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Species · Illinois · BBS 2025 Release · 1966–2024

Worm-eating Warbler Population Trend in Illinois

All statesForest birds

Worm-eating Warbler in Illinois has risen sharply: up 63% on the route-weighted index since 1983.

+63%Since 1983TrendPercent 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 →
12Routes 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 →
38YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Worm-eating Warbler 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 Worm-eating Warbler in Illinois. See the full index history below.

Worm-eating Warbler Population Forecast in Illinois

If the recent trend holds, Worm-eating Warbler in Illinois is projected to stay roughly flat through 2029, near 0.05 (95% range 0.01–0.09). A 5-year backtest shows a typical error of ±64.1%, 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 →
0.05Projected 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 →
0.01–0.0995% 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 →
±64.1%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, Worm-eating Warbler in Illinois is projected to stay roughly flat through 2029, near 0.05 (95% range 0.01–0.09). A 5-year backtest shows a typical error of ±64.1%, with 100% of held-out values landing inside the 95% band.19782029
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 →
20250.050.010.09
20260.050.010.09
20270.050.010.09
20280.050.010.09
20290.050.010.09

Worm-eating Warbler Survey Routes in Illinois

Routes recording Worm-eating Warbler 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 →
Guilford119901989
Athens120222022
Payson120162016
Nilwood120142014
Sandusky120231993
Cave In Rock120232004
Marshall120162016
Eubanks120102007
Pulaski120172017
Bremen120231998
Delwood120241978
Karnak120162016

Worm-eating Warbler Population Trend in Other States

alabamaarkansasconnecticutdelawaregeorgiaindianaiowakentuckylouisianamarylandmassachusettsmississippimissourinew-hampshirenew-jerseynew-yorknorth-carolinaohiooklahomapennsylvaniarhode-islandsouth-carolinatennesseetexasvirginiawest-virginiawisconsin

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