I did play around with flash, using a Better Beamer with its fresnel lens to throw light much farther afield. That worked pretty well, too, but I probably prefer the flashless look. Also, as it takes a second or so for the flash to recycle for the next shot, I couldn't shoot in high-speed burst mode. Without flash I could machine gun fire at up to 20 frames a second, offering a much greater chance of capturing a particularly pleasing wing position and overall posture.
Fortunately, cameras are getting much better at dealing with the noise caused by high ISO, and programs like Topaz Denoise do an amazing job in reducing ISO noise in post-processing.