Why do birds float? Petition to exterminate floating birds.

[Vesperia]

Birds going extinct for no reason? Yeah good luck with that one.

"insert trololololol"

This is an unpaid beta test. SE doesn't have to give lore-justifications before they fix bugs.

And if they did, then by that token they would have to explain the upcoming battle changes. Try explaining the imminent release of auto-attack. What? - so now we're all suddenly automatons from Windurst? Um, wrong game S.E.!

Besides, here's a reason:

The birds, being so opposed to gravity as they were, eventually found themselves floating off into the heavens. This mass exodus of befouling fowls was met with nothing but rejoicing sounds all over Eorzea as people ran into the streets in their jubilation, crying with delight as the birds ascended to their perch in the skies, never to besmirch the landscapes of FFXIV again.