Several years ago I was in a blind with a good friend and we had seen a pretty steady stream of ducks....pretty good hunt and we were getting close to our limits. We hunted not to far from a small regional airport so it was not uncommon to see or hear a small Cesna tooting around. We noticed and commented that all of a sudden the flow of ducks stopped and didn't even see anything hitting other water. They just stopped.
Looked to the north and saw what appeared to be a small plane flying our way but something didn't seem quite right. As it got closer and topped the trees a few hundred yards to our north we both stood up and put our guns down. Neither of us said a word...just stood and watched in awe as a bald eagle swooped down to our decoy spread to get breakfast. Smart bird cause as it reached to grab a decoy it realized he had been fooled and with one flap of his wings he departed. We stood with our mouths opened and our hands over our hearts.
Moral of the story is that I have no idea whether a turkey vulture will affect ducks....but a bald eagle will!