Could be a dog, i have to rule out the hawks since it was done during the night. It could be a Owl as well there are four Owls that can kill your chickens in AZ. Barn Owl, Western Screech-Owl, Great Horned-Owl and the Spotted Owl wich is endangered, they all hunt on small mammals, rodents and birds.So, it doesn't sound like they were eaten at all? If that's so, I would suspect a dog.