Yes, opportunistic. They do not bother mine because they are big girls and would woop a crows butt. I would worry about little ones but my "yunguns" are in completely covered grow out pens. I don't have Bantams: even though I somehow keep getting eggs for them....even a show girl and some slikies somehow made it into my incubator.....I have watched crows and ravens hunt squirrels and they will happily take a chick. They are not hunters, but they will grab what they can.
Hawks are something I do worry about. I also worry about the Blue Marans that roosts on the roof at night. Has anyone had one of those big white Owls get a chicken? I see one fly over every once in a while.