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Species · Illinois · BBS 2026 Release · 1966–2025

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 →
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 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 2030, near 2.9 (95% range 2.2–3.7). A 5-year backtest shows a typical error of ±15.8%, with 80% of held-out values landing inside the 95% band.

+8%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 →
2.9Projected 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 →
2.2–3.795% 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 →
±15.8%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 2030, near 2.9 (95% range 2.2–3.7). A 5-year backtest shows a typical error of ±15.8%, with 80% 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 →
20262.82.03.5
20272.82.13.5
20282.82.13.6
20292.92.23.6
20302.92.23.7

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 →
Bremen3020251969
Pulaski2420251971
Belleview2220251966
Beaverdam Lk1920231970
Royalton1720252001
Cave In Rock1620241993
Mt Vernon1220251973
Robinson1220231997
Bradbury1020251972
Delwood820251973
Birds720241977
Sandusky720231993
Yale620251993
Athensville520251972
Belknap520251973
York520251993
Terre Haute420251980
Martinsville420251986
St Morgan420221969
Marshall420252010
Athens420252009
Wayne320252004
New Lenox320172013
Dailey320171967
Union320172013

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 2026-08-14.