Hawks will injure and kill large chickens. My neighbor had a red-tail kill one of hers, but they chased it off before it could eat, and a BYC member here in CA lost several chickens to a persistent hawk. Your hawk looks smaller than that, and has a really long tail. Cooper's hawk would be a likely candidate, although not enough detail showing to be sure. I had what I think was a Cooper's (maybe smaller Sharp-shinned) checking out my large fowl last year. It hung out on the fence and in an apple tree for about half an hour before it decided to leave. Might have been an inexperienced youngster. Didn't bother my chickens at all, in fact we only knew it was there because our cockatiel, who has a view of the chicken yard, was screaming bloody murder over that hawk. Resident small hawks fly over frequently, especially during breeding season, and no losses yet, but I worry about my bantams. So far, foxes are a bigger problem for us.
Having trees and bushes that the chickens can hide under helps, and makes them less visible to a flying predator. But a hungry hawk will go to great lengths to make a kill.
