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Bighorn Sheep

Blue Listed Species

Human Health Hazard

Conservation Status

Syilx 

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Description

California Bighorn
Sheep have a dark to medium rich brown head, neck,
and dorsal body with a short black tail and a white
muzzle, rump, and ventral patches. Both sexes have
sturdy muscular bodies and strong necks that
support horns that curve back in females and are
much larger and curled around in males.

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. 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.

Food

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.

Social System, Activity & Movements

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. "Seasonal home ranges may vary considerably between Bighorn Sheep herds, not only in size, but also in the distance to other seasonal home ranges. The separation of one seasonal range from another can be one steep gorge or it can be distances of 10– 70 or more kilometres between summer and winter ranges for California Bighorn (Blood 1961; VanSpall and Dielman 1997) and 24 to >51 km for Rocky Mountain Bighorn. Ewes in central Idaho migrated 1–40 km from winter ranges to lambing ranges (Akenson and Akenson 1992). Unlike Rocky Mountain Bighorn Sheep observed by Geist (1971), the radio-collared California Bighorn Sheep studied in the Churn Creek watershed (Fraser River metapopulation) did not demonstrate a difference between sexes in the timing of either spring or fall migrations. Ewes and rams migrated concurrently between the summer and the rutting/wintering areas, spending approximately 8 months on the winter range (Keystone Wildlife Research 1998). However, high water flows did delay spring migrations of ewes accompanied by lambs.

In late September or early October, large bands of rams move to a fall concentration area where they generally stay from 2 to 5 weeks. From this pre-rut range in the first week of October or the first week in November, they disperse to rutting grounds until the end of December (Geist 1971; TAESCO 1982). At this time some rams will return to pre-rut home range while others move to mid-winter home ranges where they spend 271–303 days (Geist 1971). Some young rams and the ewes will remain at the rutting grounds. By mid-March, rams return to fall concentration areas. In summer, the rams move to salt licks for a few weeks and then to summer range.

Ewes arrive later on the wintering areas and depart earlier, spending 240–268 days on wintering areas (Geist 1971). The fall concentration area or areas immediately adjacent will usually be where the ewes remain in the winter. In late March or April, separate winter/spring range may be used once the snow hardens or is reduced enough to allow movement. Females move to lambing areas in late May or June or, infrequently, at the beginning of July. Pregnant ewes were found to move from higher quality forage to an area of lower quality to provide better protection from predation Lambing may take place on the winter range or in a separate lambing range. In late June or early July, barren females, juveniles, and rams move to summer ranges.
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Reproduction & Parental Care

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.

Natural Mortality & Predators

Maximum lifespan is 12-14 years.

Credit

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Habitat
Food
Social System, Activity & Movements
Reproduction & Parental Care
Natural Mortality & Predators
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