Photographing Birds in Flight
Color of the Bird
When shooting birds in flight, you need to take into consideration the color of the bird and use the appropriate exposure compensation to account for it. White feathers will become overexposed very easily in bright sunlight. So if a bright bird is brightly lit, I'll under-expose by perhaps 2/3 stop. If I'm shooting a bird with dark feathers, like an immature Bald Eagle, I'll over expose a little, especially if I need to get detail in the shadows under the wings.
Position of the Sun
Direction of Flight
I set my ISO based on the overall brightness of the day. On bright, sunny days, I'll set it between 100 and 250. On cloudy days, I'll set it between 320 and 500. On darker days or early mornings, I'll raise it even higher, but I try not to go more than 800 if I can help it. On newer cameras, you can get away with shooting at higher ISOs, but my goal is to get a shutter speed at least 1/800 sec, and preferably 1/1000 sec or faster. If you find you are getting shutter speeds significantly faster than 1/2000 sec, consider lowering your ISO. You may find that your photos will be less grainy.