A red-shouldered hawk diving for fresh Canada Pond trout. He averaged one catch per three dives, so far as I could see. Considering how expensive hunting must be calorie-wise, I bet he doesn't have much margin for error.
Nikon D300
,Quantaray 70-300mm for Nikon AF 1/1250s f/7.1 at 300.0mm iso500
full exif
That sounds like a good average to me.
I watch Cormorants dive a lot.
Often they will do a dozen dives and catch nothing.
Not unless they are catching very small fish and swallowing them underwater where I cant see them.