Eastern Screech Owls (Megascops asio)—the type found on the East Coast—and Western Screech Owls (Megascops kennicottii) look alike—so much so that DNA analysis or the birds' songs are necessary to tell them apart.
Normally, screech owls neither hoot nor screech—instead they have a trill for their typical territorial call, with four individual calls per second, voiced one after the other (although the sound does not resemble screeching or screaming). They also have a kind of "song" which is used in courtship and, as a duet, between members of a pair. Calls differ widely between species in type and pitch, and in the field are often the first indication of these birds' presence, as well as the most reliable means to distinguish between species. The distinctness of many species of screech-owls was first realized when vastly differing calls of externally similar birds from adjacent regions were noted.
Screech owls come in gray or red (rofous) polymorphic morph
The common name "screech owl" is sometimes used for the not closely related Barn Owl as well.
Injured Red Morph
Vocalization of the western screech owl