Silkie loss of feathers

[silkie3190]

Hi have 4 silkie hens and 2 Roos I attached a pic two of my hens have lost feathers right below wigs on their backs can some tell me what that could be

 

[tinakevin]

Possibly over mating. With 2 Roos U should have more hens. I had a barred rock with 6 hens and he still over mated with 2 of mine. I ended up putting an apron on them then getting rid of him so they could heal.