Green’s Dictionary of Slang

birdie n.2

[bird n.1 (1d); note 14C–16C SE bird, a young man]

an effeminate male.

[US]J.L. Kuethe ‘Johns Hopkins Jargon’ in AS VII:5 329: birdie—an effeminate man, a pervert.
[US]Monteleone Criminal Sl. (rev. edn).
[US]Guild Dict. Homosexual Terms 4: birdie (n.): An effeminate man, implying homosexual. (Heterosexual, college slang.).
[US]B. Rodgers Queens’ Vernacular.
[US]R. Campbell Alice in La-La Land (1999) 4: The sodomite spoke. ‘You’re a birdie and I’m going to have your ass.’.
[US]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].