Dall Sheep

Dall Sheep (or the Ovis dalli) inhabit the mountain ranges of the Alaska region. These white creatures are very notable for the massive curled horns of the males. Females (called ewes) also carry horns, but theirs are shorter and slender and only slightly curved. Until rams reach the age of 3, they tend to resemble the ewes quite a bit. Later, continued horn growth makes the males recognizable easily.

Horns grow steadily during the seasons of summer, spring, and early fall. In winter or late fall, horn growth slows and ceases eventually. This start-and-stop growth results in the pattern of rings, which are called annuli, spaced along the length of the horn and may help determine the age. Dall rams older than 16 years have been seen, and the ewes have been known to reach 19 years. However, in general, a 12-year-old sheep is considered quite old.

Taxonomy and Genetics

Past research had represented the use of pelage-based subspecies designations was questionable. A complete colour intergradation takes place in both thinhorn sheep subspecies (it means, Stone'sStone's and Dall'sDall's), ranging between dark and white morphs of the species. Intermediately coloured populations, which are called Fannin sheep, were originally identified as unique subspecies (O. d. fannini) with the distributions inhabiting in the Ogilvie Mountains and the Pelly Mountains of the Yukon Territory.  Fannin sheep are more recently confirmed as admixed individuals with predominantly the sheep genetic origins of Dall.

Dall sheep (Ram and Ewe) are figured below.

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The previous mitochondrial DNA evidence had exhibited no molecular division along the earlier subspecies boundaries, although the evidence from nuclear DNA can provide support. Current taxonomy using the mitochondrial DNA information can be less reliable because of hybridization between O. canadensis, and O. dalli recorded in evolutionary history.

Current genetics analyses with the help of a genome-wide set of single nucleotide polymorphisms (SNPs) has confirmed that new subspecies range boundaries for both Stone'sStone's and Dall'sDall's sheep, updating the previous pelage-based and the mitochondrial DNA classifications:

• A genome-wide set of SNPs reveals the evidence for two admixture and glacial refugia from postglacial recolonization in an alpine ungulate.

• Management implications of the highly resolved hierarchical population genetic structure in the thin horn sheep.

Dalli, the specific name is derived from William Healey Dall (1845–1927), who is an American naturalist. Often, the common name Dall sheep or Dall'sDall's sheep is used to refer to the nominate subspecies, O. d. dalli. The other subspecies, O. d. stonei is known as the stone sheep.

Growth and Reproduction

Lambs are born to the ewes either in late May or early June. As the lambing time approaches, ewes seek solitude and protection from the predators in the most rugged cliffs available on their spring ranges. Lambs start feeding on vegetation within one week after birth, and they are usually weaned by October. Typically, ewes have their first lamb at the age of 3 or 4 and produce a lamb annually.

The first weeks of the lamb's life are precarious. The mortality's bulk is in the first 30 - 45 days of life when the lambs are vulnerable.

Adult rams live in bands that seldom associate with ewe groups beyond the mating season in both late November and early December. The horn clashing, which rams are very well known for, does not result from fights over possession of ewes, but it is a means of establishing order. These clashes take place throughout the year on an occasional basis but take place more frequently just before the rut when rams are moving among the ewes and meet their unfamiliar rams of similar horn size. Rams may sire offspring at 18 months of age, but they do not regularly breed until they approach dominance rank (at full size and curl age).

Feeding Ecology

The diets of Dall sheep differ from range to range. Food is abundant during summer, and a wide range of plants are consumed. The Winter diet is more limited and consists majorly of frozen grass, dry, and sedge stems available when the snow is blown off the winter ranges. A few populations use significant amounts of lichen and moss in winter. During the spring, various Dall sheep herds visit mineral licks, and they frequently travel several miles to eat the soil at these peculiar geological formations.

As many different bands of sheep meet at the mineral licks, ewe and ram groups can mingle, and the young rams join the ram band that happens to be present at the time. This random contribution of young rams to different ram bands can benefit sheep by maintaining genetic diversity. Sheep are loyal to their home ranges, and mineral licks are good spots to see sheep due to the animals being so intent on eating the dirt they pay attention to humans. However, the major disturbances such as operating machinery readily drive sheep from the mineral licks or low-flying aircraft.

Natural History

Ecology

The sheep inhabit the subarctic mountain ranges of the Alaska regions, the Mackenzie Mountains in the western Northwest Territories, the Yukon Territory, and northern and central British Columbia. Dall sheep are found in the relatively dry country, and they try to stay in a special combination of meadows, open alpine ridges, and steep slopes with the extremely rugged ground in the immediate vicinity to allow escape from the predators which cannot travel quickly through such terrain.

Male Dall sheep have curling and thick horns. The females have more slender, shorter, slightly curved horns. Until the age of 3, both male and female Dall sheep appear to be the same. Past that age, males are distinguished easily by their horns that continue to grow steadily in the summer, spring, and early fall. This results in the start-and-stop growth pattern of rings, known as annuli. Annuli may be used to help in age determination.

Males live in bands and only interact with female groups during mating season, which occurs in late November and early December. Lambs are born in the month of May.

While the rams do clash horns, it can be done to establish order, not over the fights to possess ewes. Clashes occur on a regular basis throughout the year, but they become more often before the rut when rams face unknown rams with similar horn sizes.

When food is abundant in summer, the sheep eat a wide range of plants. Their winter diet is more limited and consists mainly of dry, frozen grass and sedge stems available when the snow is blown off, moss, and lichen. Several Dall sheep populations visit mineral licks in spring and often travel several miles to eat soil around the licks.

Primary predators of this sheep include coyotes, wolf packs, grizzly bears, and black bears; golden eagles are the young predators. The Dall sheep have been known to butt the grey wolves off the face of cliffs.

Often, Dall sheep may be observed along the Alaska Seward Highway South of Anchorage, within the Denali National Park and Preserve (created in 1917 to preserve the Dall sheep from overhunting), located at Sheep Mountain in Kluane National Park and Reserve, in Tatshenshini Park Tatshenshini-Alsek Provincial Park in the region of northwestern British Columbia, and near Faro, Yukon.

Range and Habitat

Dall sheep can be found in the Kenai Mountains, Chugach Mountains, Tok area, Nutzotin, Mentasta, northern Wrangell Mountains, Delta Controlled Use Area, west of Delta River, north side of the Alaska Range east of the Nenana River, and south of the Tanana River; Tanana Hills region, in the Central and Eastern Brooks Range, White Mountains area.

Dall sheep prefer the relatively dry terrain and frequent a unique blend of broad meadows, alpine ridges, and steep slopes with severely rough "escape terrain" nearby. For resting and feeding, they go to meadows, ridges, and high hills. They retreat to the crags and rocks to evade pursuit as danger comes. Generally, they are high country animals, but at times, they take place in Alaska in rocky gorges below the timberline.

Status, Trends, and Threats

Status

Generally, the Dall sheep populations in Alaska are considered to be healthy. Typically, the sheep numbers fluctuate irregularly in response to the number of environmental factors. Sheep populations tend to increase in periods of mild weather. After that, sudden population declines can take place as a result of unusually summer drought, deep snow, or other severe weather. Low birth rates, predation (majorly by coyotes, wolves, and golden eagles), and a difficult environment tend to keep the population growth rates of Dall sheep lower than for several other big game species. However, their alpine environment adaptation seems to serve them well.

Sheep surveys are conducted at times of adequate funding, appropriate weather, and staff are available. Sheep are classified into the categories as sub-legal rams (less than full curl); lambs; legal rams (full curl or larger); yearling and ewes rams; and the unidentified sheep. Yearling rams are very difficult to differentiate from ewes and, thus, they are summarized together.

Threats

The sheep's habitat's remoteness and unsuitability for human usage have previously protected Dall sheep from most problems. However, an increasing human population and the more human use of alpine areas can cause future problems for the Dall sheep.

Uses

Dall sheep are valued game animals. In 2007, 916 Dall sheep were harvested in the regions of Alaska that is very close to the five-year average. Dall sheep of Alaska are popular with the nonresident hunters, and the harvest is split fairly evenly between the nonresidents and residents. In 2007, the nonresidents took 403 sheep, while the resident hunters took 513, about 57%.

Dall sheep produce excellent meat, but they are relatively small in size (usually below 150 pounds (68.1 kg) for ewes and below 300 pounds (136 kg) for rams, and meat is difficult to come by in the rocky mountainous places where they live. These restrictions limit sheep hunting to a small number of hardy individuals who value the satisfaction and difficulty of mountain hunting as well as the alpine experience over sustenance.

In August and September, recreational hunting is confined to adult rams. Several recreational hunters are picky, killing only the most attractive rams. Instead, these hunters like to keep an eye on sheep and discuss their surroundings frequently.

Dall Sheep Facts

Let Us Look at Some Dall Sheep Facts.

• Size

Up to 300 pounds

• Distribution

Alpine areas in subarctic mountain ranges of the Alaska region.

• Diet

Herbivorous; sedges, sheep eat grasses, moss, lichen, and other plants.

• Predators

Wolves, golden eagles, coyotes, wolverine, and brown bears.

• Reproduction

Ewes bear a single lamb.

• Remarks

Dall sheep are well-known for their massive, curled horns and the clashes that take place among the males.