Green’s Dictionary of Slang

dirty bird n.²

an unappealing individual.

1960, 1975		Wentworth & Flexner DAS 150/1: dirty bird A so-and-so.
1987		S. King Misery (1988) 230: He was nothing but a hippie dope-fiend dirty bird. [Ibid.] 231: The dirty birdies round here would say anything to get me in trouble.

In exclamations

I’ll be a dirty bird!

(US) a mild excl.

1970

(con. 1950s) H. Junker ‘The Fifties’ in Eisen Age of Rock 2 (1970) 100: Well, I’ll be a dirty bird.