I have seen a pile of downy light feathers in the Inch Lake Wildfowl Reserve, (no other traces of hunter or hunted) where there are several raptor species, but I'm not sure if the hunter was a fox, or what species the poor bird was. I would imagine them more susceptible to ground-dwelling predators, but not exactly targeted by birds of prey- any flying bird would be obvious for species that tackle their prey mid-flight. Perched birds would be a different story, if anyone else knowns anything?