ENVIRONMENT YUKON
Camping & Wilderness Parks & Conservation
Wildlife &
Biodiversity		 Monitoring the
Environment
Fishing Hunting & Trapping
Education
& Youth		 Publications,
Maps & Data

Thinhorn Sheep

THE SPECIES: Ovis dalli 

sheep.jpgDashing across alpine meadows, clinging to sheer rock faces, or grazing sedately at treeline, thinhorn sheep are true mammals of the mountains. If you have seen a band of thinhorns, be they majestic rams or ewes with playful lambs, you will know why these graceful mountain sheep are one of Yukon's best-loved wildlife species.

Thinhorn sheep are a New World species found only in Canada's northwest and in Alaska. They are close cousins to Siberian snow sheep and were once thought to be the same species.

Two subspecies of thinhorns inhabit the backbone of the northwest today. Pure white Dall sheep occur in Alaska and parts of Yukon, Northwest Territories and British Columbia. The darker Stone sheep occupy a smaller range in Yukon, but occur throughout much of northern British Columbia.

DISTRIBUTION

From our southern border to near the arctic coast, Yukon mountains are home to 22,000 thinhorn sheep. Of these, there are about six times as many Dall sheep as Stone sheep. The white thinhorns are abundant southwest of the Yukon River, but are spread more thinly in scattered northern pockets and within a broad band that arcs across central Yukon.

Stone sheep occur in small pockets in the south, but are more widely dispersed in the northern part of a range that stretches like a tongue from the British Columbia/Yukon border to central Yukon. More and more sightings of coloured sheep are being reported in areas that used to have only white sheep.

One of the reasons why northern Yukon sheep populations are sometimes only half as dense as southern ones may be that critical habitat features are fewer and farther between in the north. Such features include lambing cliffs, mineral licks, safe migration routes and good winter range.

CHARACTERISTICS

Dall sheep are typically pure white,whereas Stone sheep have gray, brown or black coats and white muzzles, bellies and rump patches. It may seem odd that there are such differences in colour within the same species, but it makes sense when you think about Yukon's natural history.

The last time glaciers pushed their way out of the icefields, they split up sheep populations and left them in very different habitats. Some lived high on snowy alpine slopes close to the massive rivers of ice, while other sheep lived low-er on more heavily treed mountains. White sheep blended in with the snowy alpine environment, while dark sheep blended in with treed surroundings. Animals that did not blend in with their environment were more likely to be targeted by predators, and so the two forms diverged.

Today, Yukon thinhorns run the gamut in colour from white to almost black, with every conceivable combination between. This range is most pronounced in the central Yukon where the Dall and Stone sheep subspecies overlap and interbreed. One striking example of mixed colours is the Fannin or saddle-back sheep of the Faro area. It has a dark "saddle" on an otherwise white coat. All these colour variations make it difficult for people trying to classify sheep into one of the two subspecies: Dall or Stone sheep. Right now, all Yukon coloured sheep are lumped to-gether as Stone sheep, which is why Stone sheep range seems to be expanding.

Both ewes and rams have curved horns. Ewes' horns are gently backswept and quite short. Mature rams' horns curve first back and down, then forward and up in a flaring spiral. The length along the curve of a ram's horn can be more than one meter. Rams have much thinner horns than those of Rocky Mountain bighorn sheep, hence the name "thinhorns".

Our northern mountain sheep are also lightweights compared to bighorns. Thinhorn rams weigh up to 115 kilograms, about two thirds the weight of bighorn rams. Stone rams are usually somewhat heavier than Dall rams and also have slightly longer horns. Ewes are a fifth smaller than rams and weigh only half as much.

MOVING WITH THE SEASONS

Thinhorn sheep spend the short northern summer grazing in high alpine meadows. During July and August they crop the choicest bits of grasses, sedges and juicy, broad-leaved forbs. They are building up fat stores to help them through the winter, when high quality forage doesn't last as long as the snow and cold.

Come late August and September, thinhorns begin a leisurely move toward winter range that can be few or many kilometers away. They use the same migration routes generation after generation, drifting slowly through the high country, but hurrying across valleys that must be crossed. Once sheep leave the safety of rugged mountain terrain, they are open to attack by wolves, coyotes or grizzlies.

Wind-swept, south-facing slopes at fairly low elevations are typical thinhorn winter range, and sheep spend up to nine months there. Dall sheep usually stick to open grasslands above treeline while Stone sheep also make use of treed and shrubby areas. For both kinds of thinhorn, winter range must have scree slopes and broken cliffs nearby for escape routes and for spring lambing grounds.

Since sheep are grazers, they need to get at grasses and other favorite plants buried by winter snowfalls. They will dig in snow up to 30 centimeters deep, but rely on strong winds to sweep the slopes clear of deeper snow. Freeze-thaw weather and heavy, wet snowfalls can lock sheep food beneath a crusty barrier, which can have serious consequences. If ewes don't get enough food energy during the winter, they don't produce lambs and the population declines.

In spring and early summer, sheep often visit mineral licks to restock their supply of micronutrients lost during the long winter. They spend days or weeks near the licks before following the line of snowmelt and newly sprouted green shoots back up to alpine summer ranges.

Spring also brings lively new life to the mountain slopes. Pregnant ewes head for the lambing grounds' steep cliffs in May and early June. There they stay for three to four weeks until all lambs are born. Then, together with their young, they climb to summer range once more.

THE SOCIAL SIDE OF LIFE

Thinhorn sheep are social animals that minimize squabbles within their ranks by sticking to a rigid dominance scale based on horn size. The ram with the largest horns tops the scale and treats all other sheep, regardless of sex or age, as subordinates. Every thinhorn has its place and things run smoothly as long as sheep don't try to jump rank.

The Ram Band

Rams aged three years and older band together and go their own way for most of the year. They often seek out higher summer pastures than ewes and young sheep, and mix with other sheep on winter ranges for only a month or two. Leadership clashes within the band can happen any time of year, but are fiercest during the rut in November and December. Young rams move up through the ranks very slowly and are five to seven years old before they have large enough horns to challenge a leading ram. Thinhorn rams aren't as aggr-essive as bighorns, but top rams still put a lot of energy into defending receptive ewes from other rams challenging their dominance. These rams rarely live to 12 years, whereas ewes may reach 16 years of age.

The Nursery Band

Ewes, young rams and brand new lambs remain together throughout the year and have little contact with the ram band except during winter months.

Newborn lambs, weighing about three kilograms, race and frolic within days of birth but may fall prey to cold weather, accidents, or eagle attacks. They quickly learn to nibble choice grass shoots and to rely on their own fleet feet to escape danger. While watchful ewes graze and rest in a loose circle, the lambs within scramble up cliffs and slide down scree slopes, building strong bones and muscles and practising for the real escapes. Through playful jousting, lambs find their place in the thinhorn scheme of things, which is far below the band's leading older ewe.

As the nursery band moves onto summer range, lambs learn traditional travel routes and begin to eat more grasses, sedges and herbs. By the time they are weaned in autumn, they weigh 10 times as much as they did at birth.

THINHORNS AND PEOPLE

In the old days, as now, thinhorn sheep were prized for their delicious meat. Yukon First Nations hunters stalked the sheep with bow and arrow or set rawhide snares in narrow places, then drove their quarry into the snares.

Hunting the mountain dwellers was difficult and dangerous work, so long-ago hunters and their wives followed strict rules before and during a hunt. Some hunters ate only cold food the day before a hunt. And while they stalked sheep among the peaks, their wives did not comb their hair for fear of "combing" the hunters over the cliffs. Other women did not eat hot food or heat water during a hunt, in case they should cause the ice and snow to melt and slide down upon their husbands.

So vital was the wild sheep to the livelihood of these peoples that a legend is told of the great flood and how the first couple to survive it set a snare and caught a mountain sheep as the waters ebbed. As well as eating sheep meat, First Nations peoples made blankets, jackets and winter pants from sheep fleece; and ladles and dishes from horns of the great rams.

During the gold rush years, a flood of prospectors and hunters supplying meat to new settlements nearly destroyed entire populations of the wild mountain sheep. Later, road crews building the Alaska Highway also took a heavy toll of sheep in southwestern Yukon.

Today the thinhorns have recovered from past ravages . Since mountain sheep use the same migration routes and seasonal feeding grounds generation after generation, they are still vulnerable to habitat destruction and disturbance.

Thinhorn sheep, especially the Fannin sheep, are perhaps the most prized trophy animals in North America and the mainstay of Yukon's big game outfitting industry. As well, more and more people stalk them with only a camera or the naturalist's eye. They are thrilled simply to capture some of the magic of the mountains that these wild sheep evoke.

VIEWING OPPORTUNITIES

Highway travellers have some excellent chances to see thinhorn sheep on traditional feeding grounds. A favorite spot is Sheep Mountain in Kluane National Park, home to about 200 Dall sheep that wander over its south face from September through May. The Alaska Highway skirts the base of the mountain, offering superb viewing. The sheep are easy to spot when the ground is bare, but harder to see after snowfall. Look for yellowish lumps on ridges and open slopes.

Several secondary roads provide access to anot-her "Sheep Mountain" just east of Faro. It is the winter range of about 90 Fannin sheep and is the only Yukon location where coloured thinhorns can be easily seen at close range. During the summer months you can use binoculars to spot Dall sheep on the hills behind the Kusawa Lake campground, off the Alaska Highway. On the Dempster Highway, a mineral lick near Engineer Creek is a roadside attraction for Dall sheep in June, making for easy viewing of majestic rams.

Rafters can see Dall sheep from the Firth River in northern Yukon. Other river travellers may be able to spot sheep at a distance on high ground, so keep binoculars on hand and glass the slopes once in a while.

Hikers have the best chance of spotting thinhorns during the summer months when they are grazing high in alpine meadows. Low ground cover and open vistas above treeline make viewing both easy and spectacular. Unprotected sheep are very wary and spook easily, but protected thinhorns often become quite tame and may pose for the picture of a lifetime. Hikers should take care to not disturb nursery band ewes and lambs since they operate on a tight energy budget.

I DENTIFICATION

A full-curl ram in plain view is easily identified as a thinhorn sheep, but it's tougher to be sure about something away up there in the rocks. If it's white and you're in southwestern Yukon or the Logan Mountains, it may be a mountain goat.

To be sure it's a thinhorn sheep you're seeing, check the following features:

Horns

Coat

Hump

DID YOU KNOW ?

 

Last Updated: December 31, 1969 | © 2008 Government of Yukon | Copyright | Privacy Statement | Disclaimer