Some of my hens are moulting now, generally hens dont moult mid winter but depends on various things and its ot that uncommon. I have kept hens for over 20 years and know for a fact that some of mine are moulting now. Hens will moult when they come to the end of their annual laying cycle and that depends on when they started to lay depending on when they were born. Normally, moulting in adult birds will occur once a year, but it may occur in certain individuals twice in one year, and sometimes only once in a period of two years. We have very mild winters here not having had a frost yet, many years we don't, the last 2 winters were very unusual for us and I'm sure that may delay their moult.