Each fall huge numbers of Vaux’s Swifts pass down the West Coast of the United States during their southern migration. At night they will gather for the night in massive communal roosts. Before the advent of man and his structures, they would gather in huge numbers inside of hollowed out tree trunks (redwood trees that had been cored by fire, oaks hollowed out by rot, etc.) Now however they love a good unused chimney, especially ones of a more industrial size- old brick factory kilns, disused boilers for campuses, etc. One such chimney is in Healdsburg, California, at a private school.
Luckily for the birding community and the curious, this school is kind enough to open up its campus each night to allow people to view the phenomenon of several thousand swifts descending into the school’s old boiler chimney. Up to 20,000 swifts can funnel into the chimney in the space of 2-10 minutes. On the night I took this video (Monday September 19, 2011) at least 3,500 swifts descended into this manmade roost, and perhaps as many as 8,000- I am horrible at estimating the number of swifts.
Enjoy the video (which since my main cameras are all at the doctors was shot with my iPhone).