Adult Sierra Nevada bighorn sheep are about three feet tall and five feet long. Female sheep are called ewes and can weigh up to 140 pounds. Males, or rams, can weigh up to 220 pounds. Ewes have small, narrow horns, while ram horns are more massive and flare outward in a distinctive curve.
Sierra bighorn come in many different colors, from nearly-white to dark brown, but all have a distinctive white rump with a short dark tail. Sometimes this bull’s-eye rump is the only way to tell whether you’re looking at a sheep or a rock!
The sheep are well-adapted to the treacherous environment in which they make their homes. Their stocky frames and short, strong legs give them remarkable balance as they make their way over steep ledges and talus fields. Sticky pads on the bottoms of their hooves — something like the rubber soles of climbing shoes — help them to grip the rocks underfoot. Their keen eyesight allows them to detect predators at a great distance, and the hollow, kinky hairs of their coats keep them warm even when spending the winter above 12,000 feet.
Bighorn sheep are ruminants, which means their stomachs have four chambers. Like cows, they must chew their food twice in order to digest it. In the Sierra, sheep eat a variety of flowering plants and grasses, choosing the most nutritious forage during each season. Some bighorn migrate to low-elevation habitat to take advantage of lush new plant growth in the early spring. Others stay in the high country year-round, subsisting mainly on the roots of grasses.
Like cows, goats, deer, and their many relatives, bighorn sheep have a stiff pad rather than upper incisors for plucking vegetation, and grind their food between upper and lower teeth further back in the mouth. Counting the number of teeth in the lower jaw can help to determine the age of a sheep. The average lifespan of a Sierra ram is ten to twelve years; ewes can sometimes live as long as twenty years.