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

Green Heron Population Trend in Illinois

All statesWetland birds

Green Heron in Illinois has declined: down 27% on the route-weighted index since 1968.

-27%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 →
101Routes 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 Green Heron 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 →

No notable trend signals for Green Heron in Illinois. See the full index history below.

Green Heron Population Forecast in Illinois

If the recent trend holds, Green Heron in Illinois is projected to fall about 12% by 2029 — from 0.27 in 2024 to a central estimate of 0.23 (95% range 0.00–0.56). A 5-year backtest shows a typical error of ±46.7%, with 100% of held-out values landing inside the 95% band.

-12%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 →
0.23Projected 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 →
0.00–0.5695% 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 →
±46.7%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, Green Heron in Illinois is projected to fall about 12% by 2029 — from 0.27 in 2024 to a central estimate of 0.23 (95% range 0.00–0.56). A 5-year backtest shows a typical error of ±46.7%, 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 →
20250.270.000.59
20260.260.000.58
20270.250.000.58
20280.240.000.57
20290.230.000.56

Green Heron Survey Routes in Illinois

Routes recording Green Heron 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 →
Dailey520051972
Belleview420231967
Belknap420241970
Mill Creek320121969
Mackinaw320211975
Mascoutah Lk320181979
Bremen320241969
York320241998
Cherry Val220021973
Putnam219961978
Wayne220231969
Newark220161969
Terre Haute220241971
Williamsfld220181980
Bradbury220231977
Pulaski220221970
Camp Point220151996
Yale220021996
Gridley220142001
Royalton220132001
Guilford120191968
Holcomb120071978
Barrington119951972
Itasca120051983
Atkinson119911982

Green Heron Population Trend in Other States

alabamaarizonaarkansascaliforniaconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourinebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawashingtonwest-virginiawisconsin

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.