I guess my point is that they’re not “flying” in that they’re not providing thrust. It really is gravity dependent speed with an extremely streamlined form allowing a very high terminal velocity.
I mean, there are other really streamlined animals (aquatic species) that I could probably chuck out of a plane and get similar speeds. Maybe what makes it “flying” is that it’s guided and can be recovered from.
I guess a vulture can be said to be “flying” even if it’s not really providing thrust as much as riding thermals in a situation where their air resistance equally matches their rate of fall.
