Good light and good exposure, so you're on the right start there. 8) As for making a stronger image in the future:
1. When shooting the more common biirds, like these, gulls, duck, etc, keep an eye for behavior/environment that stands out from the norm
2. In these situations, get in tighter. Especially when you have the focal length to do it. Between the patterning on the left-most bird itself, and the reflections from the waves, this would have been an excellent candidate for getting "in its face" with that 600 and really highlighting those features.
3. Get the subject away from being so much dead center in your frame; in this instance, having all of them but your flapper in particular, down and right a bit. More toward that lower, right corner. Personally, I try to get the eyes/bills fairly close to one of the "power points". These points being the imaginary intersection of the lines if you divide the frame into 3rds, horizontally and vertically.
4. Make sure you get focus on the eye(s) and give a direct line of eye contact to your subject from the viewer's POV
5. Get your water straight; having the water surface tilted to the side like this sort of leaves the viewer tilting their head to view the shot a bit.
6. Much like photographing children or anyone significantly shorter than you, try to get as low as you can to get on "eye level" with the birds whenever possible.
A lot of your interest will come from the details in the birds, especially when you're shooting static subjects. So, catching some sort of action behavior, like feeding, bathing, etc can really help.
Most of all, keep practicing as you already know from the rest of your photography 