My one black chick isn't soft and fluffy like the others. It's feather are more corse and doesn't has as much fluff as the other 5. It also has a lump on the side of its neck. He's always been the runt of the others and now that the others are getting soft and fluffy, it's worrying me. Is there something that could be making this happen? Or maybe an idea of what the lump is?