Today Damon theorized an answer to my previous question — why big birds select V formation flying while little birds seem to prefer swarms.
The aerodynamic effects that bigger birds rely on to help reduce drag don’t help little birds that much, and more importantly thanks to the way little birds keep a roughly constant spacing in a swarm information from disturbances (like an incoming hawk swooping down) gets passed along as a wave like a traffic jam through the swarm, spreading the alert much more quickly than would be possible if each little bird had to look up and see the diving hawk. As a result the birds can react much more quickly and hopefully stay alive! Cool!
For more info, Damon suggests Princeton robotics, swarming & controls expert Prof. Naomi Leonard.