I spent a few hours watching a flock of red-winged blackbirds fly from tree to tree the other day and noticed something interesting. While the birds were all sitting in a tree (and there were several hundred of them) they were quite loud and chattered nonstop. Then suddenly the entire group would go silent in unison and about 1 or 2 seconds later would all fly on to the next tree, maintaining their silence. I've read a bit about flock dynamics and how they work by obeying local rules, each bird watching the other birds around them. But how does the entire flock know exactly when to go silent, and do so in such perfect synchronicity? Is this even a question we know the answer to? I would understand if it took the birds a few seconds to all quiet down and then depart in scattered groups headed toward the next tree. But every single bird was perfectly silent in under a second.

Sorry that nobody seems to have a good answer to this.

My hypothesis, and it is just that, would be that "silence" spreads through the group based on similar heuristics to those that could explain flock dynamics (e.g. if your neighbours have stopped chattering then you should be quiet).