Flying Ducks

Three flying drake mallard ducks in a rapid descent with wings cupped. I spend many hours (days!) trying to get shots like this. These are coming in to a landing but the airspeed is still wicked fast. Also, they don't track in a straight line but, instead, will often bank quickly to one side or the other. These three are with a hen that already side-slipped out of my frame on the right side. Very difficult for the tracking focus to lock on and keep up with the rapidly changing distance. When the ducks get closer to the water they will slow their speed but they also start backpedaling with the wings so we don't see the wings cupped like this.

I hand-hold the camera and it moves a great deal when I'm shooting like this. With the lens at 400mm I compensate by using a fast shutter speed, usually 1/1250 sec. This image is nice and sharp. But the main problem is getting the focus to lock on.