Flight is their only real defence against predators.
I had a mallard hen that got it's eye scratched and need some attention, so i clipped her wings so she would be easer to catch, well after that it took months befor her wings grew out and she still did not know she could fly , i watched one day as she was going back to the pond and a hawk flew down at a high speed clipped her behind the head and almost got her as she was tring to get away, i hollered he pulled up and flew off had i not been there she would have been his meal, i had to take her and toss her over the pond a few times untill she relized she could fly again.