So now I am confused. The D800 manual says: "A Auto FP High-Speed Sync Allows the flash to be used at the highest shutter speed supported by the camera, making it possible to choose the maximum aperture for reduced depth of field even when the subject is backlit in bright sunlight. The information display flash mode indicator shows “FP” when auto FP high-speed sync is active (0185)." So I shoot birds at 1/2000 or whatever, usually with the flash at a reduced output such as -0.5. With a 500mm f4 you clearly need a fast shutter speed and even if there is enough light, you don't want to shoot at f16 because you want to blur the backround. I don't think I have ever shot birds at 1/250th. The shot below was at 1/2000 and f5.6.