The bird game, Project Q and Saira are all the same game. The game was never officially called Bird Game, we just gave it that name because at first Nifflas hinted that it involved a bird. In the meantime, the bird character was dropped, but Nifflas included a reference to the prototype in Saira and, as Dj Gopher mentioned, kept the sprites to use in the future.
I often speculate to myself that the Bird was associated with the flight powerup, but it is just a guess.
I think the only question that remains to be answered is, in fact, why the name Project Q.