This is for my dad so sorry for the vague info. he went down to check on the new chickens they are three months old and have been introduced into the flock since Sunday. they have been hiding away from the rest of the chickens. he went down to the coop and seen that most of them were in the coop and when he looked in he saw a chicken laying on the floor this is one of the originals. she was about a year and a half. there is no visible blood or reason why. the only thing we could come up with is that his rooster is very aggressive toward us so maybe him? any help would be appreciated thank you.