I remember fly fishing up a small stream, a mama duck upstream from me sent her brood scurrying to hide in the tall grass and then did a loud quacking "broken wing" display, flapping up the current to draw me away. Her problem was that she started at a bend in the stream, her act took her quickly out of sight around the bend. She quickly realized this and stopped her flapping to ride the current back down around the bend to reappear, then started up again as soon as she saw me. I laughed as I watched her do this four or five times, then waded up to the bend to give her a break. Her strategic use of the ruse showed that the behavior wasn't "just instinct".