‘A living cloud’: Hallahan High School becomes a birder attraction as chimney swifts fly in by the thousands

The first tiny dots in the sky appeared above the vacant John W. Hallahan Catholic Girls’ High School at 7:10 p.m.

They swooped closer, grouping by the hundreds: chimney swifts arriving for their nightly show above the school, drawing oohs and aahs from 55 people who had gathered to see the spectacle.

The birds formed a cloud, funneling like a bird tornado above Hallahan’s big open brick chimney, before diving inside for the night. Then came another cloud. And another, followed by more. It was over by 7:20 p.m., and the crowd that assembled along Wood Street broke into applause for the 10-minute show.

“It was fantastic,” said Ryan Sullivan, a city resident.

Sullivan is not an ardent birder but saw a listing for a “Swift Watch” on the city’s Parks and Recreation calendar and assumed it was not about Taylor. Curious, he clicked the listing and saw a description about gathering to watch the birds migrate and “roost together.” It sounded interesting, so he and Ann Watts found child care and arranged a date night out to attend.

“It lived up to expectations,” Watts said.

Thursday evening’s Swift Watch was organized by Rob Karchnyak of the Delaware Valley Ornithological Club (DVOC). The club also hosted a watch event Sept. 12. Hallahan is not the only open chimney where the birds flock. But Hallahan, at North 19th and Wood Streets in Franklintown, has become a convenient go-to spot.

Karchnyak estimated 2,700 chimney swifts came Sept. 12, though he admits counting is tough.

“I count them in groups of hundreds. I try to be conservative, too, so that I wouldn’t over count. But I’m likely under counting.”

The viewing spot became popular after DVOC member Judy Stepenaskie, who has been monitoring a few chimney swift gathering sites in the city for years, began watching Hallahan’s chimney a few years ago. The school closed in 2021.

She said the birds especially like the city’s older schools with wide-open chimneys. She has monitored other Philadelphia locations, such as the Shawmont School in Northwest and the Mifflin School in East Falls.

“I’ve known about Hallahan for years,” Stepenaskie said. “But it’s only recently that we’ve had these real big numbers. Last year at the end of September, we had over 10,000 chimney swifts for a couple of nights in a row.”

During their long migration south in the fall, chimney swifts (Chaetura pelagica) will descend on a building by the thousands, especially attracted to chimneys they can funnel into at dusk. The birds spend most of their life flying, touching down only to roost for the night, feasting on thousands of mosquitos as they cruise.

They don’t normally perch but prefer to cling to the walls of chimneys and other vertical surfaces with their long claws and a glue-like saliva from under their tongues, according to Cornell University. Unused chimneys also provide warmth on cold nights.

The birds eventually fly south to winter in the upper Amazon basin of Peru, Ecuador, Chile, and Brazil.

Stephen Maciejewski, a Philadelphia resident and another DVOC member, said Philly has become a chimney swift capital because it still has a number of old chimneys. He attended both chimney swift watch events. The birds come at dusk, which changes as days shorten in the fall.

“The way they twist and turn, their choreography is really amazing,” Maciejewski said. “They’re like a living cloud and form into a funnel shape. It’s amazing. I don’t know how they maneuver into a small opening in the chimney and not collide with one another. It’s a wonder of nature.”

The dark gray-brown, cigar-shaped birds emit fast, high-pitched notes that last only a few seconds but become a raucous buzz when they are together. They are small birds about five inches long and weigh about an ounce, roughly between the size of a sparrow and a robin.

“A lot of chimneys are capped so that birds can’t use them,” Maciejewski said.

The chimney swifts start descending on Hallahan most nights at dusk starting in September through early or mid-October. They gravitate toward the big brick chimney, which provides a rough, easy-to-cling surface.

Peak chimney swift activity seems to be the end of September.

Chimney swifts have long been in decline, with numbers dipping about 67% since the 1960s, according to the North American Breeding Bird Survey. The birds, which originally roosted in hollow trees, likely became numerous as colonists cleared forests and traditional brick chimneys became common. More modern chimneys are not as suitable, and owners cap them. And many old buildings simply get razed.

But it’s unclear how many more years Hallahan will remain a vacant sanctuary for the birds. The building, which is just off Vine Street, is being eyed by Belmont Charter Network to house its high school. The campus includes a gym, auditorium, and cafeteria. Belmont Futures purchased the property for $7.5 million in April, according to city tax records.

The DVOC has sent a letter to the new owners to see whether there’s a way to keep the chimney accessible to the birds but have not yet heard back.

At the end of the breeding season, the birds begin their fall migration, congregating in flocks at suitable roost sites. The website chimneyswifts.org has information on the birds and how chimneys can be made to accommodate them.

The DVOC is trying to gather more information about where chimney swifts roost in Philadelphia, and are asking anyone with information to send an email to conservation@dvoc.org and provide the location.