What they thought of it, we'll never know, because Bird Boy tries to eat a pre-movie advert. This causes general chaos, and then finally Cypher tries to talk to Bird Boy, which he'd previously thought was impossible on account of it being hard. Some progress is made. In #58 the kids try and teach Bird Boy English, which works, after a fashion. Soon he acquires enough English to make simple orders at McBurger's. With the full moon approaching (something he is concerned about - apparently it is the "time of testing"), he flies away to the North Atlantic ("thousands of miles away" from Westchester, apparently, rather than the few km it really is to Long Island Sound), with food for his friends.
Who is he? We still don't know. He's clearly been experimented on, although what or who he was before is another matter. But what matters is he has friends to help, and those New Mutants are going to go with him.
New Mutants #58 has a piece of card bound in, promoting the upcoming launch of Excalibur and the Fall of the Mutants storyline. It also contains a competition, being a slightly creepy "Mutant Registration Form". Fill in your mutant name, send it in with your name and address, and win the prize of appearing in a subsequent issue of New Mutants. Genius.