The Dall Sheep (Ovis dalli) are completely at home in their winter surroundings of the far northern mountains. These white sheep are found only in central and Northern Alaska, the Yukon Territory, and northern British Columbia where mountain ranges provide favorable habitat because the snowfall is relatively light and strong winds keep the exposed ridges free of snow. The large amber-colored horns of the rams, with transverse ridges and sweeping outward curl, have a rugged, graceful beauty. They may spread widely at the tips or curl rather close to the head. The ewes’ horns are slender spikes that extend upward in a slight curve, resembling those of the mountain goat, but they lack the shiny jet black color and are not as sharp. The horns are never shed and continue to grow throughout the sheep’s life span of eleven to fourteen years. The growth is slight during the later years. (unlike horns, antlers are shed annually, such as those of moose and caribou). Horn growth takes place during the summer when food is highly nutritious. These horns grow from the skin over a conical bony core. In winter, only a groove or ridge encircling the horn is formed. By counting annual rings the age of a sheep can be determined.
The rams will use their horns to butt each other in sparring, a technique which helps establish the social order of the band. Clashes can occur throughout the year but they are more frequent and serious during fall breeding when large rams engage other rams with similar horn size. A battle between two powerful, well-matched rams is an unforgettable sight. After backing off 30 or 40 feet they rush together and collide headlong. The echoing crash can often be heard over a half mile away. Perhaps the true meaning of the word “ram”! Luckily, a double layer of bone on the skull roof protects the antagonists from brain damage. The most active mating period extends from the middle of November to the middle of December after increasing snow has forced the sheep to descend from their summer range.
As mating activity lessens, in late December and January, the rams drift away from the ewes and form bachelor groups. The winter is spent on relatively small ranges of south-facing, exposed grassland, where the sheep paw through shallow snow to find food. Lambs are born between early May and mid-June and weigh 5 to 6 pounds at birth. Normally one lamb is born per ewe, although twins occur occasionally. By their first winter they weigh 60 to 70 pounds. Dall rams can be 3 and 1/2 feet tall at the shoulder and weigh up to 160 pounds; ewes are about 20 percent smaller. Mountain sheep have eight sharp teeth at the front of the mouth. These are called incisors and are used to cut off plants. Their remaining teeth (molars and premolars) are deep rooted, and adapted for chewing. All the teeth are gradually worn down by the grit which the sheep picks up as it feeds.
Mountain sheep occupy alpine ridges and steep slopes adjacent to extremely rugged terrain, where they can flee from predators. Sheep are subject to wolf predation, especially when their numbers are so high that part of the population must graze on hills too gentle for safety. The very old, the ailing, and the lambs in their first winter are the most vulnerable to predation. When hare numbers have crashed lynx may go after Dall sheep, along with wolverine and grizzly bears on occasion but their effect on population numbers is unimportant according to most biologists. Probably the most serious threat to wild sheep numbers is lack of good quality winter food.
The esthetic appeal of this beautiful animal and the setting they occupy, of precipitous cliffs and ledges intermingled with green slopes carped with summer wildflowers attributed to the designation of Denali National Park (then called McKinley National Park) as a wildlife refuge in 1917. This idyllic country and its wild occupants is Alaska’s greatest resource.