Many many things can cause death in a chicken. But usually they live on and on and on. Right folks? IF your coop and run are predator proof and you supply food and water they will be fine. Please don't let us scare you. I guess we are all trying to give you a peek into the things that we found challenging or "what the heck" moments.
I LOVE my birds. BUT they are birds. They can't hug me or kiss me or even bring me a gift on Mother's Day. I save that love for people. IF one of my birds dies, I get 2 more. (cuz you should never add just one bird to the flock. Now do you see how I got from a planned flock of 6 to a high of 37 and now 27) Now we have talked about the risks of adding adult birds....sooooo I add chicks. Of course I have to raise them in the house if I don't hatch them myself. There is very little risk to your flock if you bring home day old chicks and raise them to fully feathered and then add them to the flock. (better yet, have a hen hatch them for you so you don't have to deal with integration)
Now don't get me wrong, I cried the first time I had to kill a chick that just wasn't going to make it and couldn't get to the food and water. I kept saying "I'm so sorry, I'm so sorry", crying as I killed it, wrapped it in a bag and dug a hole to bury it. (I don't bury them any more....they go to the dump. So I guess you do get used to the loss) The first time I found a chick squished by a non-mother hen I cried and kept it in my hand hoping it wasn't really dead. The last time I found a dead chick I put it in the egg basket and threw it in the basket when I got to the house. You get to where it bothers you, but only until it is out of sight.
A wise old farmer told someone that "if you're gonna keep livestock, you're gonna have dead stock". (One of my birds ran across the yard and dropped dead. Heart attack. And he looked so healthy. LOL)
I don't think you will find anyone on here that hasn't lost their favorite bird, their only rooster or had birds just dissappear off the face of the planet. The kids usually handle it better than the adults, cuz kids just think "we'll get another one"....so take that attitude....we'll get another one or two or three....and the pain of loss goes away pretty quickly. (did we meantion "Build BIG"?? LOL)