Stuart, nice colors and exposure. Image is a bit tight at the top. I do not like the two overlapping birds in the top right corner, and it is a pity that the bird on the left has his wings not fully up. You need to get luck with these type of shots. Maybe you have another in the sequence that you could use to substitute a bird.
I agree with Clemens' critique. I do love the sky/cloud BG, very nice.
The guys were such fun to watch come in and out near the Venice Rookery recently...their whistling and circling tight flights are forever etched in my mind!!
Great shot, and the three birds in a row with increasingly open wing positions make it for me. I'd suggest dropping the brightness a little and maybe upping the saturation some. I think the pink bills and feet should pop a bit more for this species.
I'll be in Texas in mid-April. Maybe I'll get a crack at a shot this nice.