BirdAnalyst
Species · Illinois · BBS 2026 Release · 1966–2025

Chimney Swift Population Trend in Illinois

All statesAerial insectivores

Chimney Swift in Illinois has fallen sharply: down 65% on the route-weighted index since 1968.

-65%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 →
59YearsYears 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 65% 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 35% by 2030 — from 5.2 in 2025 to a central estimate of 3.4 (95% range 0.00–8.6). A 5-year backtest shows a typical error of ±11.8%, with 100% of held-out values landing inside the 95% band.

-35%Change by 2030TrendPercent 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 →
3.4Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–8.695% 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 →
±11.8%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 35% by 2030 — from 5.2 in 2025 to a central estimate of 3.4 (95% range 0.00–8.6). A 5-year backtest shows a typical error of ±11.8%, with 100% of held-out values landing inside the 95% band.19662030
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 →
20264.40.009.6
20274.10.009.4
20283.90.009.1
20293.60.008.9
20303.40.008.6

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 →
Itasca7920251966
St Morgan2320221967
Compton1720251968
Delwood1720251970
Holcomb1620251971
Mascoutah Lk1520251967
Concord1220251967
Dudleyville1220252001
Barrington1120121967
Sterling1120232001
Harristown1120252001
Williamsfld1020251976
Bremen1020251969
Terre Haute920251966
Mackinaw920251966
Darmstadt920251993
Grape Creek920252001
Bradbury820251970
Birds820231976
Lake Summerset820252001
Buda720231977
Bartonville720251973
Beaucoup720251972
Seneca720251993
Concord West720252001

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 2026-08-14.