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

Green Heron Population Trend in Illinois

All statesWetland birds

Green Heron in Illinois has declined: down 26% on the route-weighted index since 1968.

-26%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 →
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 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 stay roughly flat through 2030, near 0.22 (95% range 0.00–0.55). A 5-year backtest shows a typical error of ±31.1%, with 100% of held-out values landing inside the 95% band.

+5%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 →
0.22Projected 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 →
0.00–0.5595% 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 →
±31.1%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, Green Heron in Illinois is projected to stay roughly flat through 2030, near 0.22 (95% range 0.00–0.55). A 5-year backtest shows a typical error of ±31.1%, 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 →
20260.250.000.58
20270.250.000.57
20280.240.000.56
20290.230.000.55
20300.220.000.55

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
Mill Creek320121969
Mackinaw320211975
Mascoutah Lk320181979
Bremen320241969
York320241998
Cherry Val220021973
Putnam219961978
Newark220161969
Terre Haute220241971
Williamsfld220181980
Bradbury220231977
Humboldt220251991
Columbia220251966
Yale220021996
Gridley220142001
Marshall220252016
Royalton220132001
Guilford120191968
Holcomb120071978
Barrington119951972
Itasca120051983
Atkinson119911982
Geneseo120151967

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 2026-08-14.