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BC Conservation Data Centre: Conservation Status Report

Ovis canadensis
Bighorn Sheep



 
Scientific Name: Ovis canadensis
English Name: Bighorn Sheep
   
Provincial Status Summary
Status: S3?
Date Status Assigned: April 27, 2015
Date Last Reviewed: February 15, 2015
Reasons: Although the population is stable overall, there have been local, substantial declines in the past, though the most recent ones have shown good signs of recovery in the past decade. Has lost and continues to lose good quality habitat (especially winter range) to various types of land conversion and to forest encroachment, and is vulnerable to stress and stress-related diseases. Domestic sheep can introduce serious illnesses to otherwise healthy herds. The question mark reflects some of the uncertainty found when assigning values to the criteria.
 
Range
Range Extent: G = 200,000-2,500,000 square km
Range Extent Comments: Distributed discontinuously in the Rocky Mountains from the Narraway and Kakwa drainages south to Golden, then continuously south through the Rockies to the U.S. border; and from the Chilcotin Plateau (north of Anahim Lake) south discontinuously through the Fraser, Thompson, and Okanagan drainages to the U.S. border. Introduced populations exist west of Spences Bridge, near Squilax, south of the South Thompson River, and near Grand Forks (Demarchi et al. 2000a, 2000b; Shackleton 1997). Calculated Range Extent is approximately 220,000 sq km.
Area of Occupancy (km2): H = 2,501-12,500
Area of Occupancy Comments: Approximately 5100 2x2 km grid cells are occupied.
 
Occurrences & Population
Number of Occurrences: C = 21 - 80
Comments: There are 59 herds recognized (Harper 1992; Shackleton et al. 1999), within 24 subpopulations; 10 of the "California" form and 14 of the "Rocky Mountain" form (Demarchi 2002). Of these 24 subpopulations, 9 have fewer than 125 individuals (Demarchi 2002), which is considered to be the minimum viable population size for this species (Berger 1990).
Number of Occurrences with Good Viability / Ecological Integrity: Rank Factor not assessed
Number of Occurrences Appropriately Protected & Managed: BC = 1 - 12
Comments: A number of herds range within parks; however, most of these parks protect only a portion of the range of a herd. Protected in Kootenay National Park (half the summer, half the winter, and all of the transitional ranges of the Radium-Stoddart Creek band), Yoho National Park (all the summer range for the Golden herd), Mount Assiniboine Provincial Park (with Banff National Park protects the entire range of the Assiniboine herd), Height of the Rockies Provincial Park (entire range of Quarrie and Bingay Creek herds), Akamina-Kishinena Provincial Park (summer range for the Waterton herd), Kakwa Provincial Park (summer range of the Kakwa herd), Syringa Creek Provincial Park, Cathedral Provincial Park and Snowy Mountain Provincial Park (most of the range of the Ashnola herd), Lac du Bois Grasslands Provincial Park (peripheral winter range of the Kamloops Lake herd), Marble Range and Edge Hills Provincial Parks (limestone summer and witner range of the East Fraser River herd), Big Creek/South Chilcotin (the entire range of the Park Elbo/Relay herd), Junction Sheep Range Provincial Park (all of the range of the Junction herd), and Churn Creek Provincial Park (winter range of the Churn Creek herd; Demarchi 2002).

A complex assemblage of protected areas around Vaseux Lake protects most of the key ranges for the Vaseux herd. The East Columbia Lake Wildlife Management Area and the Wildlife Program property on Mount Broadwood protect important winter ranges. Private land acquisition programs have also secured habitat at Sheep Mountain, Bull River, and along the east side of Columbia Lake (Demarchi 2002).
Population Size: E = 2,500 - 10,000 individuals
Comments: In 2008, Provincial Wildlife Biologists estimated there to be between 5300 and 6600 bighorn sheep in BC.
 
Threats (to population, occurrences, or area affected)
Degree of Threat: B = High
Comments: Generation time: 6-7 years.

Primary threats are habitat loss, degradation and fragmentation; livestock ranching (through disease transmission, range depletion and resource competition); and harassment by the public (Demarchi 2002; Demarchi et al. 2000a, 2000b; A. Fontana, pers. comm.; F. Harper, pers. comm.).

Overharvesting was a threat historically, but provincial wildlife management and conservation efforts have controlled this (Ministry of Environment, Lands and Parks 1996). Small herds, particularly isolated ones, are most vulnerable. There is additional concern about the artificial selection by trophy hunting for rams with smaller horns, but the implications of this are not known (Coltman et al. 2003, Hengeveld et. al. 2010)

Demarchi et al. (2000a, 2000b) state that the greatest threat to bighorns is habitat alienation, whether it is by residential or urban developments, transportation corridor development, mining, dams, agricultural development (including livestock grazing on private land), golf courses, ski hills, etc. Bighorns were displaced many years ago from much of their lowland range in the Okanagan Valley (Demarchi et al. 2000b). The townsites of Radium, Fairmont Hot Springs, and Elko were built on traditional sheep range (Demarchi et al. 2000a). Davidson (1991) calculated that 25 per cent of the traditional winter and spring habitat of bighorn range bordering the Rocky Mountain Trench was alienated and/or developed in the previous 50 years. Open-pit mining and even mine exploration can destroy or alter habitat (Demarchi and Demarchi 1987). About 25 per cent of the winter range in the upper Columbia area has been alienated since the 1940s, and residential development between Fairmont Hot Springs and Brisco have the potential to disrupt north-south migration of bighorn sheep along the western edge of the Rocky Mountains (Davidson 1992, cited by Demarchi et al. 2000a). Transportation corridors such as Highway 97 at Vaseux Lake destroy habitat, interfere with migration routes and carry high speed vehicles that can directly kill bighorns. Irrigated agricultural fields can increase the infection rate of lungworm (Harper 1995; P. Dielman, and H. Schwantje, pers. comm., cited by Demarchi 2002).

Noxious weed invasion (e.g. cheat grass, knapweed) reduces or eliminates nutritious forage with inedible or non-nutritious plants (Demarchi 2002).

Livestock ranching can be a major threat, affecting herds in a number of ways. Domestic sheep commonly carry bacteria such as Pasteurella sp., and can transmit them directly to bighorns, potentially causing fatal pneumonia in otherwise healthy individuals (Foreyt and Jessup 1982; Harper 2001). Although this remains a real threat, there is ongoing work to remove domestic sheep from Bighorn range in order to reduce the exposure (G. Kuzyk pers. comm. 2010). Cattle grazing can also reduce the available food on key winter and spring ranges. In 1987 the Ministry of Forests and Lands estimated that Crown range supported 200,000 cow/calf pairs and yearlings (Demarchi and Demarchi 1987).

Intensive fire suppression over the past 70 or so years has resulted in forest encroachment on grasslands (Davidson 1991; A. Fontana pers. comm.; F. Harper pers. comm.), which has eliminated much grassland habitat, and may be a key factor in the disappearance of some small herds, such as the one at Shorts Creek in the north Okanagan (T. Ethier, pers. comm.). Forest encroachment has reduced critical winter range throughout the Rocky Mountain form's range in British Columbia by up to 50 per cent over the last 70 years, and has had an even greater impact on the mo
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: F = Decline of 10-30%
Comments: This trend is evaluated over the past 18 years, equivalent to 3 generations of Bighorn Sheep (generation time = 6 years; Coltman et al. 2003). In the early 1990's the provincial population of bighorn sheep was likely ~7000-7500 animals, and according to 2008 Ministry of Environment estimates the population is ~5300-6600; this suggests a decline of between 6% and 30%.

In the late 1990's and early 2000's, there were large declines due to a large die-off in the Okanagan and Ashnola, and low lamb survival in the Fraser Basin (BC MInistry of Water, Land, and Air Protection 2004). These populations are now largely increasing (Okanagan) or stable (Thompson). The population in the Cariboo region appears to be showing moderate declines (BC Ministry of Environment 2008).
Long-Term Trend: DE = Decline of 30-70%
Comments: There are no good estimates of population sizes of Bighorn sheep prior to European settlement, but numbers drastically declined in the last half of the 1800s due to excessive hunting, disease, competition from livestock, and restriction of winter range (Demarchi et al. 2000a, b). It is estimated that in 1900 there were approximately 1775-3400 "Rocky Mountain" bighorns in both Alberta and BC (with the majority being in Alberta, and only 1350 "California" bighorns in BC (Demarchi et al. 2000a, b). They have since recovered to the current provincial population of 5300-6600 (BC Ministry of Environment 2008), however this is likely much smaller than the historical population prior to the large declines of the late 19th century.

Although there are no reliable estimates of historical abundance, the suitable habitat at present is likely <50% of the capable habitat within the historic distribution because of forest access roads, forest succession, competition with livestock, and human disturbance (BC Ministry of Water, Land, and Air Protection 2004).

Bighorn sheep populations, particularly those in the Rocky Mountain population, exhibit extreme periodic (approximately every 20-25 years) fluctuations. These severe die-offs are thought to be a natural phenomenon that occur when populations exceed their carrying capacity, though it is likely that the mortality rates that typify these die-offs are now higher due to the introduction of exotic diseases and human-caused reductions in habitat (Demarchi et al. 2000a).
 
Other Factors
Intrinsic Vulnerability: Rank Factor not assessed
Environmental Specificity: BC=Narrow to moderate.
Comments: Bighorn sheep are dependent upon adequate escape terrain, lambing sites, winter range, mineral licks, and sufficient quantity and quality of forage.
Other Rank Considerations:
 
Information Gaps
Research Needs:
Inventory Needs: Systematic surveys must be completed every 3 to 5 years to be able to adequately monitor bighorns (I. Hatter, pers. comm.).
 
Stewardship
Protection: Specific sites that are critical to the survival of a herd should be protected where landscape prescriptions are insufficient: e.g. early spring range, lambing areas, late fall rutting areas, watering holes, movement corridors, resting areas, and security sites (Demarchi 2002). These sites may be protected as Wildlife Habitat Areas under the Forest Practices Code Act.
Management: Maintain adjustable harvest regulations according to inventories (F. Harper, pers. comm.). The following is adapted from the account in the Identified Wildlife Management Strategy (Demarchi 2002):

Reduce or, if possible, eliminate contact with other livestock, especially domestic sheep and goats.

Minimize disturbance during critical times in critical habitats.

Maintain bighorn access to movement corridors and critical ranges.

Maintain and enhance or restore appropriate forage species and seral stages of forests and grasslands in a condition suitable to bighorns. For example, maintain at least 50 per cent of each winter range in late seral/climax condition bunchgrass-dominated communities with abundant, tall grass. Prevent the introduction of noxious weeds and control their spread. Re-vegetation of disturbed sites should be done using native species mixes.
 
Version
Author: Nagorsen, D. and L. Ramsay (Cannings, S.; Teucher, A)
Date: March 02, 2015
 
References
B.C. Ministry of Water, Land and Air Protection. 2004. Bighorn Sheep (Ovis canadensis) in Accounts and Measures for Managing Identified Wildlife - Accounts V. 2004. B.C. Ministry of Water, Land and Air Protection, Victoria, B.C. Available: http://www.env.gov.bc.ca/wld/frpa/iwms/accounts.html (accessed May 18, 2010).
Blower, D. 1988. Wildlife distribution mapping, big game series, mountain sheep. Unpubl. map by B.C. Minist. Environ., Lands and Parks, Victoria, BC.
Coltman, D.W., P. Donoghue, J.T. Jorgenson, J.T. Hogg, C. Strobeck and M. Festa-Bianchet. 2003. Undesireable evoloutionary consequenses of trophy hunting. Nature 426: 655-658.
Davidson, P. W. 1991. East Kootenay Bighorn Sheep enhancement project: completion report. Unpublished report, British Columbia Wildlife Branch, Ministry of Environment, Cranbrook, B.C. 183pp.
Demarchi, D. A., and R. A. Demarchi. 1987. Wildlife habitat--the impacts of settlement. in A. Murray, editor. Our Wildlife Heritage: 100 years of wildlife management. Centennial Wildlife Society of B.C. Victoria, B.C. 192pp.
Demarchi, M.W., and D.A. Demarchi. 1994. Rocky Mountain Bighorn Sheep in the Kootenay Region. A habitat and population enhancement plan to 2004. Rep. prepared for B.C. Minist. Environ., Lands and Parks. 91pp.
Demarchi, R. A. 2002. Bighorn Sheep, Ovis canadensis. Pages 433-454 in K. Paige (technical editor), Standards for managing identified wildlife, Version 2. Draft for technical review. Ministry of Water, Land and Air Protection, Biodiversity Branch, Victoria, BC. 492pp.
Demarchi, R.A., C.L. Hartwig, and D.A. Demarchi. 2000a. Status of the Rocky Mountain Bighorn Sheep in British Columbia. B.C. Ministry of Environment, Lands and Parks, Victoria, B.C. Wildlife Branch Bulletin. B-99. 60 pp.
Demarchi, R.A., C.L. Hartwig, and D.A. Demarchi. 2000b. Status of the California Bighorn Sheep in British Columbia. B.C. Ministry of Environment, Lands and Parks, Victoria, B.C. Wildlife Branch Bulletin B-98. 60pp.
Foreyt, W.J. and D.A. Jessup. 1982. Fatal pneumonia of Bighorn Sheep following association with domestic sheep. Journal of Wildlife Diseases 18:163-168.
Harper, F. 1992. California bighorn sheep in British Columbia. Unpubl. rep. B.C. Minist. Environ., Lands and Parks, Kamloops, B.C. 6pp.
Harper, W. L. 2001. Workshop for the recovery of Bighorn Sheep in the South Okanagan. Ministry of Environment, Lands and Parks. Penticton, B.C. 34pp.
Harrison, S., and D. M. Hebert. 1988. Selective predation by cougar within the Junction Wildlife Management Area. Proceedings of the Biennial Symposium of Northern Wild Sheep and Goat Council 6:292-306.
Hebert, D. M., and S. Harrison. 1988. The impact of coyote predation on lamb mortality patterns at the Junction Wildlife Management Area. Proceedings of the Biennial Symposium of the Northern Wild Sheep and Goat Council 5:283-291.
Ministry of Environment, Lands and Parks. 1996. Wildlife harvest strategy - Improving British Columbia's wildlife harvest regulating. Victoria, BC. 73pp.
Shackleton, D.M., ed. 1997. Wild sheep and goats and their relatives. IUCN, Gland, Switzerland. (Available from IUCN Publ. Serv. Unit, Cambridge CB2 0DL, U.K.). 390pp.
Shackleton, D.M., I. Hatter, and H. Schwantje. 1999. Rocky Mountain Sheep in British Columbia in Geist, V. Return of Royalty: Wild Sheep of North America. Boone and Crockett Club and Foundation for North American Wild Sheep. In press.
Toweill, D. and V. Geist. 1999. Return of royalty. Unpublished report, Boone and Crockett Club. Missoula, MT.
 

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Suggested Citation:

B.C. Conservation Data Centre. 2015. Conservation Status Report: Ovis canadensis. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jan 24, 2022).