Named for the ram’s large, curved horns, the Rocky Mountain Bighorn Sheep are found scrambling around the cliffs and high hills of the Greater Yellowstone Ecosystem. Females have horns as well, though they’re much smaller and more prong-like. The largest wild sheep in North America, these cousins of domesticated sheep live in large herds, and forage on grasses and small shrubs. Lambs are born in the late springtime, and typically only weigh around nine pounds.
Bighorn sheep rams fight for females (ewes) by clashing heads and their horns together. Rams’ horns can frequently exhibit damage from repeated clashes and they have specialized anatomy that help them to absorb the shock of jarring headbutts.
Males typically weigh 128 – 315 pounds with females 75 – 201 pounds but some Rocky Mountain Bighorn Sheep can weigh up to 500 pounds.
In the winter, bighorn sheep move to lower elevations where possible and graze on windswept south and west-facing slopes like are present on Miller Butte on the National Elk Refuge. Bighorn sheep require trace minerals in their diet for strong immune systems which is why they like to lick the salt from cars. All visitors to the National Elk Refuge are directed to discourage sheep from licking vehicles because they can also ingest other harmful chemicals and salt that imbalances their systems.
As Bighorn Sheep are closely related to domesticated sheep, they can acquire diseases from ranchers’ herds grazing on wild lands. Bighorn Sheep are succeptible to pneumonia and conjunctivitis which can wipe out up to 90% of herds. Conservation efforts work to keep the populations separate, and prevent pathogen transmission.
In addition to threats of overhunting across the state, sheep populations are suffering from loss of habitat and the impacts of climate change. As temperatures warm, water dries up resulting in reduced forage quality for bighorn sheep and affecting the survival rate of lambs.
A small number of bighorn sheep that live in the Teton Mountain Range have had their migration routes cut off causing them to become genetically and physically isolated. Mountain goats introduced to the south have now made their way into the Tetons, bringing disease to this population that doesn’t yet have disease. This could mean local extinction for a small population of just 100 individuals.
Backcountry skiers are also having an impact on the sheep as they are invading critical winter territory at a time when sheep need to conserve valuable calories to survive. There are only 100 bighorns left in the Teton Mountain Range.