Birds. Consider real, living birds—not Alfred Hitchcock's movie Birds or the Birdland Jazz Club or the English band The Yardbirds. How do we recognize birds? We see them in flight. We see them perching on branches and telephone wires. We hear them chirping and singing. We hear the flapping of wings as a flock turns in the sky. We also recognize birds indirectly: a nest of twigs tucked into an evergreen shrub; a pile of feathers on the porch (evidence of a cat's recent meal); and bird droppings on a car parked too long under a tree.