Tempest Hawk is a 2/2 flying Bird that allows a deck to contain any number of copies. Whenever one deals combat damage to a player, it can search your library for another Tempest Hawk and put it into your hand.
Bird support such as Empyrean Eagle can strengthen the flock, while cost reduction helps deploy the new Hawks being continually recruited. Thrumming Stone provides the more explosive option of potentially chaining numerous copies together.