I just used the natural light that was seeping over the mountains before sunrise. There were so many birds that it overwhelms the eye sometimes. By silhouetting them you could see their unique shape and see the numbers and not be overwhelmed by all of the feather details.
I shot this using a Nikon D70 camera with a Nikkor 80-400mm zoom lens set at 110mm. I used a "The POD" bean bag resting on the observation tower rail for tripod. The Nikon D70 settings were 1/750 sec at f/16 with an ISO of 1600.
I was impressed with how many birds there were flying all at the same time and in the same space with no mid-air collisions. It was like they had a "built-in" avoidance radar similar to the kind that automobile designers are spending lots of time and money putting in cars and these birds had been born with it.