The word "Homo" from "Homo Sapiens" simply comes from the Latin for human. So If humans were birds... they could still be called "Homo Sapiens" because we are still calling them humans. Of course in this world... seagulls would be hominids and gorillas would not.
On the other hand, they could be given some kind of bird genus followed by "sapiens".
For example, I think emperor penguins are Aptenodytes forsteri
If the species is descended from emperor penguins, it could be called Aptenodytes sapiens
If descended from some other kind of bird, substitute the proper genus for that particular bird.