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Wild Sheep Biology

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Rocky Mountain Bighorn Sheep lamb

A group of local bighorn sheep enthusiasts gathered recently at the 2014 annual meeting of the National Bighorn Sheep Interpretive Association. The evening included a ham dinner and a presentation by Greg Anderson, Wyoming Game & Fish Department biologist, about the current status of the Whiskey Mt. bighorn sheep herd. Greg reported that the recent live sheep trapping project garnered results from 22 sheep on Torrey Rim, just outside of Dubois, Wyoming. He gave a BIG Thank You to the many volunteers who assisted with determination in VERY cold weather conditions. Unfortunately, lab results from the samples gathered were not yet available, but Greg will share those with us as soon as they are in hand.

The purpose of the sampling is to identify the primary pathogen(s) responsible for causing pneumonia and particularly catastrophic die-offs in bighorn sheep populations. Although several different strains of bacteria have been detected, ongoing genetic variations in the bacteria makes it difficult to identify the actual culprit. Current research leads to the prime suspect being the leucotoxic positive variety of Mannheimia haemolytica. Quite a bit of effort is being undertaken currently in the halls and labs of the academic research world concerning wild sheep health. We look forward to hearing their results. Thank You to the work of dedicated field biologists like Greg Anderson!

According to Greg, the population of the Whiskey Mt. herd, currently about 900 animals, continues to hold fairly stable, following the trend of the last 5 - 6 years. Although he would like to see population numbers increase slightly, holding steady is good news. The latest lamb recruitment numbers were approximately 25 lambs per 100 ewes, an "okay" rate, but down from a great recruitment rate in 2012 of 40 lambs per 100 ewes. 2013 was considered a poor forage production year at 200 lbs/acre, which may have an effect on this year's lamb production rate, yet to be seen. For a previous article on the trapping and disease testing conducted in 2012, along with some great photos by Mark Gocke, please see this Special Report.

Here's a link to a great article about bighorn sheep that was recently published in the New York Times.

Here's a link to an interesting article about disease testing bighorn sheep near Jackson, Wyoming.

Adult Rocky Mountain Bighorn Sheep Ram

Rocky Mountain Bighorn Sheep, adult ram

Scientific Classification of North American Wild Sheep:

Kingdom:    Animalia
Phylum:    Chordata
Class:    Mammalia
Order:    Artiodactyla
Family:    Bovidae
Genus:    Ovis

Rocky Mountain Bighorn      Ovis canadensis canadensis

The Rocky Mountain Bighorn Sheep is the largest wild sheep inhabitating North America. A large ram (a male sheep) may weigh over 300 pounds and stand over 42 inches tall at the shoulder. They are generally a dark brown to gray/brown color with a white rump patch, muzzle and back of legs. Their coats may appear considerably lighter in spring before the winter coat is shed revealing the darker summer coat beneath. Rams have horns that are massive and tightly curled close to the face. A ewe (a female sheep) will have smaller shorter horns that curve only slightly. Ewes typically weigh 125-150 pounds. Rocky Mountain Bighorns are found in British Columbia and Alberta, Canada and in the western United States south to New Mexico.

Rocky Mountain Bighorn Sheep Ewe and Lamb

Rocky Mountain Bighorn Ewe and Lamb

Other Types of North American Wild Sheep

Desert Bighorn Sheep Ram, ovis canadensis nelsoniGroup of Desert Bighorn Sheep, ovis canadensis nelsoni

Desert Bighorn
Ovis canadensis nelsoni

Desert Bighorn Sheep are generally smaller and lighter colored than their cousins, the Rocky Mountain Bighorn Sheep. A large ram is usually not over 220 pounds. They stand 38-42 inches tall at the shoulder. Desert Bighorns are found in the southwestern United States, including Utah, Nevada, New Mexico, Arizona and southern California. A significant population is also found in northern Mexico. The horns of Desert Bighorns are typically longer and not as massive as those of Rocky Mountain Bighorns. They are usually curled close to the face, but may flare widely outward, showing wide variation in horn structure between individuals. Desert Bighorns also have slightly longer ears and tails than Rocky Mountain Bighorns. Desert Bighorn ewes also typically have longer horns than other North American wild sheep females.

Dall sheep ram, ovis dalli dalli, the wild white thinhorn sheepDall sheep Ewe and Lamb, ovis dalli dalli, wild white thinhorn sheep

Dall Sheep      Ovis dalli dalli

The most striking feature of the Dall Sheep is their nearly all white color. The Dall Sheep is actually a "thinhorn" sheep. Their horns are longer, thinner and yellowish in color when compared to horns of Bighorn Sheep. Their horns also tend to flare outward, away from the face. Ewes horns are usually not over 12 inches long. Dall rams can weigh 225 pounds and stand 40 inches tall at the shoulder. Dall Sheep primarily inhabit Alaska and the Yukon Territory, but are also found in British Columbia and the Northwest Territories.

Stone sheep ram, ovis dalli stonei, wild thinhorn sheep

Stone Sheep      Ovis dalli stonei

The Stone Sheep is a darker subspecies of the Dall Sheep, which also is a thinhorn sheep. Stone Sheep rams can weigh up to 250 pounds and stand 40 inches tall at the shoulder. Ewes typically weigh 30-40% less than the rams and stand 36 inches tall at the shoulder. There are many color phases of Stone Sheep, from an almost black charcoal to light gray/brown and "salt & pepper". They typically have lighter faces, a white rump patch and white on the backs of the legs. Their horns are longer, thinner and more yellow than those of bighorns and tend to flare outward, away from the face like those of Dall Sheep. Stone Sheep are primarily found in southern Yukon Territory and northern British Columbia. In areas where the ranges of Stone Sheep and Dall Sheep may overlap, an intermediate color phase may be found, which is referred to as a "Fannin's Sheep." Technically, an otherwise white sheep with black hairs anywhere except on the tail, is considered a Stone or Fannin's Sheep.

Bighorn Sheep or Mountain Goats?

The Mountain Goat, oreamnos americanus, often confused with white wild sheep

Wild sheep and mountain goats (Oreamnos americanus) are close cousins, both belonging to the Family Bovidae, but they are distinctly different species. To the inexperienced eye, female sheep, especially Dall sheep, may be confused with mountain goats. The most obvious differences between wild sheep and goats are hair color, horn color and structure, and hair length. Mountain goats are creamy-white or yellowish-white, never tan, brown or gray. Both sexes of goats have black horns. When compared to the horns of sheep, their horns are thinner, sharper and swept backward, but not curling. Goats horns average 10" in length. Mountain goats also have longer hair than wild sheep. Especially in winter, the longer hair may form a beard under the chin, and the abruptly ending longer hair on the front legs gives them the appearance of wearing "pantaloons". Goats also have longer, thinner and more sharply pointed ears, often described as pixie-like. Billies (male goats) can reach over 250 pounds and a large nanny (female goat) may weigh 200 pounds.

The ranges of mountain goats and wild sheep may overlap, although goats will usually choose terrain that is even steeper and more precipitous than the favored terrain of sheep. If feeding and bedding areas are challenged, goats are usually more aggressive animals than sheep and will push sheep out of the preferred areas. Mountain goats are found in Canada, Alaska, Washington, Idaho, Oregon and Montana. Small populations found in other states, including Wyoming, exist because of transplantation.

Rocky Mountain Bighorn Ram by Michael P.Flaherty, Rocky Mountain Bighorn Ewe and Lamb by Deb Robinett, Dall Sheep by Jeff Vanuga.