. But found the gizzard and part of intestine about 20 feet away from the
feathers. No sign of any other parts and I've had the dogs thoroughly
investigate

    Here is a possible scenario.  Hawks will hit a bird and if the
surroundings are quiet, start to eat.  We have already come home (when the
dogs are inside.) to a partially eaten bird and as we come in the hawk flies
away.
    Perhaps the hawk or eagle had started to eat your bird, torn open the
insides and was eating when startled.  He may have grabbed the bird in his
talons and as he lifted off and the gizzard and part of the intestines fell
or he could have been eating the bird.  For some reason he liked this part
less and flung them before lifting off with the chicken, perhaps to take it
back to a nest considering the time of year.
Dorothy