Our chickens and rooster are about 9months old (born in April 2013) and I noticed about 2weeks ago one of our Golden sexlink girls had feathers missing right behind her comb and then this morning she now has them missing around her wings. The rooster this weekend has them missing around his chest, and one of our barred rocks has them now missing around her comb. A Americana has them missing on her neck and back. We have a total of 8 hens and 1 rooster, is it common for them to start losing feathers in January? All the rest of the girls seem fine, they are all acting normal and havent seen anything out of the ordinary, I have looked for mites/lice and haven't noticed any either. They are eating and drinking. Should I be concerned? Or is there anything i should watch out for?