Every fall, about 4 blocks from where I work, a natural phenom happens and tonight I went to witness it for the first time this season. For about 3 weeks in September, anywhere from 20,000-40,000 swifts nest in a chimney of an elementary school as they migrate south for the winter. What makes the nesting pretty spectacular is that at sunset the birds literally begin swarming in from all directions and start circling the chimney. They circle in one direction, all dive and start circling another direction, do more massive dives and fly-by's over the hundreds of spectators, then start circling the chimney again. Then just as the sun disappears they form a vortex and quickly the thousands and thousands of swifts head down into the chimney feet first where they latch onto the insides of the chimney and find rest for the night. This vortex of thousands of birds looks like a spinning tornado and the whole crowd cheers them on until the last swift is safely inside...pretty amazing!
I forgot my camera tonight so here are some pictures I found on flickr...enjoy!