From what I have seen, it is unfamiliar noises which scare wildlife. If you flew the same plane over the same nature reserve every day, the birds would get used to it and probably not be bothered. Buy a new plane with a different engine, and for a few days they may get alarmed.
I have seen crows barely more than a rotor diameter from a Chinook starting up, who didn't bother getting out the way, so volume of noise isn't the only factor.
Anyway, who's to say the birds didn't detect a nearby predator which caused them to take flight?
Last edited by Mechta; 25th Nov 2009 at 09:57.
Reason: typo