The turkey vulture (Cathartes aura) and the black vulture (Coragyps atratus) are the common vultures of North America. Known collectively as buzzards, both are large birds, but these two species differ considerably in appearance and habits. Vultures are found throughout North America. Known as scavengers, they provide a valuable ecological service by consuming the carcass of dead animals. This function recycles nutrients and cleans the environment. They make extensive use of thermal air currents to glide for miles across the landscape. They lack a syrinx (vocal organ in birds) and therefore cannot sing or call but make only grunts or low hissing sounds.