'Untamed Americas': 24 of America’s Wildest Creatures

Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis)
U.S. and Canadian Rocky Mountains

Bighorn males use head-to-head combat to exert dominance. They'll butt horns -- which can weigh 30 pounds -- for up to 20 hours until one ram accepts defeat.

Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis)
U.S. and Canadian Rocky Mountains

Bighorn males use head-to-head combat to exert dominance. They'll butt horns -- which can weigh 30 pounds -- for up to 20 hours until one ram accepts defeat.