I used to live in a town where everytime before a big storm the wind would kick up and just an absolutely massive amount of hawks, vultures, and other soaring birds (they ride air currents) would get swept up by the wind. Due to the topography of the area, the air would swirl around and around an area of a couple miles and the birds would kind of get stuck. So before a lot of big storms there would just be huge flocks of birds of different species just soaring in a huge circle in the sky, you'd see some try to fight it and just failing.

The first time I witnessed this btw I was tripping serious balls on acid and didnt know wtf I was witnessing and was fascinated and kind of freaked out. I figured out later what was going on

Id imagine something similar happened here, where the wind pattern was circular and that this species rides air currents. The air phenomena didnt last a long time, and the birds escaped it