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

Blue-gray Gnatcatcher Population Trend in Illinois

All statesForest birds

Blue-gray Gnatcatcher in Illinois has surged: up 18× on the route-weighted index since 1968.

18×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 →
97Routes 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 Blue-gray Gnatcatcher 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 →

Blue-gray Gnatcatcher has surged in Illinois: up 18× on the route-weighted index since 1968.

Blue-gray Gnatcatcher Population Forecast in Illinois

If the recent trend holds, Blue-gray Gnatcatcher in Illinois is projected to stay roughly flat through 2029, near 2.9 (95% range 2.2–3.6). A 5-year backtest shows a typical error of ±16%, with 80% of held-out values landing inside the 95% band.

+7%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 →
2.9Projected 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 →
2.2–3.695% 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 →
±16%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, Blue-gray Gnatcatcher in Illinois is projected to stay roughly flat through 2029, near 2.9 (95% range 2.2–3.6). A 5-year backtest shows a typical error of ±16%, with 80% 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 →
20252.72.03.4
20262.82.03.5
20272.82.13.5
20282.82.13.6
20292.92.23.6

Blue-gray Gnatcatcher Survey Routes in Illinois

Routes recording Blue-gray Gnatcatcher 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 →
Bremen2520241969
Royalton2020242001
Beaverdam Lk1920231970
Belleview1620241966
Cave In Rock1620241993
Pulaski1520241971
York1520241993
Robinson1220231997
Wayne1120232004
Mt Vernon920241973
Belknap920241973
Delwood920241973
Columbia820231970
Birds720241977
Sandusky720231993
Grape Creek720242002
Martinsville620241986
Beaucoup520241971
Marshall520242010
Terre Haute420241980
St Morgan420221969
New Lenox320172013
Dailey320171967
Eldred320191993
Brownville320241993

Blue-gray Gnatcatcher Population Trend in Other States

alabamaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourinebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawest-virginiawisconsinwyoming

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