Dall Sheep

The Dall sheep, also known as stone’s sheep or the thinhorn sheep, is a wild social animal native to the northwestern part of North America. The name “Dall” was given after William Healy Dall, a scientist who led surveys in Alaska during the late 1800s.

This Sheep is further categorized into two subspecies, Ovis dalli dalli, and Ovis dalli stonei.

Description

Size: Length: Male: 4.3-6 ft (1.3-1.8 m) Female: 4.33- 5.31 ft (1.32-1.62 m)

Height: 3.01-3.58 ft. (92-109 cm)

Weight: Male: 160-180 lb (72-82 kg);  Female: 100-110 lb (45-50 kg)

Horns: The approximate measurement of the horn is 46.87 inches (1.19 m). Horns are thin and light brown colored. Rams’ horns are massive, curled, and flaring, while ewes’ are slender and shorter. It grows annually in both males and females during spring and summer. The growth slows down around early fall and stops in the winter. This start-stop growth process results in ring patterns occurring around the horns. These rings are called annuli.

Body and Coloration: The Dall sheep are off-white with a coat that consists of an undercoat of fine wool and long stiff guard hairs. During winter, their coats’ thickness can get over two inches. The males are usually larger in size than the females and could be easily distinguished. However, young rams look very similar to ewes.

In winter, the adults lose their body mass by up to 16%, and yearlings and lambs lose up to 40%, depending on the severity of the weather. 

Range and Distribution

The Dall sheep have limited distribution. They are found in Alaska’s Arctic and Subarctic mountain ranges, including Brooks Range, Chugach, the Denali National Park and Preserve, Kenai, Mentasta, Nutzotin Mountains, Tanana Hills, the northern part of Wrangell Mountains, and the White Mountains. This sheep is also found in central and northern British Columbia, the Yukon Territory, and the Mackenzie Mountains in Canada.

Habitat

These sheep have a wide variety of preferences in habitat, with the alpine tundra being the most favored. They live at an altitude of up to 6,560 ft (2,000 m). Other places they inhabit are dry mountainous regions, rugged cliffs, outcrops, and meadows. Their home range covers 20-60 square miles.

In winter, Dall sheep migrate to regions with strong winds and less snowfall.

Diet

Their diet varies depending on the season. During summer, these sheep consume 50-120 types of plant species, including forb, grass, lichen, willow moss, and sedge. In winter, the food sources are low, and they rely on 10-15 kinds of plants, mostly feeding on frozen grass, lichen moss, and sedge stems. To restore the minerals in their body, they visit ‘mineral licks’- areas abundant with necessary minerals such as calcium.

Behavior

• Dall sheep are diurnal species.
• They maintain social order and dominance among the folds. 
• To establish social order, rams engage in dramatic clashes. They start by running at each other and then collide their horns. They show other behaviors in establishing social order, like bluff charges and leg kicks. 
• As the mating season approaches, these clashes intensify between the males with the same horn size.
• Males with larger horns have higher ranks among other rams.
• Rams and ewes do not travel in the same group except for the mating season.
• Competitive behavior among ewes can be seen occasionally over bedding and feeding sites.
• The males cover up to six different ranges throughout the year, and the females cover up to four.

Lifespan

The lifespan of a Dall sheep ranges between 12-16 years, with 10 years being the average. 

Adaptations

• When forced to come down from steep slopes during winter, their white coat helps them camouflage in the snow from predators.
• Their woolen coat protects them from low temperatures.
• Air sinuses in the rams’ skulls help them absorb the impacts from head slamming against horns, heads of other rams, etc., that could severely injure or even kill them.
• They have cloven hooves with strong pads that make walking around on the rocky terrain easier.

Mating and Reproduction

The Dall sheep are polygynous. The breeding season, known as the rut, lasts from November to early December. Males guard females for three days after mating, then move on to find new mates. After a gestation period of 175 days, females give birth to a single lamb that weighs about 6.6-8.8 lbs (3- 4 kg). The births take place between the middle of May to early June.

The lambs are precocial, meaning they can walk and travel with their mother only a day or two after birth. Mothers give birth on rugged cliffs for protection and solitude. The pair remains on the cliffs until the lamb is strong enough to travel. After 3-5 months, they are fully weaned. Rams and ewes become reproductively mature at 18 months and 30 months, respectively. However, the rams start mating at the age of 5-7 years, when they have achieved social dominance. Ewes give birth for the first time at 3-4 years old.

Predators

The Dall sheep’s natural enemies include bears, coyotes, lynxes, wolves, and wolverines. Sometimes golden eagles prey upon the lambs.

Conservation Status

According to the IUCN, the Dall sheep is “Least Concern” or “LC”. However, the population is threatened by trophy hunting, habitat fragmentation, etc.

The estimated number of mature individuals is 66,600 globally.

Interesting Facts

•  A Dall sheep’s age can be predicted by counting the number of annuli.
• This sheep’s horns are made of keratin, the same fibrous protein that makes human nails. 
• When dark hairs appear on a Dall sheep’s body, it is called a Fannin sheep. However, those with black tails are still considered Dall sheep.
• These sheep are often compared with bighorn sheep and mountain goats. Compared to this sheep, the bighorn sheep have slightly short and thicker horns, and mountain goats have less curvy and black horns.