Monday, June 22, 2015


Bighorn sheep have really big horns, and that is how they got their name.  The horns of a ram can weigh as much as 30 pounds, which is about the same weight as 5 or 6 chihuahuas, all snuggled up together.  Bighorn ewes also have horns, but theirs are shorter and not as curly.  Coat colors range from light brown to dark, chocolate brown.  The rump and linings on all 4 legs are white.  Males usually weigh between 127 and 316 pounds.  Females weigh from 75 to 188 pounds.

Bighorn sheep are described as native to North America, but their ancestors came here by crossing the Bering land bridge from Siberia during the Pleistocene Era, about 750,000 years ago.  The Siberian branch of the family has since died out.

At one time, the population of bighorns was over two million, but by 1900, there were only a few thousand sheep left.  Mostly this was because of diseases such as pneumonia and scabies introduced from European livestock, and also because of overhunting.  More recently, the bighorn population has been restored through the efforts of several conservation groups, along with the Boy Scouts of Arizona.

Dall Sheep

There are two extant species of wild sheep in America today.  Dall sheep (Ovis dalli) live in Alaska and northwest Canada, and bighorn sheep (Ovis canadensis) range from southern Canada to Mexico. The two species are not so distinct from each other anymore because they sometimes interbreed.

Desert bighorn sheep in Hellhole Canyon,
Anza-Borrego Desert State Park
Photo by Andrew Barna

Desert bighorns live in the hot, arid ecosystems of the Southwest.  Rocky Mountain bighorns have a habitat that consists of alpine meadows, grassy slopes, and rocky cliffs and bluffs.  In summer, these bighorns move high up into the mountains, but they spend the winter in lower elevations.  They eat grasses and shrubs, and they get minerals from natural salt licks.

Bighorns are very good at navigating steep, rugged terrain.  They are usually safer from predators in such places, although cougars are also good at climbing over rocks and cliffs in pursuit of some tasty mutton.  Other predators of adult bighorns include bears and wolves.  Lambs are often hunted by coyotes, bobcats, lynxes, and golden eagles.

Bighorns in Glacier Park, photo by Kim Keating

Bighorn sheep live in large herds, but there is usually no single leader ram.  However, before the mating season (the "rut") begins in the fall, the males start fighting to determine which rams get to mate which ewes.

The fighting is very dramatic, with lots of running at each other and slamming their heads together.  Luckily, rams have large horn cores plus enlarged frontal sinuses and a bony head structure that makes it possible to survive all that head butting without getting brain injuries.

Bighorn lamb, Alberta
Photo by Phillipp Haupt

The peak of the rut is generally in November.  Then, six months after mating, a ewe's lamb is born.  In rare cases, she has two lambs.  Newborns weigh between 8 and 10 pounds, and they can walk within hours.  Lambs born earlier in the season have a better chance of surviving than later lambs because their mothers have access to better forage while producing milk.  Lambs are weaned when they are 4-6 months old.

Bighorn sheep were particularly admired by the Apsaalooka (Crow) people.  The Bighorn Mountain Range was central to Apsaalooka tribal lands.  In the Southwest, ancient peoples depicted bighorns in many of their petroglyphs.

Today the Rocky Mountain bighorn sheep is honored as the provincial mammal of Alberta and the state animal of Colorado.

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