So I have been putting a lot of time into my polish birds, and the babies always hatch with HUGE vaulted skulls. I have yet to hatch a chick with a small vault. BUT, they also seem very fragile. Is there such a thing as an overly vaulted skull? Also, how long does it actually take for the skull to harden? I have a few pics below of some brand new chicks I just hatched out. All have the same HUGE vaults.