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November/December 2002 issue	In this issue Table of Contents Editor’s Notebook Feature: Bighorn sheep The Inside Story Reverberations À la carte Mosaic

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Bighorn sheep facts
In Canada, there are two species of mountain sheep, each with two subspecies. The larger species is the bighorn sheep, Ovis canadensis. The two subspecies of bighorn sheep are Rocky Mountain bighorn, which occur in the Canadian Rockies, and the smaller California bighorn sheep that inhabit the arid ranges of south-central British Columbia. The other species of mountain sheep is called thinhorn or Dall sheep, Ovis dalli, which occurs in northern British Columbia, the Yukon and the Northwest Territories. Here, we will focus on bighorn sheep.

Origin: North American wild sheep are believed to descend from primitive sheep, similar to present-day Marco Polo sheep of central Asia, that migrated here 500,000 years ago via the Bering land bridge that once joined the regions now known as Russia and Alaska. When the glaciers of the last ice age spread southward, those animals became separated into two relatively ice-free areas, one in central Alaska and the other south of the Columbia and Snake Rivers. The Alaska sheep evolved into the Dall sheep, and the more southerly sheep evolved into the heavier-horned Rocky Mountain and California bighorns. As the glaciers retreated between 10,000 and 20,000 years ago, the bighorn sheep expanded their range to include British Columbia and Alberta, as well as other areas of the United States.

Distribution: Bighorn sheep are found in somewhat isolated pockets of the Rocky Mountains from southern Canada to Colorado, with a desert subspecies (Ovis canadensis nelsoni) also found from Nevada and California to west Texas and south into Mexico.

Habitat: Ovis canadensis can be found in alpine meadows, grassy mountain slopes and foothill areas near rugged, rocky cliffs and bluffs. Generally, bighorn sheep have distinct seasonal ranges, though most of the year is spent on the winter range at lower elevations. The summer range is typically between 1,800-2,600 metres in elevation, and the trigger to move to the winter range is snow accumulation. The winter range is usually at a lower elevation, between 800-1,500 metres, though the sheep may move higher if deep snow buries forage material to areas where wind and sunshine clear away the drift. The spring range is similar to the winter range, but the sheep gravitate to greening areas along streams and valleys. Bighorn sheep also use areas around saltlicks in the spring, and for lambing go to zones offering precipitous cliffs near forage.

An important requirement for bighorn sheep habitat is escape territory, such as rocky cliffs and outcrops, which allows the animals to avoid predators such as wolves, bears and bobcats. They avoid dense forests. Also, the sheep tend to stay within two kilometres of a water source. Home ranges are quite large, averaging nearly 17 square kilometres.

Physical characteristics: Bighorn sheep have brown coats and a white rump patch. In the autumn, the coat is rich and glossy, but by the spring it becomes faded and grayish. The pelage is never fine and woolly, as in domestic sheep, and is instead short and coarse. Once a year, in June or July, sheep shed their hair and can have a scruffy appearance with patches of matted hair until the new coat grows in.

Mature males are larger than females, weighing 119 to 127 kilograms and 53 to 91 kilograms, respectively. Rams typically measure 160 to 180 centimetres from head to tail, while ewes are approximately 150 centimetres. Rams stand about a metre tall at the shoulder.

Their skulls are double layered and have struts of bone for battle protection. The sheep also have a massive tendon linking the skull and spine to help the head pivot and recoil from blows. The horns may weigh as much as 14 kilograms and measure up to 125 centimetres uncoiled. The horns are never shed and grow throughout a sheep's life. Because they produce a prominent line, or annulus, each winter when growth slows, the horn is useful in telling a sheep's age. Compared to a ram, a ewe's horns are much smaller and are only slightly curved.

Senses: Mountain sheep have extremely good eyesight and can detect small objects and slight movements more than a kilometre away. This ability also allows them to accurately judge distance in jumping and locating footholds. Because of their strong eyesight and the improbability of enemies approaching on the open mountain terrain, the sheep do not have highly developed senses of smell or hearing.

Diet: Bighorn sheep primarily graze grasses and forbs but eat other vegetation depending on availability, especially in winter when food is scarce. They prefer green forage and move up- or downslope or to different aspects of the slope for more palatable forage. Important foods are wheatgrass, fescues, bluegrasses and sedges. Clover, lupines, pasture sage, cinquefoil and dwarf willow are consumed when available. Twigs and shrubs, the favourites of deer and moose, are seldom eaten.

Behaviour: Bighorn sheep are gregarious, typically gathering in groups of 8 to 10 but sometimes reaching herds of more than 100 individuals. Rams usually stay apart from ewes and young sheep for most of the year in bachelor flocks. Females tend to stay together in a group led by an old ewe, but males leave when they reach two to four years of age and join a group of rams.

Bighorn sheep are best known for the head-to-head combat between males in the mating season to gain access to females. A ram's status or rank is determined in part by the size of its horns, which are used to smash into opponents at speeds of 30 kilometres per hour. Combat goes on until one of the males concedes. It has been observed to last up to 25.5 hours, with about five clashes an hour.

Being very agile, mountain sheep are second only to mountain goats in their ability to climb steep terrain. However, while the goat is a "walker," the sheep bound like mule deer and can move much faster. They use ledges only five centimetres wide for footholds, and jump from ledge to ledge over spans as wide as six metres.

Reproduction: The rutting season, when males compete for females, is in the fall and early winter. Most bighorn sheep become sexually mature at 2.5 years of age, or 30 months. Large males can reach sexual maturity as young as 18 months, but smaller rams may takes as long as 36 months. However, because of the competition between males for females and the dominance hierarchy based on age and horns, males do not usually mate until they are seven years old, but they will mate earlier if the dominant rams of their group die. The age of maturity for ewes is highly variable, depending mainly on their physical condition. In oestrus, females will accept several rams as mates.

In Canada, lambs are born between early May and mid-June. Ewes normally have one lamb at a time, though twins sometimes occur. Gestation lasts from 150 to 180 days. Lambs are precocious, and can readily follow their mothers after a couple of days, although somewhat unsteadily. At two weeks, young sheep can eat grass. Within a few weeks of birth, lambs form bands of their own and seek out their mothers for milk only occasionally. They are completely weaned by about four to six months of age.

Longevity: The life span of individuals is affected by the whole population's status. In declining or stable populations, sheep typically live for 10 years and can reach up to 20 years of age. In a growing population with heavy reproduction, the average life span is six to seven years.

Mortality factors: In Canada, the most serious threat to wild sheep populations is a lack of good winter food. If heavy snows limit the available forage, the sheep will be concentrated on small ranges shared with domestic sheep and cattle or other wildlife such as elk. The resulting malnutrition can leave the wild sheep more vulnerable to death from disease, exposure or predation.

In healthy populations, however, predation is usually of little consequence in terms of the number of sheep taken. Golden eagles sometimes threaten bighorn sheep lambs, but are rarely successful in taking one. Bighorn sheep are an incidental food item for grizzly or black bears and wolverines, and are generally eaten only as carrion. Other predators include wolves, coyotes, mountain lions and bobcats. Humans also hunt bighorn sheep. Hunting has traditionally been for rams only and is restricted by a three-quarter or full horn curl policy.

While the sheep harbour a number of parasites, few cause mortality. However, in weakened sheep, such as when winter food is scarce, bacteria and ringworm parasites can cause major die-offs and even kill entire herds. Diseases spread from domestic sheep, such as scabies, can cause dramatic losses in areas where agricultural land is near wild sheep terrain. This has been a larger problem in the United States, but has also been seen in the Okanagan area of British Columbia.

Conservation: It is estimated that there were as many as two million bighorns in North America at the beginning of the 19th century, but today there are only about 70,000. This precipitous decline is thought to have taken place mainly between 1850-1900, and was caused by disease introduced by domestic sheep, the loss of habitat to livestock and excessive hunting by humans. Also, human activity such as the construction of roads, urban development and recreational development has impinged on bighorn territory and forced them from prime habitat, interrupted migration routes and split larger herds into smaller ones.

Luckily, recent conservation efforts have stopped the decline in some areas and a number of herds are now recovering. Some of the measures taken include the relocation of sheep from healthy populations to areas that have experienced losses or complete extirpation. As well, more restrictive hunting laws have allowed sheep numbers to increase.

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