Best tip is keep them on the hungry side . I've noticed last two weeks two hawks doing the rounds one is small and very dark undersides? Seen it being chased by a seagull this morning . My birds been out all winter and I could turn my back when they are flying and turn around and 19 are in and eating . They are well aware of the danger from above.But Iam more than convinced dogs in my garden and dog next doors keep it from attacking.Cats however are a problem I can't get the back of them!!!