This is probably happening when they relax and preen themselves, not necessarily at night on their roosting perch.
I've had this happen to a rooster who was very docile, and also intimidated by a quartet of very saucy Sussex. They were and still are like a little gang of thugs. Hens like this group together close to the roo, and nibble on his neck or other feathers, saddle feathers being another favorite. I don't understand either why he lets them do it because having feathers yanked out does hurt.The feathers yanked out will grow back, but my rooster's feathers were "chewed" into tatters, and he only was able to grow new ones at the time of fall molt.
Feather picking has a number of causes. You need to figure out if just one culprit is behind this or several. Having only one culprit is easier to deal with. Pinless peepers are invaluable for curing short term behavior problems such as this.
If you have more than one, you might suspect a nutritional cause. Usually improper utilizing of nutrients is responsible and you will have to address that. Recently, I've had great results in curtailing feather picking by feeding fermented feed.
When it comes to curing feather picking, sometimes you just have to throw the kitchen sink at it and hope something ends up working.