Well, seeing how they are part bird, and there are various blue birds ( Kingfisher, Bluejay, Blue Tit, Great Tit, the Bluebird, Blue Tanagar etc. ) this might not be that surprising. Of course there are no blue birds of prey, but I don't think he is meant to be one, similar to Gabby who is based on a pidgeon, as opposed to Gilda ( Bald Eagle ) or Gruff ( Vulture ).