These are psycho little birds that spend almost all day flying and only stop at night to sleep. They are not outfitted properly to perch, so they eat, drink, gather nest materials, and whatever else without stopping. They're crazy fast too. And at the school, there are thousands of them every evening for much of September and sometimes into October. The largest recorded flock was 35,000, although I have no idea how that compared to the night we were there.
In 1980-something, they just started showing up and using the school's chimney as a mass roost at night before flying to Central America at the first real cold snap. They fly around all day eating and then gather around sunset in the sky above the school. Shortly after sunset they start flying in a huge spiral getting tighter and tighter until one of them decides it's time to drop in, and then it looks like a giant whirlpool heading down into the chimney. For 20 or 25 years, they school just resigned itself to forgoing heat until the birds decided to leave. Then, a few years ago, they built a new natural gas furnace and left the old chimney as a permanent roost for the visitors.
Now, every evening for about three weeks in September, the Audubon Society has a regular event to watch the spectacle from a conveniently placed hillside. On the evening we went, there were maybe a couple hundred people and many brought dinner and cardboard for sliding down the hill. It was obvious that this was a regular event for many of them and I think we'll have to see it again too. Everybody even clapped and cheered after the last of the birds disappeared down the chimney. I'm not sure the birds cared, but we all had a good time. It reminded me a lot of people in Waikiki stopping at sunset to clap and cheer just as the last sliver of sun dips below the horizon.
We got the extra special version of the show the night we went. Right in the middle, a bird of prey flew right over the crowd and through the flock. It looked like a trick from an airshow, and the crowd reacted in much the same way. I assume it was a peregrine falcon, since they do live around here and hunt other birds. It seemed about the right size anyway. This must have looked like an all-you-can-eat buffet. Imagine birds flying everywhere overhead and making a huge chatter. Now imagine they all suddenly go silent at once and dart away from the chimney as this much larger, and much less maneuverable, bird barrels right through them. It didn't get anything that time, but a couple hundred (at least) of the most ill-tempered swifts followed it like a swarm of gnats. I'm not sure what they thought they were going to do to it. They could fly much faster than it could and darted back and forth trying to annoy it into leaving, I guess. All they managed to do was follow it as it made a large circle and came back quite a bit above the flock that was now back at the chimney. And this is where it showed them its trick. Although the peregrine falcon is not particularly fast in regular flight, it showed its fastest-bird-in-the-sky credentials by tucking in it's wings, leaving the gnat swarm in its dust, and dive bombing right back down through the middle of the flock scattering it again. A valiant effort, but still no luck. Those little guys are quick. Time for a change in tactics. It made a big circle again (with a new gnat swarm) and this time came in at treetop level and popped up into the birds that were much slower and fluttering right as they entered the chimney. The third time must have been the charm. It looked like it got something and it flew straight off without slowing or turning. A somewhat violent version of the show, but hey, a falcon's gotta eat too, right?