If there are no tracks, it may be very difficult to tell. I would say that if there is any plant, or insect matter in it, it is probably NOT bobcat.
Size can be a clue, but how to you tell the difference between a small coyote and a large bobcat? If it is covered it is likely cat.
Cats are not going to eat much in the way of grasshoppers, berries, grapes, or anything with seeds in it.
If it has feathers good chance it is cat.