Walking home today through one of my favorite 1930's neo-Tudor neighborhoods (and feeling just a bit sorry for myself that soon I'll be back in my own 1950's subdivision, where there's not a single diamond-paned window to be found), I was drawn out of my funk by the sound: the twittering of quite a large number of birds, species unknown. No birds were visible in the immediate area, so I knew that the sound had to be coming from a large flock of something.
Finally; a few hundred feet away, I saw them: dozens of starlings in the upper branches of two enormous, spreading trees, probably oak or maple of some kind, their cheerful chatter drowning out the traffic from a busy street only a block away. It quickly became obvious why a group of starlings is called a murmuration, which dictionary.com defines as "a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech." Starlings have no lips, but the sounds they were making were continuous, and as much as I would have liked to know what they were saying to each other, their speech was not articulate from a human perspective. But it was a delight to see and hear so many birds congregating and murmurating on a grey November noon.
"Murmuration" also describes a specific kind of flocking behavior: the tendency of starlings to swoop in huge groups shortly before roosting in the evenings. If you want to see a real murmuration and have a shortage of starlings roosting in your neighborhood, you can watch a video of an enormous Irish flock here.
Closer to home, near the drainage ditch that has become a protected stream, I could hear the twitters of large numbers of much smaller birds. Not even meandering along the margin gave a good look at the flock, which was hiding in thick vegetation that included way too much tatarian honeysuckle. Based on the two individuals brave enough to venture into the stream, I suspect that I was hearing a spattering of sparrows.