I had the dog kill the 25 chickens , no blood , all from one dog within a hour. I let them out to ffree range ,then went to town and back within a hour, dog ran off, he had kill over 25 of my 50 cornish cross (grown). Looked like piles of snow all over the yard, in the summer....just wet none ripped up.
My money is on the dog, heck it even had one in its mouth. No way would a chicken survive a bear attack, Dog kill for the fun, so you would find just feathers or whole bodies. Even like one still alive, but just been carried off. Dog would also hide them.
Would think the bear would eat them there, so should find some body parts. Plus even in grass area a heavy bear would leave some tracks, near where the feathers are. Sure that track is a black bear, but how far from the kill area????
Now a great horn owl would carry them away, leaving only feathers. Look on roofs of building for signs of a kill.(they like to eat off the ground) They will take , up to about 3 a night.
Still think the dog was still carring around one, that he kill, as his new toy.