The Vaux's Swift population in the U.S. and Canada has declined about 50 percent since 1970

A crowd of several hundred people gathered in the growing darkness outside Chapman Elementary School in Portland, Oregon, before the first Vaux's Swift darted into view high above. Minutes later, thousands of the tiny birds were swooping and swirling like a cloud of pulsating black ink as they circled a tall brick chimney silhouetted by the fading light. The humans below, watching from a patchwork of blankets and empty picnic baskets, cheered as the flock poured into the chimney all at once, like water spiraling down a drain.
The swifts' noisy migratory stopover each fall has made this chimney famous with bird lovers as far away as Europe and is a quirky Portland tradition so embraced by locals that the school keeps the diminutive Vaux's Swift as its mascot.The birds can fly for about 100 miles at a time between stops as they travel from Canada to Mexico and back each year and roost in large numbers in tight, enclosed spaces because their body temperature drops at night.

In recent years, fewer of the beloved birds have shown up. The official estimate of the Vaux's Swift (Chaetura vauxi) population in the U.S. and Canada is about 390,000, but there may be far fewer. The birds aren't listed as a threatened or endangered species, but their population has been falling 2 to 4 percent a year and has declined about 50 percent since 1970, said John Alexander, co-author of a regional conservation plan for Partners in Flight, a national alliance of bird-focused nonprofits and wildlife agencies.
Source: KVAL, September 30, 2016