The tail fluff that is white is the tail coverts and we do not want to breed this forward in any of the males. If you use a male with the cottontail as a breeder you will never breed this FAULT out of your fowl. This certainly can be bred out and will explain how if anyone is interested.The fluff is not desired, but not a reason to cull him from breeding. It can be bred out. Many breeds including Marans and Barnevelders have the tail fluff, you just want to work on it. No bird is perfect, there's always something to work on.