If you really want to interest the birds, there's only one thing to do. And that's to sing birdsongs with them. The bird then sees interest in you: you have learned to talk its language and it thinks you're another bird.
"Caw, Caw!" the crow tries to chase anything away from its territory that it feels threatened by. I usually reply to them to arouse their curiosity: "Caw, Caw!"
Not just crows will reply back, however. Mallard Ducks, Magpies, Songbirds, Owls, and other birds will answer when you speak their language. Though they vary in how many quacks or caws they give, they like it if you do the same number they do.