The last 2 days I have noted blood on the head area and wounds on the combs of 2 of my hens. While observing them today, my rooster mated/attempted to mate several times with various hens. While he was trying to do his stuff, the hen protested loudly and 2 other hens came and began visciously pecking her on the head. I have never seen this behavior before. Any ideas as to the cause?