Green’s Dictionary of Slang

an effeminate male.

1928		Gleason & Taber Iz Zat So? n.p.: Say, where de ‘ell does he get this..stuff? What does he take us for—a couple of boidies?’ .
1932		J.L. Kuethe ‘Johns Hopkins Jargon’ in AS VII:5 329: birdie—an effeminate man, a pervert.
1949		Monteleone Criminal Sl. (rev. edn).
1965		Guild Dict. Homosexual Terms 4: birdie (n.): An effeminate man, implying homosexual. (Heterosexual, college slang.).
1972		B. Rodgers Queens’ Vernacular.
1987		R. Campbell Alice in La-La Land (1999) 4: The sodomite spoke. ‘You’re a birdie and I’m going to have your ass.’.
1989		H. Rawson Dict. of Invective (1991) 43: Male homosexuals also qualify as birds or birdies, and to go on the bird circuit is to make a tour of gay bars across the [USA].