I have 4 hens that I got when they were about 33 weeks. Three were together their whole lives and the 4th was added when I took ownership of them. I don't know their breeds (I was told they were mutts). They seem to get along well except this one weird behavior. The three keep 'nibbling' at the 4th's tail. Not pulling out feathers just nibbling at the ends. She doesn't seem to mind but her tail now looks well... nibbled at. Not sure if this is something I should be concerned about. In case it helps: when I got them, all their beaks were clipped. The three nibbling are 2 black and 1 red (brown) the 4th is white. This is their first time with run that's on the ground and I also have a chicken tractor for them to safely roam my yard. I have noticed the 4th chicken's (her name is Early Bird) poop to be runny at times. I have examined her vent and from what I can tell it seems normal. She seems happy. Lays at least every other day. Sorry if this seems like too much info or maybe a little manic. This is my first time owning chickens and I love them dearly (as I'm sure everyone on this website does) so I don't want to make a rookie mistake that may hurt my ladies. Any advice or knowledge would be great! Thanks!