The Collaborative International Dictionary of English v.0.48:

gaolbird \gaolbird\ n.
   a person serving a prison sentence; a jail bird. [Chiefly
   Brit.]

   Syn: convict, inmate, jailbird, jail bird.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

gaolbird
    n 1: a criminal who has been jailed repeatedly [syn: jail
         bird, jailbird, gaolbird]