I left the island to come down to Portland for a few days for a friend's wedding, and between the drive down and the social events surrounding the wedding this weekend I haven't had time to blog for a few days. This evening, however, my dad and I went out to dinner, and on the way we stopped at Force Lake in north Portland to see what sort of bird activity was going on. Several species were actively feeding including three great blue herons, a small flock of mallards, a belted kingfisher, some barn swallows, and a green heron - a great find! We also saw a pair of juvenile American coot:
There were also a lot of bullfrogs along the perimeter of the lake. These guys are unfortunately horribly invasive in this part of the country:
After dinner we went down to Chapman Elementary School where thousands Vaux's swifts (year bird 217) gather to roost in the school's chimney for the month prior to their southbound migration. Every night during September as many as 2000 people come out to see the swifts congregate and swirl through the air prior to sunset, then funnel into the chimney as darkness begins to fall.
Swifts are small (about four-inch long) insect-eating birds that never perch like you would picture a bird doing. They eat, drink, and even gather nesting materials and mate while on the wing. The only time they rest is while sleeping or nesting, and in these cases they cling to vertical surfaces using their claws and tails. They look a lot like swallows in flight, but have stiffer wings, so when flapping they always remind me of little airborne wind-up toys.
When we got there, there wasn't a swift to be seen. Suddenly, there were a few dozen. Then a few hundred. Then several thousand!
(For an interesting exercise in estimating bird numbers, how many swifts do you think are in the photo below? Go all the way to the bottom of this post for the answer.)
I saw this amazing spectacle a few years ago, and I think I went later in the month since there were more birds there than we saw tonight. Still, there were easily a couple thousand birds. The Portland Audubon Society has volunteers on site to educate the public about the birds, and they estimatesthat some years there are upwards 20,000 Vaux's swifts that roost in the chimney.
Until the year 2000, the students and teachers of Chapman Elementary would actually go without heat until the birds had left for their winter grounds. A fundraiser was held, however, to redo the heating system and decommission the chimney, leaving it as a permanent safe refuge for the swifts. Well, safe from human interference anyway...
That's a Cooper's hawk perched on the edge of the chimney. It's no surprise raptors have learned this a good place to catch a meal in the evenings. While the swifts are apparently too small for predators like red-tailed hawks, Cooper's hawks and peregrine falcons come to dine on them. This particular hawk caught one swift, flew to a nearby tree to eat it, then came back and caught a second one before all the swifts had descended into the refuge of the chimney tower. This "evil" hawk was met by boos from the onlookers, but hey, he's gotta make a living too!
The swifts are a beautiful sight to watch, but as they maneuvered through the air I found myself wondering what dictates their complicated choreography. The birds circle over the chimney for more than half an hour before sunset, diving down towards the opening but not going in. Other birds join in as they arrive at the roosting site from all directions. Occasionally the flock disperses, or veers away from the chimney before circling back. Then, about 5 or 10 minutes after sunset, they somehow all agree that it's time to enter the chimney and they funnel down to cling to the inside walls.
The photos don't quite do the whole thing justice, so here's a short video clip to give you more of an idea what this amazing spectacle is like!
(There are just under 200 birds in the first swift photo above. How close was your guess?)