2 days ago I noticed that a whole host of my hens started attacking one of my 2 year old hens. My existing flock of 7 hens have been together in a coop for over a year. The hens jump on top of the victim (even the one on the bottom of pecking order), one tries to bite her neck and the others seem to join in. I am wondering if the attackers sense or smell an illness or sickness or virus or some other malady on the victim. 3 months ago I found one hen near death, took her to a bird doctor and had to put her to sleep. The vet wanted to do an autopsy to see if she had some kind of illness. It cost me $72 just to put her asleep, but with a $4 bird, I didn't want to spend the extra money. That's why I think my victim hen has some type of disease or virus. There is something (her smell perhaps) about the victim wherein the others are getting really bad vibes and are attacking. An thoughts? Thank you.