The California bighorn sheep, Ovis canadensis californiana, and Rocky Mountain bighorn sheep, O. c. canadensis are BLUE-listed because their winter ranges are threatened by past overgrazing, competition with domestic stock and other ungulates, land alienation and human encroachment. They are also threatened by disease, particularly those transmitted by domestic sheep.
Wild sheep are predominately grazers, relying on grassland habitats. Grasses, sedges and forbs comprise the majority of bighorn food but up to 25% of the diet may be shrubs such as sage, saskatoon, bearberry, juniper and willow. Breeding occurs in November and usually takes place on high, grassy slopes of the winter range. Ewes give birth to lambs from April-May on rough, rocky escape terrain adjoining the winter range grasslands. Some bighorns are migratory. Ewes and lambs remain on the winter range until late spring and early summer, when the lambs are strong enough to move with the ewes to higher, summer ranges; adult rams usually leave the winter ranges before the ewes and younger sheep. Bighorns are gregarious: ewes, lambs, yearlings and two-year-old rams stay together for much of the year in groups which may reach 100 animals; rams of about three years and older form loose aggregations and, except for the rut, remain apart from the females and younger animals. Bighorns are not territorial. Home ranges vary with the distance between summer and winter ranges, which may be as much as 60 km apart.
California bighorn sheep are scattered in small herds on the mountains and grasslands of the Ashnola River system, the east side of the South Okanagan valley in the vicinity of Vaseux Creek, Shorts Creek west of Okanagan Lake, the Fraser River basin from Lillooet north to Williams Lake, the upper Taseko and Chilko Rivers and an isolated herd on Far Mountain, north of Anaheim Lake. Two herds have been established near Kamloops Lake and Grand Forks following transplants.
Rocky Mountain bighorn sheep are found primarily in the southern Rocky Mountains and Rocky Mountain Trench east of the Columbia River, from the 49th parallel north to the Blaeberry River. Smaller herds are located between the Blaeberry and upper Wapiti Rivers. Transplants have created bands near Salmo, Castlegar, Squilax, Spences Bridge and Adams Lake.
Ecoprovinces: Ecosections
California bighorn
CEI: CCR, CAB, CHP, FRB, WCU
SIM: SFH
SOI: PAR, SCR, SOB, SOH, OKR, NOB, NOH, NTU, STU, THB
Rocky Mountain bighorn
SIM: SCM, FRR, BRR, COC, SFH, CPK, NPK, SPK
SOI: PAR
AT, ESSF, MS, IDF, PP, BG
Many California bighorn herds do not have available alpine habitat and remain in one general location year-round. Some herds in the Ashnola River system spend their summers in subalpine forested areas or open forests below the subalpine, while others move into typical bighorn sheep alpine habitat each summer. Suitable forested areas, such as dense thickets of brush and young conifers or dense stands of spruce, pine or fir frequently provide escape habitat for summering California bighorns.
Most Rocky Mountain bighorn herds forage on alpine and subalpine meadows, grassy mountain slopes, high ridges and in high cirques and basins with readily available steep and rugged rock bluffs, cliffs and ledges for escape; this summer habitat is often between 2000 and 2500 m. Some herds in the Rocky Mountains remain in alpine habitats all year round. The Spences Bridge herd does not have access to any alpine habitats.
Between summer and winter ranges are linkage corridors for bighorn sheep moving between their primary seasonal ranges; transitional ranges usually include open forested habitat.
The limiting habitat for bighorn sheep is winter range. There are two types - normal winter range and severe winter range. In the occasional severe winter, the priority for sheep is relief from the energy drain of pushing through snow. Large canopied trees may provide this relief. In normal winters, the priority for sheep is access to food in areas that provide predator escape terrain. Most herds winter on low-elevation, south- and west-facing slopes where relatively warm temperatures and a lack of persistent snow permit sheep to locate food. These are often below 600 m elevation but range to 1800 m. Some herds winter on high, wind-swept ridges that are both influenced by periodic temperature inversions and regularly cleared of snow by strong winds. South- and west-facing grasslands within ponderosa pine and Douglas-fir forests provide the majority of winter habitat; however, timbered, rocky bluffs and openings with early seral stages following wild fires or logging are also used by foraging sheep. Escape terrain is critical on winter ranges and is usually provided by steep rock bluffs and canyons with narrow ledges, rugged rocky slopes, talus slopes, and dense timber patches bordering the winter foraging sites. The two types of winter range should be close to one another. Without access to severe winter range the consequence may be substantial die-offs.
AB, AC, AG, AM, AU, BS, DF, DL, DP, EF, FP, LP, MS, OV, PP, RO, SD, SG, SM, SS, TA, WP
Stages 4 to 9 (pole/sapling to old forest) are used as cover, both escape and thermal, and as a canopy to reduce the effect of deep or ice crusted snowfalls.
Low-elevation bunchgrass ranges on south- and west-facing slopes, adjacent to suitable escape terrain and water, provide winter habitat for all age classes and spring lambing areas. A mixture of conifers of varying age classes, either in clumps within the grasslands, or bordering the grasslands, provide some cover, but adjacent rock bluffs, ledges, canyons and steep slopes are critical. Visibility is an important factor for wild sheep: they select ranges where their outlook is unrestricted by standing timber, high shrubs, brush or other obstructions.
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