BirdAnalyst
Species · Illinois · BBS 2025 Release · 1966–2024

Chimney Swift Population Trend in Illinois

All statesAerial insectivores

Chimney Swift in Illinois has fallen sharply: down 66% on the route-weighted index since 1968.

-66%Since 1968TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
105Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
58YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Chimney Swift Trends in IllinoisNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

long arc declinecomputed indexTrend sourceWhether the figure is our own computed route-weighted index or an official USGS modeled estimate. The current build labels every trend as computed.Full methodology →

Chimney Swift has fallen sharply in Illinois: down 66% on the route-weighted index since 1968.

Chimney Swift Population Forecast in Illinois

If the recent trend holds, Chimney Swift in Illinois is projected to fall about 15% by 2029 — from 4.2 in 2024 to a central estimate of 3.6 (95% range 0.00–8.9). A 5-year backtest shows a typical error of ±10.1%, with 100% of held-out values landing inside the 95% band.

-15%Change by 2029TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
3.6Projected 2029 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–8.995% range95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
±10.1%Backtest errorBacktest errorTypical error when we hold out the most recent years, forecast them, and compare to what actually happened. Lower means a more trustworthy projection.Full methodology →
If the recent trend holds, Chimney Swift in Illinois is projected to fall about 15% by 2029 — from 4.2 in 2024 to a central estimate of 3.6 (95% range 0.00–8.9). A 5-year backtest shows a typical error of ±10.1%, with 100% of held-out values landing inside the 95% band.19662029
Projection of the recent trend (dashed) with 80/95% bands — a projection, not a prediction. Habitat, climate, and land use are not modeled.
YearProjected indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →95% low95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →95% high95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
20254.60.009.9
20264.30.009.6
20274.10.009.4
20283.80.009.1
20293.60.008.9

Chimney Swift Survey Routes in Illinois

Routes recording Chimney Swift in Illinois.
Recent countThe raw number of individuals recorded on this route in its most recent survey year. A single-route tally, not a trend.Full methodology →
Itasca6420241966
Beaucoup3120241972
St Morgan2320221967
Dudleyville2220242001
Concord1320241967
Barrington1120121967
Belleview1120241966
Sterling1120232001
Columbia1020231966
Mascoutah Lk1020241967
Williamsfld920241976
Alden920232019
Birds820231976
Grape Creek820242001
Holcomb720241971
Buda720231977
Essex720241970
Cameron720241966
Caledonia720241993
Cherry Val620031973
Bartonville620241973
Humboldt620221970
Mt Vernon620221972
Pulaski620241970
Bremen620241969

Chimney Swift Population Trend in Other States

alabamaarkansascoloradoconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.