with their acute eyesight and hearing, ostriches can sense predators such as lions from far away. when being pursued by a predator, they have been known to reach speeds in excess of , and can maintain a steady speed of , which makes the ostrich the world's fastest two-legged animal. when lying down and hiding from predators, the birds lay their heads and necks flat on the ground, making them appear as a mound of earth from a distance. this even works for the males, as they hold their wings and tail low so that the heat haze of the hot, dry air that often occurs in their habitat aids in making them appear as a nondescript dark lump.