I have no idea, but mine are 9 weeks (10 tomorrow) and for the last couple weeks a couple of them love to pick at my hair (still attached to my head) when sitting on my shoulders. They aren't pulling it or swallowing it at least, and I do discourage it. The answer for me would be to stop letting them sit on my shoulders...perhaps it is something a smart hen would teach them, but hopefully they will figure out it is not good and stop. And then teach new littles that if they are allowed to brood.