Do you feed cracked corn daily?
If so stop. By feeding cracked corn daily or often you are taking away from them getting a balanced diet which the 16% layer feed is.
Birds that don't get a balanced diet can become overweight very easily without you even noticing with just your eyes...
Welcome to BYC.
How old is the bird?
What exactly do you feed on a daily basis and when was the last time you brought new to you birds home?
Can you get clear pictures of the bird and fresh poop laid by the bird?