You bring up an interesting topic regarding bird photography that I thought of when I saw your photo: blur vs freeze frame. I personally like to "freeze the action", but some "prefer the blur" as it denotes motion..
Any comments from members?
My goal is to get things as sharp as possible. However, I also like to have the birds in flight. That means there is almost always some blur, for two reasons.
The first reason is depth of field. If the bird is in flight, and you're trying to freeze the action, that means a wide aperture. That will create a shallow depth of field. If you look at the above photo, you'll notice that the head is sharp and in focus. Things soften as you move along the wing, and there's really not much you can do about that. I don't exactly photograph them at f 1.4 (Ever tried finding a 600 mm f 1.4?) but still, it's a problem.
The second reason is simple motion blur. Looking at the water drops, you can see I had a fast shutter speed. But he had just snagged a fish and was in full thrust mode to gain altitude. Sometimes you can catch them gliding, and that helps. But in this shot, he's flapping his wings hard, and those feather tips are moving fast. Typically I'd be at 1/800 or so. Ideally over 1/1000th, but if it's cloudy that's not easy.
So, in general? I go for tack sharp, or as close as I can.