Chicken???

About two or three weeks ago I had a 4 year old chicken die we think it was egg bound at first we thought it was mights but ended up ruling it out cause there was only one or two things that pointed to mites and more things to it being egg bound any ways I have three teenage chickens that are around 3-4 months old that were completely separate from the older one and I woke up to one of them dead I bring them into our garage at night it should have had enough room and it did not look like the other ones attacked it We bring them in cause it gets really cold at night and we have wild animals The main point is I am trying to figure out why it died does anyone have any ideas there did not look like there were any punctures to indicate the chicken being attacked by the other two chicken and it never showed any thing that would make me think it was sick