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

Great Horned Owl Population Trend in Illinois

All statesGeneralists

Great Horned Owl in Illinois has declined: down 27% on the route-weighted index since 1970.

-27%Since 1970TrendPercent 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 →
89Routes 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 →
56YearsYears 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 Horned Owl 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 Great Horned Owl in Illinois. See the full index history below.

Great Horned Owl Population Forecast in Illinois

If the recent trend holds, Great Horned Owl in Illinois is projected to stay roughly flat through 2029, near 0.11 (95% range 0.00–0.30). A 5-year backtest shows a typical error of ±357.3%, with 100% of held-out values landing inside the 95% band.

n/aChange 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 →
0.11Projected 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 →
0.00–0.3095% 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 →
±357.3%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 Horned Owl in Illinois is projected to stay roughly flat through 2029, near 0.11 (95% range 0.00–0.30). A 5-year backtest shows a typical error of ±357.3%, 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 →
20250.120.000.31
20260.110.000.31
20270.110.000.30
20280.110.000.30
20290.110.000.30

Great Horned Owl Survey Routes in Illinois

Routes recording Great Horned Owl 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 →
Humboldt520191977
Mill Creek320231971
Cherry Val219951977
Compton220061984
Streator219851981
Newark220211995
Williamsfld219921979
Milford220011992
Clarksdale220141988
Janesville219811981
Jamestown219961996
Mt Vernon219981992
Bremen220121970
Beaverdam Lk219941985
Lake Summerset220112002
Waynesville220122002
Royalton220232023
Guilford119881984
Holcomb119851985
Barrington120051995
Geneseo120151973
Putnam119991974
Sheffield120141966
Buda120231985
Wayne120031988

Great Horned Owl 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.