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Swifts, the fast birds with the shape of cigars, have had an up/down relationship with humans here and throughout the country.

Before settlement our swifts — chimney swifts — nested in small numbers in hollow trees and on cave walls. We arrived, and swift populations grew because every home, every heated building had an old-fashioned rough brick chimney. And then they didn’t.

Boom to bust.

Chimney swift populations are in decline. Hollow trees are gone; we like neat yards and parks. Brick chimneys are mostly past tense, fireplaces the remaining source.

Plus, all swift species live on flying insects captured on the wing. Insects are going the way of chimneys.

In our 15 years in this house I’ve been able to count on swift sightings each summer. They flew from a neighborhood to our north with big homes, fireplace homes. Last year, I spotted no swifts.

Happenstance? Things do change. Chimneys get capped. Birds die sooner or later. Maybe there just weren’t enough airborne bugs. (Although a friend a mile away has swifts in her neighborhood, even nesting in her fireplace chimney!)

You watch for swifts high up, cutting long arcs over yards and homes or above commercial buildings, those perhaps attracted by the insects drawn to parking-lot light.

Up close look

I had a unique opportunity a few years ago. An acquaintance had a home with a fireplace chimney in which swifts nested. He and his wife went on an extended vacation. His caretaker, a friend of mine, helped with the ladder that gave me access to the flat roof.

I was up there twice, once peering down the chimney to see a nest with eggs, the second time finding swifts clinging to chimney walls. I have the photos to prove it. (That won’t happen again; sorry to say the house was torn down.)

I’ve also watched fall pre-migration flocks as hundreds of swifts gather to roost in suitable chimneys. The birds arrive at dusk, swirl above the chimney, and funnel in.

Old brick buildings with old large chimneys are best if you want to watch. Schools can be good places to check.

Species in need

Chimney swift numbers have declined by about 50% over the past 40 years, with the most precipitous drop in the past decade, according to Audubon Minnesota.

The International Union for the Conservation of Nature and Natural Resources, the world’s main authority on the conservation status of species, recently elevated the threat category for these swifts to “Near Threatened,” Audubon Minnesota reports.

There are three other North American swift species, all western birds: black swift, white-throated swift and Vaux’s swift.

Two nest on ledges or crevices in steep cliffs. Vaux’s relies on hollow trees, contending with practices that reduce old-growth forests.

All three species have populations in decline, labeled by Audubon as of “great concern.”

Chimney swifts build nests of twigs and spit. They break off twigs in flight, securing them to chimney walls with saliva that thickens in nesting season. On an old nest the saliva resembles dried egg white.

People build wooden nesting towers for swifts to use. You can find plans at chimneyswifts.org

Chimney swifts live at the edges of our awareness. We don’t often scan the sky. We almost never hear swifts unless you detect their chittering in your chimney.

We have unwittingly made them dependent on us. They are marvelous little birds. Check your piece of sky. We should pay attention while we can.

Lifelong birder Jim Williams can be reached at woodduck38@gmail.com. Join his conversation about birds at startribune.com/wingnut.