Vaux’s swifts return early to Portland this year, but climate change might not be the only reason...

The tiny Vaux’s swifts, birds that put on a magnificent aerial display in Portland every September, arrived early this year.

They’re already numbering in the thousands, when they’d usually only be in the hundreds. And that’s prompting concerns about the impact of climate change.

The swifts arrive in the Pacific Northwest every spring to breed. They’re dark, narrow-winged birds that usually use a hollow tree in which to make a nest.

But each fall in Portland, some preparing for their annual migration to Central America use the big chimney at Chapman Elementary School in Northwest Portland as a drier, warmer option.

“When you have a large flock of birds there’s a stronger ability for them to be vigilant and look out for predators,” said Joe Liebezeit, an assistant director of statewide conservation with Portland Audubon.