If its flapping its wings then you probably have more then one sprite.
Which is a challenge. Im pretty sure there are easier methods but what i do is I put all the sprites I dont need 300 feet above the stage. In the animation I make mabye one of them last for about 20 frames, then shoot that one up to 300 feet at frame 21. Then I take another frame thats up at 300 feet and put it down at frame 21. So really your switching out sprites in mere like nanoseconds. Giving the illusion of animations.
Why do you do that? If you have unused sprites why not just keep them out of the thing then?
I might be piggy-backing off this thread as I had a thread asking how to animate stages as well, but Mewtwo2000 confused me and scared me away.