It wasn't enough that Birdman already had a sidekick in Avenger. Someone decided he needed a juvenile partner, giving the Solar Sentinel (Keith Andes) his own answer to the likes of Robin, Kid Flash, et al.
Enter Birdboy (Dick Beals), introduced as an semi-amnesiac left all alone at sea, separated from his father, who is presumed lost, thanks to an attack by the Barracuda. Since only one season of Birdman was produced, Birdboy never found his father.
Nearly 35 years later, when the series was resurrected as the satirical Harvey Birdman, Attorney-at-Law, Birdboy was in turn revived as a clerk named Peanut. [Adult Swim]'s handling of the characters over a 6 year period has made it nigh impossible for anyone to properly mount a more appropriate revival of the original series that can finish the story that Hanna-Barbera's staff of writers had created in 1967. Today's audience has been conditioned not to take Birdman & Birdboy seriously. Not only that, but considering that Birdman's own origin was never fully explored, there is a whole wellspring of ideas left unused. That shouldn't be the case, but these are the sort of things that make older fans frustrated with Warner Bros. & Cartoon Network.
Edit: The episode was deleted by YouTube due to copyright issues.