Flat Earth: How Discovery Channel faked the alleged curvature of the earth

They had a team conduct an experiment to determine if the earth is round. The helicopter hovered just over the water, disappearing in the distance, which lead them to conclude that there is a curvature.
The only problem is, as the helicopter was descending, a small flock of birds flew by. When the helicopter ascended, the exact same flock pattern was there again.