Cause of Chimney Swift Death Unknown


On the morning of Wednesday, October 5, volunteers monitoring bird mortality in Center City found more than 20 dead chimney swifts to the east of Rittenhouse Square, according to Stephen Maciejewski, one of the volunteers. “I had found dead ones before, but never so perfectly preserved,” he said. “These were obviously fresh kills. They look so graceful.”

Another observer had noticed eight dead chimney swifts around French bistro Parc, Maciejewski reported. “I had finished my usual monitoring tour and went to the gym and was working out when I got the message. Within 20 minutes I was at 18th and Locust collecting birds.” The volunteers deposited the birds at the Academy of Natural Science of Drexel University for study. 

It is likely that many more died but were disposed of by building cleaning and maintenance staff on the sidewalks where they died. 

Chimney swifts spend summers in Philadelphia nesting and raising their young and in the fall migrate down to northern South America. They are highly adapted to a life in the air, with long wings and legs so small they cannot sit on flat surfaces. They can only cling to vertical surfaces, leading them to nest and roost (rest for the night) in vertical structures such as chimneys and grain silos. Migrating swifts travel during the day and at night roost in large numbers. In early fall, flocks of hundreds, and in some cases thousands, of swifts can be seen at dusk circling large chimneys in Philadelphia and then flying into them to spend the night. In recent years, large numbers of the chimney swifts have been seen roosting in the Barclay Hotel, at the southeast corner of Rittenhouse Square near where the dead swifts were found.

It is unclear how exactly these swifts died. Every year hundreds of millions of birds in North America die when they collide with windows, a hazard which led to a large mortality event in October 2020 and which inspired the Bird Safe Philly initiative. Many of the birds that die by colliding with windows migrate by night and touch down to feed during the day. Not having encountered glass before, they mistakenly fly towards reflections of trees and other vegetation and then get killed when they slam into the unexpectedly solid barrier. Chimney swifts, by contrast, migrate by day and hunt for flying insects as they go, which indicates that the Rittenhouse Square casualties likely died differently. 

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