I agree, sometimes chickens do it when they are bored. Some chickens also would peck at beards and crests out of curiosity. Beard pecking may also be caused by food getting stuck in the beard.That's not always the case though, I have a brahma that "grooms" my EEs beards - apparently she doesn't think they should have beards since the rest of the chickens in the flock don't. My chickens are on 20% flock maker.
Sometimes observing our chickens makes a big difference as far as the behavior they exhibit.