I don't think it'd be a dog, the chickens are in a large fenced area (52"h livestock panels, narrow spaces at the bottom), they share it with a couple of ducks, two goats and a mini donkey. The area is right behind the house too.
Something killed Rita, a sweet older hen between 2 and 4 in the afternoon. She seemed to be partially skinned with the skin pulled up from her back almost over her head and her tail was pulled off. Since that happened I spoke with a friend whose neighbor lost a few chickens in the same manner...