Bactrians live in the Gobi steppe along rivers and move into the desert as soon as the snow melts. They can stand extreme heat and cold and are good swimmers. They can travel carrying 375 to 600 pounds at 3 or 4 miles per hour for 4 or more days. Their urine is concentrated, and their dung is so dry it can be used as fuel as soon as deposited. They can store up to 80 pounds of fat in the hump. The hump shrinks as this fat is used. Food is not chewed completely before swallowing. They bring up partly digested food, called cud, and chew it, then swallow it again. Their mouths are tough enough that they eat the thorniest plants without injury. They can drink brackish water if they have to, and will eat fish when hungry enough. They can drink as much as 30 gallons of water in ten minutes. Camels live in groups of up to 30. When rival males meet, they display by urinating, defecating, tail slapping, and spreading hind legs. If these measures are ineffective, mortal combat may ensue. Camels have no enemies.