I think capturing the feeling of thousands of birds flying in formation is a daunting challenge. It could be a bit easier if they were closer and I could use a different lens but they are quite distant most of the time. The compression caused by using a 500mm with a 1.4 teleconverter does add to the feeling of so many birds flying so close together. I always wonder how they don't collide!
I spent a lot of time experimenting with different combinations of camera settings to express what was before me.. Nothing like being there in the mist of it ! Its something that has many interpretations that can be revisited time and time again.