Thank you for the suggestions. The coop is very secure and we live in Pennsylvania, so it isn't warm here yet. I tried keeping them all in the coop for three days straight and then they went back to roosting in the bush at night as soon as I let them out. Sigh. I just want to get this fixed...
So I had 9 chickens that I have had for about 2 years. Previously, they free ranged my yard all day then at dusk headed back to the coop where they roosted for the night. Every single day like clockwork. Last month, we lost two chickens, we are not positive what happened , but have a feeling...