The birds silhouettes are very striking. My only complaint is you've got a lot of empty space without birds, especially in the lower half of the image. This might be stronger if you had cropped it down to the upper right quarter of the image.
[Edit] I take that back. After looking at some of the other bird shots, the empty space is what really sets the picture apart -- the smallness of the birds against the vastness of the sky. I get it now. Excellent! Bumping up.
I dunno... usually a silhouette makes a much more powerful statement. Here the only subjects in silhouette are so tiny that they don't really matter...