What were these birds doing high overhead circling as a group?

Sometimes hawks and other birds of prey will catch the same wind currents and circle in them to gain altitude and relax a bit. I am not sure about the synchronized turns, but it may have just been a safety issue. If one bird turns the wrong way, it would prob. have been slammed into causeing an air collision. Another option could be that this group of birdshave interesting mating rituals. For example, penger pigeons flew in large groups and when their wings touched in the air it would stimulate the mating rituals/behaviors. I am not sure what other kinds of birds do this, but it could be possible.