Taking pictures of flying birds can be fun and frustrating. This time I’ll just talk about lighting. Getting them in focus is another matter.
I much prefer the cloudless days for hawk photography. On gray days, the shutter speeds are slower and the hawk does stand out from the sky much.
The first thing I do is take some shots of something in the sun to see what the exposure needs to be. Then I set it all manually. If it’s left on automatic, the camera has too hard of a time figuring out the exposure as the bird gets smaller and larger in the viewfinder, or clouds show up in the background, or it flies low and the landscape is in the background. Better to just figure out the exposure beforehand and set it to that. If the lighting changes during your photo-shooty-toot-toot, then readjust your manual settings. You won’t have time to do that when the bird flies by.
Then, it’s a matter of wandering around looking for hawks. As a bird photographer, you probably know the good spots, which is why you are trying to do it in the first place.
A problem is that the side of the bird that you are shooting is typically facing downwards, away from the sun. If you go out on a winter day with snow on the ground, then the snow reflects a lot of light and really brightens up the bird. I’ve also heard of people going out on a beach, where the light colored sand reflects light. You can also go out earlier or later in the day when the sun is lower on the horizon and catch the hawk as it’s banking away from the sun. All in all, it’s a good idea to be cognizant of the light so that the sky and the bird don’t have too much of an exposure difference.