My theory is that Galarian Articuno isn't a real bird. Why? Well, have you ever seen a bird wearing a mask? Exactly. Birds only wear masks when a human puts one on them. Why would Articuno wear a mask if he's a bird? Kantonian Articuno is a bird. Moltres, Zapdos, and their Galarian counterparts are birds. You don't see them wearing any kind of costume or gadget. Now Galarian Articuno, that's not a bird, look at that mask. I think people in the Pokemon universe only agree that Articuno is a bird because he's really strong and would destroy their houses with his eye lasers if they disagreed, but otherwise, they know he isn't one. Zapdos and Moltres also know he isn't a bird but they accept him as a legendary bird because they'd have their asses whopped if they didn't. Anyway, that's just a theory.