I don't really know why, but it is always noticeable. Whenever the weather is going to change dramatically, the birds seem to act like they know what's ahead. And the one thing they always do is gather around each other. In particular, when we drive along I395 from DC to Virginia around the Jefferson Memorial, the pigeons - and other feathered friends - line up on the light posts. And every one of them is filled to the max. What's even more interesting is that they always seem to leave the same amount of space between each bird - perhaps so they don't bang in to each other when they take off in flight. It so happens this was the late morning when it was in the 70's, only to change to 40's by mid afternoon. I don't know if they remained all together when the winds kicked in, but they were most likely strategizing about what to do. It's hard to fool Mother Nature. I'm sure they were all prepared to deal with it.