Bighorn Sheep IN BRITISH COLUMBIA Ecology, Conservation and Management Ministry of Environment, Lands and Parks The Bighorn Sheep is remarkable for its adaptation to conditions ranging from the snow-capped alplands of the Canadian Rockies to the hot deserts of Death Valley. INTRODUCTION California Bighorn (Ovis canadensis californiana) The Bighorn Sheep is remarkable for its ability to inhabits the southwest interior of British Columbia survive in conditions as diverse as the snow-capped and extends southward on the east side of the Coast alplands of the Canadian and Cascade ranges into northern TAXONOMY Rockies and the hot deserts California. Rocky Mountain Bighorns are Order of Death Valley and northern Bighorns (Ovis canadensis canaden- Artiodactyla (Even-toed Mexico. Despite its scientific sis) are found in the Canadian appropriately ungulates) name, Ovis canadensis, the Rockies and southward along the Bighorn Sheep is more widely main chain of the Rockies to New named, adult rams Family distributed in the United States Mexico. California and Rocky Bovidae (Bison, than in Canada. Recognizable Mountain bighorns look similar, being adorned Mountain Goat, Bighorn by the massive curled horns but the California race is slightly Sheep, Thinhorn Sheep) of the adult rams and readily darker in colour, and its rams with massive Genus observed on many mountain have horns that flare outward Ovis rangelands, bighorns have long more than those of Rocky brown spiralled been a favourite subject of Mountain rams. Species photographers and naturalists. The bighorn’s name comes horns which curl canadensis from the adult ram’s massive, Subspecies EVOLUTION AND brown, spiralled horns that curl back and down californiana (California APPEARANCE back and down close to the head, Bighorn Sheep) Bighorn Sheep entered North with tips that project forward and close to the head. canadensis (Rocky America during the Pleistocene outward just below the eyes. The Mountain Bighorn ice age by crossing the Bering horns continue to grow throughout the sheep’s life, Sheep) land bridge from Siberia to but growth slows down in winter. This causes check Alaska when sea levels were lines, or annuli, whose number shows the ram’s age. lower than today. The oldest bighorn fossils in North Ram horns can be as long as 127 cm around the America are about 100,000 years old. During the most curve and as thick as 40 cm around the base. Rams recent, or Wisconsin, often wear away (or glaciation, bighorns broom) the first year survived south of the or two's growth by Cordilleran ice sheet fighting with other in the western United rams or rubbing States and northern their horns against Mexico. As the ice rocks. Ewes have sheet melted 15,000 slightly curved horns to 10,000 years ago, about 30 cm long. they gradually spread Their annuli are too northward into south- close together to tell ern British Columbia their age beyond five and Alberta. or six years. The race or sub- Bighorns are larger species known as the than domestic sheep. IN BC, ROCKY MOUNTAIN BIGHORN SHEEP ARE DISCONTINUOUSLY DISTRIBUTED ALONG THE WESTERN SLOPES OF THE ROCKY MOUNTAINS. Bill Swan Adult rams stand about 100 cm high at the shoulder In the East Kootenay region, Rocky Mountain Bighorn and usually weigh 90 to 135 kg. Ewes are about two- herds occur in five main locations: the Kootenay thirds the size of rams. Yearling rams look a lot like ranges along the east side of the Rocky Mountain ewes, but rams two years old or older have larger Trench, from Radium south to Bull River; the Galton horns. Bighorns have concave hooves with rough Range on the east side of the Trench from Elko to the foot pads that provide good traction on rocky terrain. Montana border; the Front ranges along the west side In late summer and autumn, Bighorn Sheep, of the Elk River north of Sparwood; the west slope of particularly the rams, have a rich brown coat with a the Rockies from Crowsnest Pass to Fording River; contrasting ivory-white rump patch, a white muzzle, and the Kootenay River headwaters in the vicinity and white trim on the back of all four legs. By late of Mount Assiniboine Park. More isolated herds also winter, the brown coat fades to a drab grey-brown. In occur near Golden and in the Narroway and Belcourt British Columbia, bighorns usually shed their winter drainages about 160 km north of McBride. New herds coat in June or July and look scruffy and bedraggled have been successfully estab- until the new coat grows in. lished near Chase, Castlegar, In British and Spences Bridge, which are DISTRIBUTION HOOF PRINTS outside of the historic range Columbia, AND ABUNDANCE of this subspecies, and animals In British Columbia, from an introduction in California bighorns California Bighorns occupy Washington State have spread the dry valleys and mountains into the Salmo area. occupy the dry of the Okanagan, South Cariboo, and South Chilcotin LIFE HISTORY valleys and regions. The unfavourably Bighorn Sheep are among wet, heavily forested Selkirk the most social of British mountains of the and Purcell ranges separate Columbia’s hoofed mammals. the California Bighorns territory from the natural They usually travel in groups Okanagan, South range of Rocky Mountain Bighorns. The main native of 5 to 20, occasionally up to herds of California Bighorns total about 3600 animals. 100. During most of the year, Cariboo and South They occur in the Okanagan area (Ashnola, Vaseaux ewes and rams occupy separate Lake-Penticton Creek, Shorts Creek); along the east ranges. Old ewes take charge Chilcotin regions. side of the Fraser River from about Lillooet to Williams of nursery groups consisting of Lake; west of the Fraser around Churn and Lone Cabin related females of all ages, their lambs, and yearlings Creeks; in the Bridge River watershed; in the Taseko of both sexes. Young rams leave the bands of ewes Lake-Chilko Lake area; and at the Junction of the when they are two to three years old and join bachelor Chilcotin and Fraser Rivers. California Bighorns have groups. Young ewes and rams learn the location been introduced in a number of locations, including of seasonal ranges, salt licks, and escape terrain by the Grand Forks area, Kamloops Lake, and Dog Creek. associating with older, more experienced sheep. Numbers of Rocky Mountain Bighorns in British Ram groups have well-developed social rules and a Columbia have varied dominance hierarchy or “peck order” in which a ram's from about 1500 to 3500 size, particularly the size of his horns, determines his in recent decades to position in the hierarchy. Smaller rams recognize and about 3100 today. respect the dominance of bigger ones, but similar- sized rams engage in bouts of head-butting to settle 100 0 100 200 km who is the boss. This occurs throughout the year, but PLENTIFUL it is particularly pronounced among mature rams at MODERATE breeding (rutting) time, when dominance usually FEW confers the right to breed with any receptive ewes. ABSENT However, smaller rams may mate with receptive ewes while the larger rams are busy fighting. Rocky Mountain Bighorn Sheep Most ewes do not breed until they are two years old, but where nutritional conditions are very good, a few may breed as yearlings. Rams are physiologically California Bighorn capable of breeding by two years of age, but they Sheep Young animals usually have to stay on the side- deficiencies of key trace minerals, changes in diet, lines until they are seven or eight poor nutrition, overcrowding, and inclement weather learn the location years old. appear to be factors in these die-offs. California In southern British Bighorn Sheep do not appear as susceptible to of seasonal ranges, Columbia, Bighorn Sheep breed pneumonia epidemics. between early November and salt licks, and mid-December. Gestation lasts ECOLOGICAL RELATIONSHIPS from 170 to 180 days, and lambs Bighorn Sheep are best suited physically and behav- escape terrain by are born from the last week in iourally to rugged, mostly treeless terrain, to foraging April to early June. As lambing sites with low-growing grasses and herbs, and to associating with time nears, pregnant ewes leave regions with shallow snow cover. These requirements their social group and isolate greatly restrict their distribution in British Columbia. older, more themselves in rugged lambing Bighorns occur only where the climate is driest because cliffs near the winter-spring those areas support natural grasslands and have the experienced sheep. range. They usually produce a least snowfall. single lamb that weighs 3 to 5 Many California Bighorn Sheep spend the winter and kg, but some well-nourished females produce occa- spring on low-elevation grasslands in the Bunchgrass, sional twins. After a few days of nursing and bonding Ponderosa Pine, and Interior Douglas-fir zones. These in the cliffs, mother and lamb rejoin the ewes’ social scattered sites, at elevations of from 300 to 1825 m, group. Bighorn lambs grow rapidly through their first tend to be steep, south- to summer and weigh about 30 kg by autumn. As summer southwest-facing, and domi- Most migratory progresses, lambs eat more plants and suckle less often. nated by bluebunch wheat- By about October they are weaned. grass. They consist of rugged bighorns in British Bighorn Sheep die from predation, starvation, acci- breaks and terraces along river dents, and disease. These factors kill about 50 percent valleys, rocky outcrops, and Columbia leave their of the lambs and 20 percent of yearling sheep each grassland tracts surrounded year. After the age of two, the sheep are less vulnerable, by Douglas-fir forest. In winter ranges in May but the death rate increases again when they get old.