I don't know much about this bird of prey. I usually don't see them until fall, and even then its not too often. The past 3 evenings when I've had my flock out for supervised free ranging I've seen a male northern harrier fly over them. To me it doesn't look like he's paying attention to them, but my rooster begs to differ. They are kept in a secured covered run. I don't let them out if I can't be out with them because the fox are thick in my area and run all hours of the day and night. But I am no help with aerial predators since it seems to take me awhile to see what the flock sees and is screaming about. If NHs are considered a "chicken hawk" species, on lock down they will go.