What Vaux’s swifts are and why they choose chimneys
Vaux’s swifts are small migratory birds that sleep in large flocks inside hollow trees and, in cities, brick chimneys. Portland sits on their route between western breeding grounds and winter homes in Central America and Venezuela.
A Vaux’s swift is a little over four inches long, with a cigar-shaped body, narrow crescent wings and a short, squared-off tail. It catches flying insects on the wing, and like other swifts it cannot perch on a branch or a wire. It clings to vertical surfaces instead, so the inside of a chimney serves it as well as a hollow snag.
Our chimney animal removal page covers the raccoons, squirrels and trapped birds that come out of a flue. Swifts are the one guest that stays put, so this guide is about the weeks you share the chimney with them and the chimney cap installation that sends the next flock somewhere else.
The Chapman Elementary roost, and why it moved
For about forty years the city’s famous roost was the chimney of a Northwest District school, Chapman Elementary: a brick stack built around 1925 that swifts filled each evening between mid-August and mid-October.
Estimates in different years ran from 1,700 to 35,000 birds. The school stopped running its heat during the roosting weeks, and donors later funded a separate heating system, which let the old stack stay with the birds year after year.
Then the counts fell. OPB reported a peak of more than 11,000 swifts on September 8, 2023, and more than 5,400 on September 2, 2024, and Hoodline reported the chimney empty by September 18 that year. Bird Alliance of Oregon found no blockage when its staff inspected the chimney that October.
In 2025 no swifts appeared at Chapman at all. The Southeast Examiner reported more than 7,000 at Abernethy Elementary and about 1,500 at St. Sharbel’s Catholic Church in Ladd’s Addition, and Hoodline reported that Bird Alliance biologists describe this kind of roost switching as normal for migrating swifts.
Recent fall roosts have shifted among school and church chimneys across Northwest, Northeast and Southeast Portland. When a big roost moves, any open masonry flue in the neighborhood can be a candidate, yours included.
A swift season in your chimney, week by week
The season runs from the middle of August to the middle of October, with Chapman’s largest recent counts in early September, and each stage asks something slightly different of you.
| When | What the swifts are doing | What you do |
|---|---|---|
| Mid-August | The first flocks reach the city and begin choosing chimneys at dusk | A cap fitted before birds settle in keeps them out; once they are using the flue, the cap waits |
| Late August | Numbers build toward the September peak | Damper closed, fireplace cold, nobody on the chimney top |
| Early September | Chapman’s recent peaks fell on September 2 and September 8 | Watch from the yard in the half hour after sunset to see which flue they use |
| Late September to early October | Numbers taper as the flocks head south | Keep the fire unlit, however raw the evening turns |
| Mid-October | The last birds leave for the winter | Count several empty evenings, then book the sweep and the cap |
At Chapman the swifts poured into the chimney over roughly thirty minutes after sunset and left at sunrise, so an evening watch tells you more than any daytime look. The Chapman roost also drew owls, peregrine falcons and Cooper’s hawks hunting the swifts, so a hawk on a nearby roof in September is part of the show.
Why nobody removes Vaux’s swifts from a chimney
Vaux’s swifts are on the federal list of birds protected by the Migratory Bird Treaty Act, which prohibits taking a protected species, killing and capturing included, without prior authorization.
Sweeping a flue full of roosting swifts, smoking them out or capping the top over them would harm or trap birds the law protects, so an occupied flue is left alone until the flock has gone.
So the plan is to wait, and waiting works. The roost lasts a few weeks, the flock heads for the tropics by itself, and an empty flue in late October is the moment for the sweep and the cap.
What to do while swifts are in your chimney
Leave the chimney alone and keep it cold; the steps below cover the details that come up in a Portland September.
- Keep the damper closed. The birds roost above it, and a closed damper keeps any that drop down out of the room. If the fireplace has glass doors, keep those shut as well.
- Keep every fire out of that flue. No kindling, no starter log and no burning paper to warm the flue, even when the first chilly evening arrives in late September.
- Leave the top of the chimney alone. No hose, no leaf blower, no cap, no screen and no crown work until the roost is empty.
- Mention any other flues when you call. If the same chimney also vents a furnace or water heater, say so, and make sure a carbon monoxide alarm works on that floor while the birds are in residence.
- Watch at dusk and write down the dates. The first evening you see them and the last one tell us when to schedule.
- Book once the evenings go quiet. A run of empty dusks in October is the sign the flock has moved on.
If what you hear is heavy scratching at night or a single bird fluttering at midday, it is probably not swifts. The page on scratching or chirping inside a chimney sorts out the other possibilities by sound, smell and time of day.
How to tell Vaux’s swifts from starlings
Swifts come in together at dusk late in the summer and never perch, while starlings are about twice their length, sit on wires and roof edges, and tend a nest through the day.
| Clue | Vaux’s swift | European starling |
|---|---|---|
| Size | About 4.2 to 4.4 inches long | About 7.5 to 9 inches long |
| Shape and look | Cigar-shaped body, long narrow crescent wings, short square tail | Stocky and short-tailed, glossy black with a purple or green sheen and white speckles at some times of year |
| Perching | Cannot perch on a wire or branch; clings to vertical surfaces | Perches on wires, gutters and roof ridges |
| When you see them | A flock pouring into the flue around dusk, gone at sunrise | Single birds or pairs flying in and out during daylight |
| Nest | A small cup of twigs glued to the flue wall with saliva | A bulky nest of straw, dry grass and twigs lined with feathers |
| Federal protection | On the Migratory Bird Treaty Act list | An introduced species, not on that list |
The last row does not change one rule we follow: a nest holding eggs or chicks is left alone until the young fly, no matter the species. Once a starling nest is empty, it comes out with the sweep and the cap goes on behind it.
When the cap can go on
A cap can go on any time the flue is empty of birds, which in practice means between late October and early August, with early summer the easiest stretch to book.
A stainless cap with spark arrestor mesh closes the flue to swifts without harming one, and it keeps out rain, raccoons and squirrels as well. The chimney cap types guide compares single-flue and multi-flue designs; on a stack with an unused flue, cover that flue too, since an idle passage is exactly what a roosting flock looks for.
Sweep before the cap goes on. The visit clears what weeks of roosting leave on the smoke shelf and damper, and the Level 1 check that is part of the visit confirms the flue is ready for the heating season. The maintenance calendar shows where the cap fits in the rest of the year.
If you want to keep a chimney for the swifts
A chimney with no appliance attached can be left open for swifts on purpose, as Chapman’s was, as long as you accept the rain that comes with an uncapped flue.
That choice suits a retired flue: a fireplace you no longer use, or the empty passage left beside a new high-efficiency furnace. Keep the damper closed, and have the chimney looked at every year, because an open top takes a full Portland winter of rain and the crown and mortar joints wear faster for it.
A flue you still use in the fall is the wrong one to share. The roost season overlaps the first fires of the year, and a fireplace that must stay cold until mid-October is one you will be tempted to light on a raw September night.