A song bird is an entirely white bird known for its disctinct voice, "singing," during the breeding season. A song bird is different than any other bird because it is the females who looked for their mates and sing the tunes that make the males fly for miles to mate. For the urbanites, A song bird is any hot chick whose slightest whisper can make guys go berserk to get a glimpse of her.
Dude 1: Dude! She's laughing.
Dude 2: Who?
Dude 1: The girl next door
Dude 2: WTF! You can hear her from here?
Dude 1: She's a song bird