Is it my Doberman?
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Chances are a wild animal is eating your hens, some animals leave their kills opossums, raccoons and raptors will leave them out like that. I would say you have a hawk eating them, hawks eat out the front of the birds like their chest, head and any easily eaten muscle mass but leave the extremely boney parts so they can get away quickly.
something like this costs about $15 which is the only other way to know if you don't see it with your own eyes. it records continuously and you can review the last few hours once you see something has happened