This is a health issue, that is typically from feeding a bird mostly seeds and table food. If your bird is not eating 80% quality pellets like Harrison's or Roudybush then you need to read our Switching Birds To Pellets article so your bird will be eating a healthy diet.
It would also be a good idea to Find an Avian Vet to examine your bird to make sure there is not something else going on with your bird.