There are over 200 species of owls distributed across all continents except Antarctica. Their relatively large heads, forward-facing eyes, and upright perching posture are familiar characteristics. The fact that each foot has two toes pointing forward and two toes pointing back may not be so well known. Almost all owls are primarily nocturnal, that is, they are most active at night. They primarily eat small birds, mammals, and reptiles and thus are considered "birds of prey." Owls have large eyes and very sensitive ears, which help them hunt at night. Owls cannot move their eyes. Instead, they turn their heads to look around. Some owls, such as Barn Owls, have assymetrical ears and a disk of feathers on their faces that helps them direct and perceive sounds differently in their left and right ears. This enables them to locate the source of sounds more accurately. The ear tufts of some owl species don't seem to be important for hearing; they are just used for visual communication. Most owls have softly-fringed feathers at the ends of their wings that let them fly silently. This helps owls sneak up on their prey.