Phantom K9 is on to something. Trained crows!
After a red-tailed attacked and killed our drake, a bunch of barn swallows began harassing him until he left the area. I've known red-wing blackbirds to do that, but not swallows. Especially not at nesting time.
Hawks seek targets of opportunity and, if it's migrating, the threat should pass soon enough. Last autumn we lost our smallest duck when a Cooper's hawk killed her. I know our resident bird population pretty well and had seen a Cooper's that morning, in midair pursuit of a songbird, that I...