Chicken feather condition and what it might mean 

Jason from talkinghens.co... explains some of the reason why chickens might lose their feathers. There are three common causes of feather/plumage loss in chickens and often, it's nothing to be overly worried about.
Firstly, feather loss can occur due to other chickens pecking feathers out to establish the pecking order. Often, they will attack the head and back of the neck along with pecking feathers from the base of the tail, a process known as "silverbacking".
Secondly, chickens around the age of 12-months can often show signs of feather loss due to rubbing their breast bone against feeders and drinkers that they constantly use. This can also happen due to what's called a "pre-moult" where patches of feathers can be lost around the neck to expose clean skin underneath.
Thirdly, a common area of lost feathers is around the behind or Vent of the chicken. This area is favoured by external parasites such as mites and lice and causes the chicken to constantly itch and preen this area to remove the aggravation caused by parasites. The area is warm with good blood flow which encourages parasites to feed and lay their nit eggs in the location.