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

Tree Swallow Population Trend in Illinois

All statesAerial insectivores

Tree Swallow in Illinois has surged: up 140% on the route-weighted index since 1969.

+140%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 →
57YearsYears 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 140% 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 stay roughly flat through 2029, near 2.2 (95% range 1.0–3.5). A 5-year backtest shows a typical error of ±45.1%, with 80% of held-out values landing inside the 95% band.

+8%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 →
2.2Projected 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 →
1.0–3.595% 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 →
±45.1%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, Tree Swallow in Illinois is projected to stay roughly flat through 2029, near 2.2 (95% range 1.0–3.5). A 5-year backtest shows a typical error of ±45.1%, with 80% of held-out values landing inside the 95% band.19672029
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 →
20252.10.893.3
20262.10.933.3
20272.20.963.4
20282.21.003.4
20292.21.03.5

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 →
Brnt Prairie1720241994
Geneseo1520181970
Janesville1420242005
Seneca1320241998
Fairbury1220242010
Streator1020241974
Gridley1020242009
Le Roy820241993
Holcomb720231973
Wayne720241974
Essex620241991
Humphrey620241982
Atkinson520241987
Gulfport520241984
Deer Creek520211992
Lake Summerset520222001
Yorkville520102009
Karnak520242002
Barrington420111970
Milford420231989
Belleview420241982
Fairdale420242024
Cherry Val320011976
Bartonville320241973
Minonk320241991

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 2026-05-22.