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

Common Grackle Population Trend in Illinois

All statesGeneralists

Common Grackle in Illinois has fallen sharply: down 75% on the route-weighted index since 1968.

-75%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 →
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 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 75% 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 rise about 17% by 2029 — from 35 in 2024 to a central estimate of 41 (95% range 3.6–77). A 5-year backtest shows a typical error of ±56.1%, with 100% of held-out values landing inside the 95% band.

+17%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 →
41Projected 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 →
3.6–7795% 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 →
±56.1%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, Common Grackle in Illinois is projected to rise about 17% by 2029 — from 35 in 2024 to a central estimate of 41 (95% range 3.6–77). A 5-year backtest shows a typical error of ±56.1%, with 100% 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 →
2025471084
2026468.783
2027447.081
2028425.379
2029413.677

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
Fairbury15920241976
Pontiac14720241978
Gridley14420242001
Monticello13620241976
Cherry Val12420031972
Streator12220241972
Milford9220231966
Essex8020241969
Belleview7920241966
Buda7820231977
Troy Grove7820241993
Newark7620221969
Fairland7520241967
Mackinaw7220241966
Pawnee6720241967
Minonk6220241971
Rosamond6120241972
Caledonia5520241993
Beaucoup5420241971
Geneseo5220211967
Seneca5220241993
Mill Creek5120241966
Dailey5120221967
Marshall4920242001

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 2026-05-22.