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

Common Grackle Population Trend in Illinois

All statesGeneralists

Common Grackle in Illinois has fallen sharply: down 74% on the route-weighted index since 1968.

-74%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 Common Grackle 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 →

Common Grackle has fallen sharply in Illinois: down 74% on the route-weighted index since 1968.

Common Grackle Population Forecast in Illinois

If the recent trend holds, Common Grackle in Illinois is projected to stay roughly flat through 2030, near 38 (95% range 1.1–75). A 5-year backtest shows a typical error of ±54.8%, with 100% of held-out values landing inside the 95% band.

+10%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 →
38Projected 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 →
1.1–7595% 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 →
±54.8%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, Common Grackle in Illinois is projected to stay roughly flat through 2030, near 38 (95% range 1.1–75). A 5-year backtest shows a typical error of ±54.8%, 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 →
2026458.081
2027436.280
2028414.578
2029402.876
2030381.175

Common Grackle Survey Routes in Illinois

Routes recording Common Grackle 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 →
Atkinson25020241966
Gridley16820252001
Streator13320251972
Fairbury13320251976
Beaucoup12920251971
Cherry Val12420031972
Fairland11920251967
Monticello11520251976
Essex10320251969
Le Roy9820251993
Gulfport7920251971
Buda7820231977
Newark7620221969
Seneca7420251993
Marshall7420252001
Troy Grove7320251993
Pontiac7120251978
Rosamond6820251972
Minonk6220241971
Mackinaw6020251966
Pawnee4920251967
Greenview4820251993
Grape Creek4720252001
Caledonia4520251993
Itasca4420251966

Common Grackle Population Trend in Other States

alabamaarkansascoloradoconnecticutdelawarefloridageorgiaidahoindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawest-virginiawisconsinwyoming

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