The sun silhouettes the birds from the flight deck in the morning. Try to trigger the shutter release to occur when the background has the most interesting color. Often small groups of geese move about before the flock departs, and this will give you some opportunities for individual photographs as well. Exposure can be tricky, but your meter will always give a silhouette when confronted with an extremely bright background. This is a situation for bracketing as small changes in exposure can have dramatic effects in this kind of light. One way to deal with this situation is to manually meter the part of the sky you want the birds silhouetted against, and add 1 stop to make it bright (you must however, monitor this continuously as the light changes rapidly at this time of day).
