Sudden Chicken Death

[BoysChickens]

First off I am new to chickens and learning as I go.
I had 4 chickens who were doing great for about a year and then about a month ago 3 chickens were eaten by coyotes (they broke into their coop and took them). I only had one left and I felt bad that she was all alone so I went out and got her a few new friends. We built a new very indestructible chicken coop and moved it to our backyard (both yards are fully fenced in). Then a couple of weeks ago she started to loose all her feathers and stopped laying. (I though she was molting since the season is changing. One of the new chickens was also laying and she stopped as well, but no feather loss. Then all of a sudden I noticed that she didn't come out of her coop and she was laying in their all day. So I kept checking on her through out the day offering her water. Then within a few hours noticed that she had died. What might of caused this? I am now concerned about my new chickens. Why would one loose feathesr and not the other? Why would they both stop laying? Please help I'm very concerned about my chickens and do not want this to happen to the other girld.

 

[Ol Grey Mare]

First off I am new to chickens and learning as I go.
I had 4 chickens who were doing great for about a year and then about a month ago 3 chickens were eaten by coyotes (they broke into their coop and took them). I only had one left and I felt bad that she was all alone so I went out and got her a few new friends. We built a new very indestructible chicken coop and moved it to our backyard (both yards are fully fenced in). Then a couple of weeks ago she started to loose all her feathers and stopped laying. (I though she was molting since the season is changing. One of the new chickens was also laying and she stopped as well, but no feather loss. Then all of a sudden I noticed that she didn't come out of her coop and she was laying in their all day. So I kept checking on her through out the day offering her water. Then within a few hours noticed that she had died. What might of caused this? I am now concerned about my new chickens. Why would one loose feathesr and not the other? Why would they both stop laying? Please help I'm very concerned about my chickens and do not want this to happen to the other girld.

Hi and welcome - sorry it is under these circumstances.
When you purchased your new birds did you just go straight to mixing the old bird and new birds or did you keep them quarantined to protect from any illnesses they may have been carrying but not yet showing symptoms of?