Camels can survive for long periods without drinking water. However, when water is available they can drink up to 57 litres at a time to restore normal levels of body fluids. Camels have almost no sweat glands, so they lose water much more slowly than other mammals. Contrary to popular belief, the camel's hump contains fat, not water, and serves as an energy reserve - although the blubber does hold some water. During the breeding season, dominant males defend groups of up to 30 adult females from other males. Younger males form groups of bachelor males.