Probably to steer. Maybe to start resonating the cavity it has.
Discussion
Interesting. Is this the same for all flying animals?
Probably not.. Bumblebee is too heavy for his flying equipment so it puzzles scientists.
This comes from a notion that there is no such thing as gravity on Earth. But that's a whole another rabbit hole :)
I'd agree with no gravity. Everything is frequency, energy, and vibration. Isn't gravity an electromagnetic phenomenon?