128K views · 3.1K reactions | Thousands of chimney swifts are flocking to Hallahan High School, much to the delight of Philly birders. During their long migration south in the fall, chimney swifts will descend on a building by the thousands. They are especially attracted to chimneys they can funnel into at dusk. You can catch them at Hallahan most nights at dusk through early or mid-October.  by Frank Kummer / Staff | Philadelphia Inquirer | Facebook