I've got five 3-month old hens and am noticing a lot of feathers on the ground and in the henhouse. Maybe a couple dozen, maybe a little more. I spend a lot of time observing them every day and I never see them pecking at each other. I can tell from the feathers that they're from all the birds, not just one, although one of them is shedding more than the others. Is this normal? If not, what might be causing it?