Adult musk oxen (Ovibos moschatus) near Franklin Bluffs in Alaska, USA, an area named after the British Explorer John Franklin who charted the arctic coastline looking for the Northwest Passage. Musk oxen live in in herds of 10-100 led by one or more dominant males. The musk ox is so called because during the mating season the males give off a distinctive musky odour. Musk oxen feed on birch and willow leaves in summer and feed on mosses and roots in winter. They inhabit Arctic tundra from Alaska, Canada to Greenland. Musk ox herds always defend themselves by forming a defensive circle. The females and young stay within the circle while adult males stay on the outside to fend off predators.