I’ve been meaning to put this online for a while.
I spent a few days in Rome this spring, where each evening just after five o’clock, tens of thousands of birds assembled massive swarms over the train station Roma Termini. The first time I saw them, I stood there for almost an hour. The constant collective motion of the incredible mass of individual animals was more akin to liquid and smoke than the movement of single agents.
I tried to take a couple of videos with my old digital camera. They really don’t do the phenomenon justice, but if you’re interested in flocking behaviour or have tinkered with boids, I’m sure you’ll like these.

Both videos are Quicktime, around 2.5 MB in size.
video 1
video 2