Predator mammals - cats, stoats, mink, weasels, fox, badger - tend to eat bones and all. Raptors - buzzards, red kite and so on - often pluck the feathers and pick the bones clean. Rats also pick bones clean. Look for the muck - fox's are like dog muck, except pointed at one end, smaller predators are like smaller versions of dog muck, rats are dark brown cylinders about 2cm long.