2011, Day 271 - Circling the drain

This is a regular occurrence during the month of September in northwest Portland.  The swifts stop off on their migration south and every year their favorite roost is the old disused chimney at Chapman Elementary School.  At their peak there may be more than ten thousand birds but as the cold weather becomes a fixture the numbers quickly dwindle down to hundreds and then to none as they move further south.  It is an amazing sight as the birds move in a synchronistic mass, moving as one large entity rather than the thousands of individuals that comprise the flock.  It is simply mesmerizing...

Canon 1D Mark IV, Canon 70-200/f2.8L IS Mark II
168mm, f3.2, 1/200 sec @ 1000 ISO