The horns of a male Marco Polo sheep can reach up to 190 centimetres from tip to tip — longer than a tall adult human is tall. The horns grow throughout the animal's life, adding a new ring each year rather like the rings inside a tree trunk. Scientists can count the rings to estimate a sheep's age. Females have much shorter, straighter horns.
Marco Polo sheep live in herds on high open grasslands called alpine meadows, at altitudes between 3,600 and 5,200 metres. The air up there is thin and cold, but the sheep have thick woolly coats and can travel many kilometres a day in search of the hardy grasses that survive at such heights. In winter, they move down to slightly lower, sheltered valleys to find food under the snow.
These sheep are powerful and agile despite their size. An adult male can weigh as much as 185 kilograms — heavier than two average adults. When two males compete, they rear up on their hind legs and clash their enormous horns together with a crack that echoes across the mountains. The winner earns the right to lead the herd to the best grazing spots.