Spotlight on California Big Horn Sheep of the South Okanagan Similkameen
Photograph courtesy of Bob Lincoln |
California Bighorn Sheep were once distributed widely throughout the dry, rugged grasslands and rocky cliffs of the South Okanagan Similkameen. Now, these magnificent animals occur only in relatively small, isolated populations. They remain however, one of three populations vital to the conservation of California Bighorns in British Columbia, which represent a considerable portion of the world population.
Latin Name: Ovis Canadensis Californiana
Federal Status: Threatened
Provincial Status: Blue Listed (vulnerable)
Characteristics
The California Big Horn Sheep are ungulates, which are hoofed mammals that chew their cud and are horned or antlered. Bighorn sheep are related to cattle, antelopes and goats. Adult rams are typically between 70 to115 kg and adult ewes between 50 to 75 kg. California Big Horn Sheep have greyish-brown to dark brown coats, a short dark tail that is outlined by a large white rump patch. Adult males have massive curling horns, which develop to form a full circle. The female horns are thinner and rarely exceed 25 cm. The maximum lifespan is 12 to 14 years.
Tracks
The track of the Bighorn Sheep has a straighter edge and is less pointed than that of the deer with a blockier shape and small hollow on the inside of the hoof. Regardless of these differences, the tracks of the deer and Bighorn Sheep are easily confused.
Habitats
In the South Okanagan Similkameen, California Big Horn Sheep depend upon several habitat types for their survival; rugged terrain, coniferous forest and grasslands. Their habitats are varied according to the seasons. Bighorn sheep require two types of winter range in close proximity. These are referred to as normal winter range and severe winter range. The “normal” winter range has access to food and escape terrain. 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. Severe winter range has large canopied trees for relief from deep snow. Escape terrain is critical for avoiding predators and is provided by cliffs and rocky slopes. 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.
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 used between the winter and summer months.
Distribution
In the South Okanagan Similkameen, Bighorns occur in scattered herds in the Ashnola River system, the east side of the South Okanagan Valley, and Shorts Creek west of Okanagan Lake. During winter, bighorns come down into the valley bottoms, around 600m, in the summer they will range in the highlands up to 1550 meters.
Behaviour and Breeding
Breeding takes place on high, grassy slopes of the winter range, and lambing generally occurs on escape terrain characterized by steep rocky bluffs or areas of steep, rugged terrain adjoining the winter range grasslands. 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 six months with ewes giving birth to usually one lamb (occasionally twins) from April to late June.
Diet
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 antelope brush, sage, saskatoon, mock orange, bearberry, juniper and willow.
Threats
- Loss of habitat and difficulty moving between habitats due to urban development.
- Presence of domestic sheep, which can transfer fatal diseases to wild sheep.
- Encroachment of invasive plants which have low nutritional value and out-compete native grasses.
- Deterioration of grasslands by recreational activities such as off-road vehicles.
- Recreational activities in rocky habitats disturbing the sheep, especially during lambing.
- Introduced predators, such as domestic dogs, which wound and kill sheep, and chase pregnant ewes.
- Road mortality affects local population of sheep each year.
What you can do
- Protect sheep habitat by practicing Smart Growth and avoiding urban sprawl into high quality sheep habitat.
- Practice double fencing to keep domestic sheep away from Bighorn sheep range.
- Enjoy sheep from a distance by using binoculars and keep dogs under control.
- Be extra cautious around the rams during the rutting season in November, because they are aggressive and may charge you.
- Slow your vehicle when sheep are near a road or highway, and avoid approaching them too closely, thereby causing them to run onto the road.
- Keep away from known lambing areas from April to late May.
- Be aware of sheep movement corridors in your neighbourhood and help to preserve them in a natural condition.
- Preserve areas of natural habitat on your land in as large and continuous a tract as possible.
- Preserve natural ponds or springs used by sheep as a water source.
- Learn more about aggressive European weeds and how to control them.
- Keep grasslands undisturbed by walking or driving on established roads and trails only.
Recovery Actions
When a pneumonia-related die-off in 1999-2000 killed approximately 65% the South Okanagan bighorn sheep population, a plan was introduced to recover its population numbers. In 1999, the South Okanagan bighorn population was approximately 450. After the bacterial pneumonia epidemic the population estimate dropped to approximately 140. Wildlife biologists have worked to study and recover the herds of the South Okanagan including augmenting numbers by transplanting animals from other populations. The total current bighorn population estimate for the south Okanagan is between 350 and 400 individuals.
In 2007 and 2009, due to the improvement of habitat from the wildlife of 2003, Okanagan Mountain Park became the next centre for bighorn sheep recovery. Roughly 50 bighorn sheep have been transplanted to the park from larger, more robust herds on two occasions. The Park is within bighorn historic range but had not supported a permanent population in recent years, because of habitat deterioration due to fire exclusion. Monitoring in 2009 showed some encouraging numbers for this growing population, including healthy numbers of lambs. Recovery for these herds is slow, but showing excellent signs of success.
Protecting habitat for Bighorn sheep will also benefit many other species including these associated species at risk:
- Canyon Wren.
- Pallid Bat.
- White Headed Woodpecker.
- American Badger.
- Rubber Boa, Night Snake, Western Rattlesnake and Great Basin Gophersnake.
- Prairie Falcon.
- Peregrine Falcon.