The paladins make a variety of bird noises.
Keith makes the cutest tiny chirps when he’s happy, and he coos like a dove when he’s content or trying to make someone feel better.
Pidge screeches like a banshee when she’s angry or startled. She scared Allura half to death once when she accidentally startled her. Allura thought she was dying or at least injured.
Lance whistles like a songbird when he’s happy, which is most of the time really, and makes sad little coos when he’s upset. Even if Lance isn’t really that upset, just a little down, hearing it makes Coran want to bundle him in a blanket and ply him with treats and silly stories until he’s happy again.
Hunk chirps and clicks when he’s very focused on a project or cooking, and he squawks like he’s dying if something startles him, which happens a lot. The Galra think it’s some kind of war cry because he’s so loud, and the other paladins think this is hysterical.
Shiro is mostly quiet. His year as a prisoner taught him that, for the most part, being quiet was his best option. His battle cry, though, is terrifying, and even the other paladins are a little intimidated by it on the rare occasions they hear it.
He’s becoming more vocal as he gets used to being around humans again, and he coos to his teammates when they’re upset or stressed. He also will sometimes coo to himself in an attempt to sooth himself when he’s feeling panicked.
Allura and Coran are equal parts fascinated and confused by the sounds they make, and @eastofthemoon had the brilliant idea that they actually think it’s some kind of secret language. When Lance and Pidge realize that’s what they think, they do everything they can to perpetuate the myth, and mange to get away with it for quite a while.
(You can find more of the wing au here.)