Forming into a V
Birds seem as a generality to have great vision. Again as a generality if they spot you, they will be reluctant to fly directly at you or overhead of you (having said this, I did have a merlin zip over my shoulder the other day). Even when shooting birds in flight with big glass, they can veer out of range quickly.
Geese and ducks are a little more predictable on where their flight path will be, whether they are taking off or landing. So you can set up out of sight around a curve, behind a rock, and wait. They will tell you when they are coming!