A flock of approximately fifty pigeons hang out on the ledge of the fourth story of the building across the parking lot from my office. They have a leader who rests separate from all the others, right on the end of this ledge. When he takes flight, so do the rest. They fly in formation, making three elliptical laps in the sky directly above the parking lot. The pigeons do this several times a day.
In my mind, this is their way of exercising. There seems to be no other reason why these pigeons would do this, except maybe to find food, but a pigeon almost never breaks formation. When there is a straggler, he finishes his three laps and joins the rest back on the ledge, and that is the most unique part of this observation.