Vultures are scavenger birds which feed on the carcasses of large animals and search out their food by flying in circles at a height. Hovering at a height gives them the advantage of surveying a large area. This is because the effective area which they can survey is the base of a cone at the tip of which the birds fly. Greater the height of this cone, larger is the area of the base. Thus, birds flying in small circles at great heights can keep a watch on a large tract of land below to look for a meal. That is why vultures and other birds of prey like kites, hawks and raptors circle at great heights. Of course, picking up tiny animals from such distances requires sharp eyesight, which all these predatory birds have.