Are there other instances where JRRT employed avian spies?

In both the book, and the movie, the Fellowship sees a dark cloud approaching before Legolas's keen eyes see the cloud is really a flock of birds likely spying for Saruman and the Fellowship hides until they fly by. Considering an Elf could see them before they could see him, I have to wonder just how useful Saruman's avian spies really were. Are there other instances (beyond this flock and the Bard's thrush) where JRRT employed avian spies in middle-earth?