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

Great Blue Heron Population Trend in Illinois

All statesWetland birds

Great Blue Heron in Illinois has surged: up 257% on the route-weighted index since 1968.

+257%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 Great Blue 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 →

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 →

Great Blue Heron has surged in Illinois: up 257% on the route-weighted index since 1968.

Great Blue Heron Population Forecast in Illinois

If the recent trend holds, Great Blue Heron in Illinois is projected to rise about 119% by 2029 — from 1.1 in 2024 to a central estimate of 2.4 (95% range 1.1–3.7). A 5-year backtest shows a typical error of ±92.7%, with 40% of held-out values landing inside the 95% band.

+119%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 →
2.4Projected 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 →
1.1–3.795% 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 →
±92.7%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, Great Blue Heron in Illinois is projected to rise about 119% by 2029 — from 1.1 in 2024 to a central estimate of 2.4 (95% range 1.1–3.7). A 5-year backtest shows a typical error of ±92.7%, with 40% 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 →
20252.31.03.6
20262.31.13.6
20272.41.13.6
20282.41.13.7
20292.41.13.7

Great Blue Heron Survey Routes in Illinois

Routes recording Great Blue 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 →
Gulfport620231973
Fairbury620241990
Gridley620242001
Humboldt520221991
Columbia520231967
Beaucoup520241972
Flora520241985
Cherry Val 2520182004
Wayne420241972
Melrose419991973
Concord420231994
Janesville420241994
Mascoutah Lk420241989
Seneca420241994
Sheffield320241981
Deer Creek320241985
Minonk320241992
Athensville320231973
Belleview320241966
Rosamond320212000
St Morgan320221994
Bremen320231970
Shannon320181993
Camp Point320241993
Barrington220081979

Great Blue Heron 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.