Too many Foxes here ,I snuck up on some in the yard then took a photo just before they all bolted off in different directions.
Always dead possums in my yard ,the fox kills more than it can eat and just leaves them to rot, same if you had chickens doesn't kill one or two for a meal ,Foxes will kill them all and probably eat one.
I think if I had my own Chickens I would tell the difference in the eggs AVB ,I have heard it's difficult to tell the difference especially if free range can just mean that the chicken had a small patch of grass for part of it's life .