Impossible Image: Gravity-Defying Bighorn Sheep

Bighorn sheep can climb slopes that would make Spider-Man shake his head. The above image doesn't seem possible, but it's no April Fools' Day joke; for these climbing pros, it's just another day on the mountain.

Bighorn sheep get their name from their big, curved horns on the males, which are called rams. But it's their climbing skills that turn heads. Bighorn sheep aren't as agile as mountain goats, but they are well-equipped for climbing the steep terrain that their predators can't.

Bighorn sheep's sure-footed climbing skills are due to their feet, which are perfect for climbing unbelievably steep and rocky slopes. Modified toenails on bighorns' outer hooves are shaped to snag any slight protrusion on a rocky surface. A soft inner pad provides a grip that rivals the best climbing shoe in its ability to handle slight changes in the surface of a cliff. Within a day, a lamb can walk and climb as well as its mother.

A bighorn sheep's size makes its climbing even more impressive. Bighorn sheep can weigh up to 300 pounds (136 kilograms), with the horns adding another 30 pounds (13 kg). In the winter, bighorn sheep live between 2,500 to 5,000 feet (760 to 1,500 meters) in elevation. In the summer they climb even higher up to 8,500 feet (2,590 m). Their climbing skills help them evade predators such as coyotes and bobcats. Few predators will follow them to such heights.

To see a bighorn sheep in action, head to the Rocky Mountains or the Sierra Nevada mountain range. Desert bighorn sheep can be found from the southwestern United States into Mexico.

Editor's note: This story was corrected to reflect the correct identification of the animal in the photo as a bighorn sheep and not a mountain goat.

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