Habitat Atlas for Wildlife at Risk
California Bighorn Sheep
Ovis canadensis californiana

• Weight: adult rams, 70-115 kg; adult ewes, 50-75 kg.
• Length: rams, 1.5 metres; ewes are approximately 15 percent smaller.
• Coat greyish-brown to dark brown.
• A short dark tail is outlined by a large white rump patch; a band of white trim outlines the backs of all four legs.
• Adult males have massive curling horns which develop to form a full circle.
• Female horns are thinner and rarely exceed 25 cm.
• Maximum lifespan is 12-14 years.

Status:

British Columbia Blue List

Special Significance

California Bighorn Sheep no longer occur in many areas of the Okanagan because of degradation of habitat, changes in predation mortality and historical over-harvest by legal or illegal hunting. The invasion of non-native plants, intensive cattle grazing, fire suppression, timber harvesting, and land development are factors that have limited access to forage plants. Sheep survival depends on familiarity with their habitat and they are slow to re-occupy vacant habitats.

Distribution

• In British Columbia, bighorns occur in scattered herds in the Ashnola River system, the east side of the South Okanagan Valley, 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 transplanted herds have been established, near Kamloops Lake and Grand Forks.
• In the South Okanagan elevational range during winter is often below 600 m but can range up to 1800 m; summer range elevation can range from lake level to 1550 metres.

Habitat

• Winter range is the limiting habitat for bighorns; two types of winter range in close proximity are required: normal winter range with access to food and escape terrain, and severe winter range with large canopied trees for relief from deep snow.
• Escape terrain is critical for avoiding predators and is provided by cliffs and rocky slopes, and dense timber patches bordering winter foraging sites.
• Normal winter range includes low elevation, bunchgrass ranges on south and west facing slopes, mature open ponderosa pine or Douglas-fir forest, rocky bluffs, and dry, open rocky areas with scattered scrub timber; sheep avoid closed forests and areas with a snow cover of greater than 15 percent.
• Many herds do not have available alpine habitat typical of summer range, and remain in one general location year-round; some herds in the Ashnola spend summer in subalpine forest, or open forest below the subalpine.
• Rutting grounds generally occur on ewe winter ranges.
• Breeding takes place on high, grassy slopes of the winter range, and lambing generally occurs on escape terrain (steep rock bluffs or expansive areas of steep, rugged terrain) adjoining the winter range grasslands (characterized by rich soils with abundant spring grassland forage).
• Bighorns are predominantly grazers, relying on grassland habitats; ewes without lambs and rams are generally found foraging in open grass slopes and agricultural areas; ewes with lambs are more likely to forage in bluff tops and talus slopes during late spring, and grass slopes with rock outcrops from late spring to autumn; in late summer, they may also be found in open canopy forests adjacent to rock bluffs; spring forage sites are generally found on south or southwest aspects.
• Open forested habitat is usually used during transition, however less suitable habitats may also be used; sheep migrate quickly through densely forested habitat, avoiding areas of human disturbance, including major roads, which are often crossed at night.

Reproduction

• Breeding occurs in the Ashnola from late November to early December; on the east side of the South Okanagan Valley, the rut occurs from mid-October to late December.
• Gestation period is approximately 6 months; ewes give birth to usually one lamb (occasionally twins) from April to late June.

Food Habits

• Grasses, sedges and soft-stemmed plants comprise the majority of the diet, but up to 25 percent of diet may be comprised of shrubs such as sage, saskatoon, mock orange, bearberry, juniper and willow.

Interesting Facts

• Rams over three years old usually segregate into separate bands from ewes, young and sub-adults. Rams assess their body weight and condition, relative to other rams, by head butting. The ram that rebounds most in these violent clashes is the lighter of the two. Ram groups establish and maintain a social hierarchy through head butting and other displays.

References

1. Banfield, A.W.F. 1977. The mammals of Canada. Published by the University of Toronto Press.
2. Takoff, M.E. 1988. Draft. Lamb production, lamb mortality and habitat use of the Vaseux band of California bighorn sheep. Ministry of Water, Land and Air Protection Lands and Parks, Penticton, British Columbia.