The Mountain Goat (Oreamnos americanus), also known as the Rocky Mountain Goat, is a large-hoofed mammal found only in North America. Despite its name, it is not a true goat, as it belongs to a different genus. It resides at high elevations and is a sure-footed climber, often resting on rocky cliffs that predators cannot reach. Both male and female mountain goats have beards, short tails, long black horns, 15-28 cm in length, which contain yearly growth rings. They are protected from the elements by their woolly white double coats. The fine, dense wool of their undercoats is covered by an outer layer of longer, hollow hairs. In spring, mountain goats moult by rubbing against rocks and trees, with the adult billies (males) shedding their extra wool first and the pregnant nannies (females) shedding last. In the winter, their coats help them to withstand temperatures as low as -50 Fahrenheit (-46 Celsius) and winds of up to 100 mph (161 km/h). A billy stands about one meter (3'3") at the shoulder to the waist. Male goats also have longer horns and a longer beard than nannies. Mountain goats typically weigh between 45 and 136 kg (100 - 300 lb.); females are usually 10-30% lighter than males. The mountain goat's feet are well-suited for climbing steep, rocky slopes, sometimes with pitches of 60 degrees or more, with inner pads that provide traction and cloven hooves that can be spread apart as needed. Dewclaws on the back of their feet also help to keep them from slipping.