PORTLAND, Ore. — It's a time-honored Portland tradition each September: grab a picnic basket and a few good friends and stake out a spot on the hill overlooking Chapman School in Northwest Portland, waiting for a spectacular show at sundown.
Thousands (usually) of tiny birds — Vaux's swifts — dance through the sky, swirling around the school's three-story-tall chimney, finally funneling inside to roost for the night. You'll hear shouts from the crowd as the birds are spotted, oohs and ahhs as they approach the chimney, loud boos for the birds of prey that eat a few of them, and applause throughout the crowd of thousands after the final little bird tucks into the chimney for bed.
It's a sight to behold, one you don't want to miss if you're in Portland in the fall, but if you're trying to hype up birdwatching to your new-to-town friends, a warning this year: you might be let down. That's because substantially fewer Vaux's swifts have returned to Chapman for their annual migration this year, and no one yet knows why.
"The numbers are quite a bit lower this year," said Joe Liebezeit, the assistant director of statewide conservation at the Bird Alliance of Oregon, formerly Portland Audubon. "In most years we get an average of 5,000 birds a night throughout September and in the peak in the middle of September, we'll often have a lot more than that."
Vaux’s swifts typically rely on hollow trees to serve as roosting sites, and they migrate through the Portland area each fall. With a decline in forest habitation, they also use chimneys throughout the area to roost.
The Bird Alliance counts the swifts that roost at Chapman every year. Their data from 2009 to 2022 shows a peak of 7,000 birds in mid-September. In 2023, the peak was 11,440 swifts at Chapman.
This year? The mid-September numbers have barely scratched 1,000.
"This year the numbers started out in the low thousands, and then trickled down into the hundreds," Liebezeit said. "In the past couple days, we haven't had any birds at Chapman."
The Bird Alliance's data shows that a high of 5,430 swifts were counted on September 2. Only 80 birds were counted on September 15.
Liebezeit said the Bird Alliance has been monitoring the Chapman chimney for 15 years, and he's never seen the count so low.
"It is very unusual," he said, but the birds have been known to find new homes. "These birds are known to sometimes forego using a chimney that they've used historically. We do know that there are some other chimneys in the Portland metro area that they're using in higher numbers than in previous years, so we're speculating right now that some of the birds that normally would be going into Chapman are going into chimneys in other parts of the town."
A video posted by Migration Brewing to social media earlier last week showed a swirling cloud of swifts over the chimney at Holy Trinity Greek Orthodox Cathedral, located a few blocks down from their Northeast Glisan location.
There also could be other things going on, Liebezeit said. The weather could play a factor, or there could be a higher number of hawks and falcons nearby, scaring the swifts away. Right now, it's too soon to definitely say what's keeping them away from Chapman.
"We really... we're just kind of scratching our heads."
The overall population of Vaux's swifts has declined over the past few decades, Liebezeit said, though not enough to call them an endangered species.
The Chapman chimney has hosted a flock of swifts since the 1980s. Back then, the kids went cold in the fall mornings to avoid turning on the furnace. In 2001, the school's heating system was converted to natural gas, but the chimney was preserved and seismically retrofitted to continue accommodating the swifts, which are also the school's mascot and a huge part of its identity. Kids wear Chapman Swifts clothing, the school is decorated with art projects involving the swifts, and events at the school are named after the birds.
Is the beloved tradition over? It's way too soon to say, Liebezeit said. Some years, the swifts leave a chimney, only to return in full the next year. He said they plan to look closely at their data from Chapman and other roosting sites around the city, as well as other experts along the birds' flyway to see what they're noticing.