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Species · Illinois · BBS 2026 Release · 1966–2025

Brown Thrasher Population Trend in Illinois

All statesForest birds

Brown Thrasher in Illinois has fallen sharply: down 66% on the route-weighted index since 1968.

-66%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 →
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 Brown Thrasher 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 declinecomputed 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 →

Brown Thrasher has fallen sharply in Illinois: down 66% on the route-weighted index since 1968.

Brown Thrasher Population Forecast in Illinois

If the recent trend holds, Brown Thrasher in Illinois is projected to fall about 24% by 2030 — from 3.1 in 2025 to a central estimate of 2.3 (95% range 0.74–3.9). A 5-year backtest shows a typical error of ±6.3%, with 100% of held-out values landing inside the 95% band.

-24%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 →
2.3Projected 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 →
0.74–3.995% 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 →
±6.3%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, Brown Thrasher in Illinois is projected to fall about 24% by 2030 — from 3.1 in 2025 to a central estimate of 2.3 (95% range 0.74–3.9). A 5-year backtest shows a typical error of ±6.3%, 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 →
20262.71.14.3
20272.60.994.2
20282.50.914.1
20292.40.824.0
20302.30.743.9

Brown Thrasher Survey Routes in Illinois

Routes recording Brown Thrasher 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 →
Flora1420221976
Belleview920251966
Mascoutah Lk920251967
Delwood920251970
Kell820252001
St Morgan720221967
Mt Vernon720251971
Camp Point720251993
Buda620231977
Stillwell620251971
Melrose619991973
Athensville620251971
Birds620221976
Duncan Mills620251993
Clayton620252001
Karnak620252001
Streator520251972
Concord520251967
Humphrey520251972
Belknap520251970
Beaverdam Lk520231970
Sherrard520251993
York520251993
Darmstadt520251993
Dudleyville520252001

Brown Thrasher Population Trend in Other States

alabamaarkansascoloradoconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.