A female (ewe) Bighorn sheep in the Grande Ronde River Canyon, Washington State. Bighorn, or Rocky Mountain, sheep (Ovis canadensis) is a species of sheep in North America and Siberia with large horns. The horns on males (rams) can weigh up to 30 pounds (14 kg), while the sheep themselves weigh up to 500 pounds (230 kg). Two hundred years ago, Bighorn Sheep were widespread throughout the western United States, Canada, and northern Mexico. Some estimates placed their population at higher than 2 million. However, by around 1900, hunting, competition from domesticated sheep, and diseases had decreased the population to only several thousand. A program of reintroductions, natural parks, and reduced hunting, together with a decrease in domesticated sheep near the end of World War II, allowed the Bighorn Sheep to make a comeback.