The most common cause of feather loss is the annual molt. This normally occurs when the birds are around 1 year old and may take several months to complete.
It is natural for egg production to be lower than normal during the molt, and it should pick back up again after the molt. The molt usually starts with the head then moves to the neck, chest, back and wings. A rooster will lose feathers around his neck and back.
Another cause of feather loss can be nutritional deficiency. Check that the birds have access to the appropriate feed for their stage of development. Check, too, that the feeder is not overcrowded. As your birds mature, your chick feeder may not have enough space for the now older, and larger, birds.