a flock of friends or foes?

On my way to Bible study last night, my attention was caught by a large gathering of little black birds at the corner of Marsh and Preston. It must be a yearly occurrence because I remember seeing them last fall, too. Around dusk, they begin to gather by the hundreds, filling the tops of every tree lining the street, as well as all of the telephone wires. It is almost a creepy sensation to drive through the intersection as their chirping and cheeping and cawing fills your ears, but last night I was merely curious. What makes them gather every year only in the fall and only at dusk? Why these trees at this intersection? Who organized this meeting? Is there a city bird council to debate important matters concerning safe aviation and the successful marking of cars? Maybe it's a secret meeting to discuss an overthrow or uprising against the current goverment...Or maybe they're interested in helping us humans keep our city clean and they're going to organize a trash pick-up day.

Whatever it is, I really would like to know...