PANIC
Considering their low position in the food chain, it is not surprising that birds are quick to flee. What surprises me is how a flock of birds, even flocks numbering in the hundreds, can instantly communicate and simultaneously launch. Further, when in the air, how a huge flock can make a simultaneous right-angled turn without crashing into one another. I have watched flocks, with several hundred terns, launch into panicked flight, fly around the lagoon for several minutes, and then return to their original spot only to launch fifteen or twenty minutes later and do the same thing. The giant swarm can causes chaos for the other birds in the air, but they seem to manage without collisions.