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Species · Illinois · BBS 2025 Release · 1966–2024

Northern Rough-winged Swallow Population Trend in Illinois

All statesAerial insectivores

Northern Rough-winged Swallow in Illinois has surged: up 458% on the route-weighted index since 1968.

+458%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 →
104Routes 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 Northern Rough-winged 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 →

Northern Rough-winged Swallow has surged in Illinois: up 458% on the route-weighted index since 1968.

Northern Rough-winged Swallow Population Forecast in Illinois

If the recent trend holds, Northern Rough-winged Swallow in Illinois is projected to rise about 28% by 2029 — from 2.5 in 2024 to a central estimate of 3.2 (95% range 1.7–4.8). A 5-year backtest shows a typical error of ±46%, with 80% of held-out values landing inside the 95% band.

+28%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 →
3.2Projected 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 →
1.7–4.895% 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 →
±46%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, Northern Rough-winged Swallow in Illinois is projected to rise about 28% by 2029 — from 2.5 in 2024 to a central estimate of 3.2 (95% range 1.7–4.8). A 5-year backtest shows a typical error of ±46%, with 80% 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 →
20253.11.54.6
20263.11.64.7
20273.21.64.7
20283.21.64.8
20293.21.74.8

Northern Rough-winged Swallow Survey Routes in Illinois

Routes recording Northern Rough-winged 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 →
Eldred24020211993
Melrose3519991975
Wayne3120241970
Stillwell3020241976
Gulfport2520241971
Sherrard2220241993
Pawnee2020181974
Camp Point1820241993
Guilford1320231974
Holcomb1120221972
Sheffield1120241967
Le Roy1120231994
Sandusky1120231993
Sterling1020232001
Fairdale920242019
Seneca720231993
Mill Creek520231967
Geneseo520001967
Compton520161973
Newark520191969
Minonk520241972
St Morgan520221983
Bremen520231972
New Lenox420191982
Terre Haute420241966

Northern Rough-winged 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.