Green’s Dictionary of Slang

(US teen) a fool, an eccentric.

1956		H. Ellison ‘I’ll Bet You a Death’ in Deadly Streets (1983) 41: That goony-bird Vode’s been in the way.
1961		(con. early 1950s) J. Peacock Valhalla 179: This peacetime is for goonie birds. I’ll take Ko-rea any day.
2006		C. Hiaasen Nature Girl 285: What are you goony birds talkin’ about?