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

Tree Swallow Population Trend in Illinois

All statesAerial insectivores

Tree Swallow in Illinois has surged: up 163% on the route-weighted index since 1969.

+163%Since 1969TrendPercent 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 →
99Routes 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 Tree Swallow 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 increasecomputed 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 →

Tree Swallow has surged in Illinois: up 163% on the route-weighted index since 1969.

Tree Swallow Population Forecast in Illinois

If the recent trend holds, Tree Swallow in Illinois is projected to rise about 47% by 2030 — from 1.5 in 2025 to a central estimate of 2.2 (95% range 1.0–3.4). A 5-year backtest shows a typical error of ±49.4%, with 80% of held-out values landing inside the 95% band.

+47%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 →
2.2Projected 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 →
1.0–3.495% 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 →
±49.4%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, Tree Swallow in Illinois is projected to rise about 47% by 2030 — from 1.5 in 2025 to a central estimate of 2.2 (95% range 1.0–3.4). A 5-year backtest shows a typical error of ±49.4%, with 80% of held-out values landing inside the 95% band.19672030
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 →
20262.10.893.3
20272.10.923.3
20282.20.963.4
20292.20.993.4
20302.21.03.4

Tree Swallow Survey Routes in Illinois

Routes recording Tree Swallow 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 →
Seneca1320251998
Geneseo1220251970
Streator1020241974
Caledonia1020251994
Keithsburg1020252003
Gridley1020242009
Wayne920251974
Le Roy920251993
Holcomb720231973
Compton720251972
Janesville720252005
Lake Summerset720252001
Atkinson520241987
Gulfport520241984
Deer Creek520211992
Fairbury520252010
Yorkville520102009
Karnak520242002
Barrington420111970
Mackinaw420251967
Fairdale420242024
Cherry Val320011976
Bartonville320241973
Minonk320241991
Milford320251989

Tree Swallow Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.