Great Horned Owls in particular have been known to attack poultry, and sometimes if they can't carry off the whole bird they just take off the head. Small meal for the owl, who might kill several in one night, and bad news for the chicken who now has no head.
A hungry GHO will attack anything. I got buzzed by one when I was nine or ten years old because I went out to feed the bunny rabbits who were safely in a hutch, and a GHO fancied the rabbits for himself. The GHO had already made an attempt (and a big dent in the hutch) but the rabbits got safely into their shelter and didn't come out for more than a week. So for a while every time I went to feed the rabbits, I put a thick hood and a peaked cap on, protected my eyes with glasses which I had to wear anyway, and didn't make eye contact.
I know a Great Pyrenees (sp?) dog who successfully mugged and pinned a GHO who was killing turkeys, and who sat on it until the farmer came in the morning. Of course that was an extremely well-trained guard dog, bred from a long line of poultry guardians, whose sole duty in life was to guard chickens and who was trained to do it from puppyhood. Performance like that can't be expected from the average dog.