Creature Feature Friday: Bighorn Sheep of GYE

Welcome back to Creature Feature Friday, where we spotlight one of Yellowstone's wild and wonderful residents, brought to life by the striking photography of Julia Cook. This week, we scale the steep cliffs and rugged canyons of the Greater Yellowstone ecosystem to get a closer look at one of the park's most striking and agile animals: the bighorn sheep.

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#1 Those Horns Are Heavy—and Important

The massive curved horns of male bighorn sheep (rams) are one of the most recognizable features in the animal kingdom. These horns can weigh up to 40 pounds, accounting for more than 10% of the ram's total body weight. Composed of a bony core and a keratin sheath, the horns are also filled with blood vessels that help regulate body temperature. Unlike antlers, bighorn horns are never shed and continue growing throughout the sheep's life. Female bighorn sheep (ewes) have smaller, straighter horns that grow much more slowly.

Horn size isn’t just for show—it’s a key part of social structure. Rams with the largest horns often dominate mating hierarchies. During autumn, rams participate in dramatic headbutting contests, charging at each other at speeds of up to 20 mph. These battles can last for hours and are made possible by the rams' reinforced skulls, which include extra bone layers to absorb impact.

#2 Cliffside Champions

Bighorn sheep are true mountaineers. Their specialized, rubbery hooves and excellent balance make them adept at scaling rocky terrain, steep ledges, and craggy slopes. In Yellowstone, they are often spotted on the cliffs of Mount Washburn, Gardner Canyon, and the Calcite Springs area.

Lambs are typically born in May or June on high, inaccessible cliffs to avoid predators. At birth, they are covered in a soft, woolly coat and already have tiny horn buds. Though able to stand and climb within a day, lambs stay hidden for about a week before beginning to follow their mothers. Males leave their mothers and join bachelor groups at 2 to 4 years old, while females often remain in their maternal herds for life.

#3 Survival and Struggles

While bighorn sheep have adapted impressively to life in rugged environments, their populations are still vulnerable. Yellowstone's northern range is home to 10 to 13 interbreeding bands, with a total population of around 345 sheep as of 2018, including 131 within park boundaries.

Disease, especially pinkeye (keratoconjunctivitis) and pneumonia, has historically caused significant declines. A 1982 outbreak of pinkeye reduced one herd by 60%, and a pneumonia event in 2015 led to further declines. Because these diseases impair vision or breathing, they can be fatal for animals living in such treacherous terrain.

Bighorn sheep also face competition from elk and nonnative mountain goats for food and habitat. Human disturbances, habitat fragmentation, and climate change add to the challenges. Conservation groups and wildlife agencies continue to monitor and manage the population to maintain genetic diversity and long-term stability.

#4 Behavior and Lifespan

Male bighorn sheep typically weigh 175 to 300 pounds, while females range from 75 to 200 pounds. Rams live an average of 9 to 12 years, and ewes can live 10 to 14 years. Mating season begins in November, and horn growth is most rapid during early life and summer months.

Elder rams often have "broomed" horns—tips broken off from years of sparring. Within herds, horn size impacts not only reproductive opportunities but also social dynamics. Lambs are weaned around 5 months of age, and females usually give birth to a single lamb each year.

#5 A Yellowstone Icon

Though once more numerous, bighorn sheep now exist in fragmented populations across the Rockies, making Yellowstone's herds all the more precious. They are a favorite among wildlife watchers and photographers for their stunning appearance and cliffside agility. From steep winter ranges to summer meadows, these agile animals are a living reminder of the wild and untamed character of the West.

Thanks for joining us for this week’s Creature Feature Friday! Check back next week as we continue our journey through Yellowstone’s wildest wonders—one species at a time.

Visit Julia Cook's Website to view her other amazing work!