BC Conservation Data Centre: Conservation Status Report
Bos bison athabascae
Wood Bison
| Scientific Name: | Bos bison athabascae |
|---|---|
| Scientific Name Synonyms: |
Bison bison athabascae
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| English Name: | Wood Bison |
| Provincial Status Summary | |
| Status: | S2 |
| Date Status Assigned: | May 28, 2010 |
| Date Last Reviewed: | April 16, 2024 |
| Reasons: | Four small herds occupy isolated areas of northeastern British Columbia with range expansion mainly limited by agricultural development. Potential threats include disease transmission and genetic contamination that may result from contact with Plains or commercial bison. Collision with traffic along roads continues to be a source of mortality. |
| Range | |
| Range Extent: | F = 20,000-200,000 square km |
| Range Extent Estimate (km2): | 88,845 |
| Range Extent Comments: | Historically, Wood Bison ranged throughout northeastern British Columbia. Considered extirpated in British Columbia by 1906 (McTaggart-Cowan and Guiget 1965), all current herds are the result of reintroductions. At present, the athabascae subspecies is restricted to four small areas in northeastern BC. They are 1 - the Nordquist herd, reintroduced to Nordquist Flats in the Liard River valley east of Fireside as far as Aline Lake; this herd occasionally strays into the Yukon. 2 - the Nahanni Butte herd which was reintroduced in the Northwest Territories; this herd has expanded their range into British Columbia along the Liard River. 3 - the Etthitun Lake herd is a separate herd reintroduced into the Etthithun Lake area; this herd has expanded and now occurs in BC and Alberta (Alberta Environment and Parks and Alberta Conservation Association 2017). 4 - the Hay-Zama herd which was reintroduced into northwestern Alberta and occasionally crosses the border into British Columbia. A sighting of a bull, 2 cows and a calf in 2012 east of Swift River reported in iNaturalist (https://www.inaturalist.org/observations/4336009) may represent animals straying west from the Nordquist herd as some of that population were fitted with orange ear tags. That record was not included in the calculation of range extent as the animals are not routinely seen that far west (Lewis, C. pers. comm. 2023). The total range extent is approximately 88,845 square km. |
| Area of Occupancy (km2): | E = 26-125 |
| Area of Occupancy Comments: | There have been no detailed assessments of the area of occupancy within the range of Wood Bison in British Columbia. A rough estimate would be that less than 10% of the range is potential habitat. If the Hay-Zama herd is excluded, Wood Bison occupy approximately 45 2x2 km grid cells (D. Fraser, pers. comm. 2023). |
| 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: | There are likely 450-900 animals of which 369-738 are estimated to be mature using the percent mature animals documented in Lewis and Das Gupta (2021). During roadside surveys of the Nordquist herd in winter 2008/2009, the highest count in a single survey was 117 (nine of which were calves). This should be considered a minimum number, as greater numbers of individual age/sex cohorts were counted during previous and subsequent surveys (Thiessen 2009). During an aerial survey of the Etthithun herd in March 2009,156 bison were counted, though 40 of these were in Alberta (Thiessen 2009). That herd had 194 bison seen during the 2021 winter aerial surveys (Lewis and Das Gupta 2022). Even though the Nahanni herd was estimated at 399 non-calf bison in 2004 (Larter et al. 2007), only about 30 of these animals winter in British Columbia. A portion of Alberta's Hay-Zama herd only occasionally wanders into British Columbia. |
| 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). |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | Although Wood 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. (2023), Harper, W. and A. Teucher (2010) |
| Date: | November 30, 2023 |
| References | |
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Alberta Environment and Parks and Alberta Conservation Association. 2017. Status of American Bison in Alberta: Update 2017. Alberta Wildlife Status Report No. 38 (Update 2017). Edmonton AB. 134 pp.
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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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Bork, A.M., C.M. Strobeck, F.C. Yeh, R.J. Hudson, and R.K. Salmon. 1991. Genetic Relationship of wood and Plains bison based on restriction length polymorphisms. Can. J. Zool. 69(1):43-48.
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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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Gates, C.C. et al. 2001. National Recovery Plan for the Wood Bison (Bison bison athabascae). Recovery of Natl. Endangered Wildl. Comm. Rep. No. 21. Ottawa. 50pp.
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Geist, V. 1990. Agriculture versus bison in Canada's Wood Buffalo National Park. Conservation Biology 4:345-346.
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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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Joly, D.O., and Messier, F. 2004. Factors affecting apparent prevalence of turberculosis and brucellosis in wood bison. Journal of Animal Ecology 72:623-631.
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Larter, N.C., D.G. Allaire, and T.S. Jung. 2007. Population survey of the Nahanni Wood Bison population March 2004. Manuscript Report No. 176, Department of Environment and Natural Resources, Government of the Northwest Territories, Fort Simpson, NT. 22p.
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McFarlane, K., G.A. Wilson, and J.S. Nishi. 2006. Management strategies for the conservation of genetic diversity in wood bison. File Report No. 135, University of Alberta. Edmonton, AB.
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Mitchell, J.A. and C.C. Gates. 2002. Status of the Wood Bison (Bison bison athabascae) in Alberta. Alberta Sustainable Resource Development, Fish and Wildlife Division, and Alberta Conservation Association, Wildlife Status Report No. 39, Edmonton, AB. 32 pp.
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Nishi, J.S., C. Stephan, and B.T. Elkin. 2002b. Implications of agricultural and wildlife policy on management and eradication of bovine tuberculosis and brucellosis in free-ranging wood bison of northern Canada. Annals of the New York Academy of Sciences 696:236-244.
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Rowe, M.R. 2006. Halfway/Sikanni Plains Bison inventory. Environmental Stewardship Division, BC Ministry of Environment, Fort St. John, BC. 14pp.
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Rowe, M.R. 2007. Nordquist wood bison inventory. Peace Region Technical Report, Ministry of Environment, Fish and Wildlife Section, Fort St. John, BC. 9pp.
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Wilson, G.A. et al. 2005. Effects of a recent founding event and intrinsic population dynamics on genetic diversity in an ungulate population. Conservation Genetics 6:905-916.
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Wilson, G.A., and C. Strobeck. 1999. Genetic variation within and relatedness among wood and plains bison populations. Genome 42:438-496.
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Wood Bison Recovery Team, (WBRT). 1987. Status report on the Wood bison (Bison bison athabascae) in Canada. 86pp.
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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. 2023. Conservation Status Report: Bos bison athabascae. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jul 8, 2025).