My dad and I started out with 10 chickens about 3 months ago (they were a month old when we got them) and now there are four left. One of them died because it got sick when it was young. The other five we just found in the cage on the ground. The first one to die was torn to pieces. None of the others acted sick before they died or had any wounds. What is wrong with them? Could there be a snake in the cage or something poisonous?