Just found out a bug: in stage 6 (maybe in others too) you can just walk to the left from the beginning and go around the borders of the map. Also enemies won't be able to shoot you. Very useful if you're doing a speedrun or using the hardcore device.
If you want to beat this game in no time, the best trick is to do short and fast movements of your mouse to the left and right. This will make your flock fly in a tighter formation, thus allowing you to sneak between most aircraft. It will at the very least make you lose a couple less birds, sometimes none at all. Trust me, I had to kill myself after 366 seconds to get the 25 plays achivement.
 "Mechanical Commando 2"){kind=icon}
 "Endless Migration"){kind=icon}