How do you identify an owl?

There are many kinds of owls, but they all have certain characteristics in common: large, round heads that can turn almost 180 degrees; eyes that face forwards rather than to the side; flat faces with feathers around their eyes that form wide discs or ruffs which channel sound to their ears; small, hooked beaks; strong feet with sharp claws, and generally cryptic plumage in grays, browns, reds and whites. Owls maintain an upright stance when perched.