How are a large number of shots tracking the flight of birds taken in Migratory Birds?

I have seen the recording of Migratory Birds. Those videos that are very close to the bird itself, keep pace with the speed of the bird and have a good angle are all taken on light gliders. Gliding wing aircraft can keep a low speed similar to that of birds and make less noise. But even so, the sound of propellers and the size of airplanes are hard to keep wild birds natural.

Therefore, many birds in the filming of Migratory Birds are artificially cultivated. They have been in contact with gliders since childhood and have flown and followed them many times. Only when the glider is no stranger to them and does not affect them can they shoot smoothly.

In documentary shooting, in order to keep a low speed, light propeller planes are basically used, and sometimes hot air balloons are used.