Watchful and difficult to approach, Dall sheep challenge the hunters, wildlife watchers, and
photographers who pursue them. The sheep too are challenged - by the harsh alpine
environments of Alaska and northwestern Canada. The animals meet this challenge because of
several unique adaptations. One place they do well is the Arctic National Wildlife Refuge.
The Refuge contains North America's northernmost Dall sheep population. Year-round
residents of the Refuge, the sheep live mostly above timberline on ridges, dry meadows, and
steep mountain slopes. There are always rocky outcrops and cliffs nearby. The sheep rarely
venture far from this rugged terrain, using it to escape predators, including wolves, golden
bears, and humans. Natural mountaineers, sheep negotiate this terrain with speed and agility.
They rarely fall.
Dall sheep eat grasses, sedges, broad-leaved plants, and dwarf willows. In winter, when
these foods are scarce, the sheep add lichens to their diet. The distribution and availability of
forage requires the sheep to move seasonally between traditional summer and winter ranges. On
the Refuge, the animals supplement their diet with regular visits to mineral licks. The sheep
usually roam in small social units, either maternal ewe, lamb and yearling groups, or groups of
Sheep forage is limited by the cool temperatures and nutrient poor soils of the northern
alpine environment. Under these conditions, the sheep mature slowly and have low reproductive
rates. Females reach breeding age at three to four years and produce only one lamb per year.
Males breed when their horns are large enough for them to establish a dominant position in the
ram hierarchy, usually at seven to nine years.
Winter weather is the main factor that affects Dall sheep numbers. In sheep habitat,
temperatures normally stay below freezing, snowfall is light, and winds sweep many ridges and
slopes, keeping snow cover light. These conditions allow the sheep good access to winter forage.
However heavy snows, temporary thaws, and freezing rains can create a frozen barrier
preventing the sheep from digging for the plants. Conditions like these can cause population
Dall sheep walk a survival tightrope, although they do it rather effectively. They have lived
since the Pleistocene in places such as the Arctic Refuge. They are one of the special wildlife
assets of this magnificent place.
September 12, 2008