of genetic diversity is also a significant threat facing wood bison in British Columbia. All the reintroduced wood bison in British Columbia are direct descendants of the 21 animals captured in 1965 near Needle Lake in the Nyarling River area of WBNP and relocated to Elk Island National Park (EINP) (Harper et al. 2000). This was the first genetic bottleneck. For the Nordquist population, the second genetic bottleneck occurred in 1995 when 49 animals were translocated from ElNP to establish this population in the Liard River valley. Due to this series of founding events and population bottlenecks, genetic diversity is not well distributed among disease-free Wood bison herds in Canada (McFarlane et al. 2006). Among non-diseased, free-roaming populations of Wood bison, the Nordquist herd has the lowest current level of heterozygosity, and the poorest projected trend over the next 200 years, based on simulated population viability analysis (McFarlane et al. 2006). Further loss of genetic diversity in Wood Bison populations is probable due to genetic drift in British Columbia's small populations, particularly if only a few males are responsible for the majority of offspring born to a population (Wilson et al. 2005). The smallest herds (e.g. Nordquist and Etthithun), have the lowest heterozygosity. Movement of animals among all herds will significantly reduce the rate at which diversity is lost (McFarlane et al. 2006). To a lesser extent, collisions with vehicles are a threat to the Nordquist and Etthithun herds. Wolf predation may limit population growth rates in some areas. |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | I = Increase of >25% |
| Comments: | Generation time for Wood Bison is estimated at 8 years (COSEWIC 2013) therefore the 3 generation time for short-term trend is 24 years. The 1999 population estimate was about 45 animals (Harper and Gates 2000) and the 2022 estimate was about 450 to 900 animals (B.C. Ministry of Water, Land and Resource Stewardship 2022). This is a 900-1900% increase. |
| Long-Term Trend: | A = Decline of >90% |
| Comments: | COSEWIC (2013) and ECCC (2018d) summarize the historic extent and large scale decline of Wood Bison in Canada, including British Columbia. Wood Bison once occurred over a large part of northeastern British Columbia, although they were unevenly distributed and never as numerous as Plains Bison. Fossil specimens have been found in northern British Columbia from Atlin, Cecil Lake, and the Fort Saint John areas (McTaggart-Cowan and Guiget 1965). Wood Bison were nearly eliminated by uncontrolled hunting for the fur trade during the late 1800's and the last confirmed Wood Bison from the primordial population was shot near Fort St. John in 1906 (COSEWIC 2013, McTaggart-Cowan and Guiget 1965). Plains Bison is extirpated from its historical range in British Columbia. |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | Although bison are capable of fairly rapid population growth rates in the absence of significant threats, the intrinsic lack of genetic diversity within the relatively small British Columbia populations means they are still vulnerable further loss of heterozygosity through genetic drift. |
| Environmental Specificity: | C=Moderate. Generalist or community with some key requirements scarce. |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | Monitor the disease status of free-roaming and domestic bison (Harper et al. 2000). The majority of genetic diversity still exists in the diseased wood bison populations of WBNP (Wilson and Strobeck 1999, Wilson et al. 2005), since the genetic diversity of the salvaged disease-free bison is substantially less due to founder effects and genetic drift (McFarlane et al. 2006). Further research into ways to salvage disease-free wood bison from WBNP are needed. A recent effort to establish a second captive-breeding population at Hook Lake began in 1996 (Nishi et al. 2002b). Unfortunately, after 10 years of effort, the Hook Lake Wood Bison Recovery Project was terminated in March 2006, and the 120 animals in the herd were destroyed after tuberculosis was detected in one of the founder animals and several captive born bison. |
| Inventory Needs: | Routine inventories of populations are needed to monitor changes in population distribution, size, and demographics (Harper et al. 2000). |
| Stewardship | |
| Protection: | |
| Management: | |
| Version | |
| Author: | Fraser, D.F. |
| Date: | March 12, 2024 |
| References | |
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B.C. Ministry of Water, Land and Resource Stewardship. 2022. Large ungulate abundance in British Columbia. Online. Available: https://www2.gov.bc.ca/assets/gov/environment/plants-animals-and-ecosystems/wildlife-wildlife-habitat/ungulates/2022_provincial_ungulate_population_estimates.pdf (accessed 16 April 2024).
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COSEWIC. 2013. COSEWIC assessment and status report on the Plains Bison Bison bison bison and the Wood Bison Bison bison athabascae in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xv + 109 pp.
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Cowan, I.M. and C.J. Guiguet. 1965. The mammals of British Columbia. Handb. No. 11, B.C. Prov. Mus., Victoria. 414pp.
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Environment and Climate Change Canada. 2018d. Recovery Strategy for the Wood Bison (Bison bison athabascae) in Canada. Species at Risk Act Recovery Strategy Series. Environment and Climate Change Canada. Ottawa. viii + 59 pp.
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Harper, W.L., J.P. Elliot, I. Hatter and H. Schwantje. 2000. Management plan for Wood Bison in British Columbia. Ministry of Environment, Lands and Parks Wildlife Branch, Victoria, B.C. Wildlife Bulletin No. B-102. 43pp.
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Lewis, C. J. and S. Das Gupta. 2021. Wood Bison - Etthithun Herd Minimum Population Survey Results: February 22-25th, 2021. Technical Report. British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Peace Region, BC. 30 pp.
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Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.
Suggested Citation:
B.C. Conservation Data Centre. 2024. Conservation Status Report: Bos bison. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed May 21, 2026).