Green’s Dictionary of Slang

a narcotic drug abuser, a heroin addict.

1991		D. Simon Homicide (1993) 247: [...] putting the handcuffs on the most mindless shitbirds.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 91: Wicked Wendell [...] a rape-o/a shitbird/a heel.
2001		N. Green Shooting Dr. Jack (2002) 220: ‘That’ll be the day,’ the black one growled at him, ‘I let these shitbirds dictate where I can go.’.
2012		M. McBride Frank Sinatra in a Blender [ebook] What do I look like, shitbird? I don’t known nothin’ about whatever it is you think I know.