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

Brown Thrasher Population Trend in Illinois

All statesGeneralists

Brown Thrasher in Illinois has fallen sharply: down 67% on the route-weighted index since 1968.

-67%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 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 67% 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 16% by 2029 — from 2.8 in 2024 to a central estimate of 2.4 (95% range 0.78–4.0). A 5-year backtest shows a typical error of ±5.3%, with 100% of held-out values landing inside the 95% band.

-16%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 →
0.78–4.095% 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 →
±5.3%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 16% by 2029 — from 2.8 in 2024 to a central estimate of 2.4 (95% range 0.78–4.0). A 5-year backtest shows a typical error of ±5.3%, 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 →
20252.71.14.3
20262.61.04.2
20272.60.964.2
20282.50.874.1
20292.40.784.0

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
Belleview1320241966
Athensville1020241971
Bremen1020241969
Payson1020242000
Mascoutah Lk820241967
Kell820242001
St Morgan720221967
Seneca720241993
Darmstadt720241993
Buda620231977
Chandlervill620241971
Melrose619991973
Birds620221976
Belknap620241970
Delwood620241970
Clayton620242001
Eubanks620242001
Marshall620242001
Terre Haute520241966
Cameron520241966
Beaverdam Lk520231970
York520241993
Newark420221969
Monticello420231976

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 2026-05-22.