OMG what is wrong with my hen

[CityCarl]

I have a small flock of 8 hens, today when I went to water them I found blood all over the inside of the coop. It is mixed with poop so someone is bleeding rectally. They have been happy and healthy for almost 2 years, I do not think one is injured or hurt by a predator. One of my golden comets that is normally very active was still on the roosting bar when I showed up at the coop to feed, and normally every one of them freaks out with excitement when I show up to water because they expect scraps or other treats. There was also blood on top of their feed box which is normally where my light brahmas roost. None of them have a bloody rear so it is really hard to tell who is bleeding. One of my rhode island reds is missing a bunch of tail feathers but I think the others peck her a little bit and that has been that way for several weeks, plus I think I am getting close to my first molt. What might be causing all the blood in the coop??? Please Help!