great, you managed to freeze the flying birds in motion with a sharp focus, but overall, I find the background distracting and undesirable. I guess there's nothing you can do about that cos of the location and your position and maybe the limitation to go shallower in the DOF, but in my sincere opinion, the background spolit these pics a lot, made them look very normal. Maybe next time you can try the stocks enclosure where Darren took his shots, cos that area is more open and it may be easier to get a nice background.
I was using Canon D60 + Sigma 70-200mm (some with 1.4x TC). I also found background disturbing. As birds were quite far from my shooting point and I used 200mm focal length, I could not achieve a smaller DOF. Yes, will consult other experts how to improve bird shots. thx!