This is evidently not an uncommon occurrence. Apart from signaling the onset of the End Times, small birds also do this for safety:
When frightened by a flying predator, a flock of small birds such as sandpipers or starlings will bunch up and fly in as compact a mass as possible. A dive-bombing falcon will avoid plunging into such a crowd for fear of injuring itself in a collision, but instead will seek to pick off laggards or birds shearing away from the flock. The flock itself will veer and turn in erratic fashion, making it difficult for the predator to predict its movements. [The Straight Dope]
