BirdAnalyst
Species · Illinois · BBS 2026 Release · 1966–2025

Prothonotary Warbler Population Trend in Illinois

All statesForest birds

Prothonotary Warbler in Illinois has surged: up 222% on the route-weighted index since 1968.

+222%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 →
36Routes 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 Prothonotary 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 →

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 →

Prothonotary Warbler has surged in Illinois: up 222% on the route-weighted index since 1968.

Prothonotary Warbler Population Forecast in Illinois

If the recent trend holds, Prothonotary Warbler in Illinois is projected to fall about 19% by 2030 — from 0.35 in 2025 to a central estimate of 0.28 (95% range 0.13–0.44). A 5-year backtest shows a typical error of ±48.1%, with 0% of held-out values landing inside the 95% band.

-19%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 →
0.28Projected 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 →
0.13–0.4495% 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 →
±48.1%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, Prothonotary Warbler in Illinois is projected to fall about 19% by 2030 — from 0.35 in 2025 to a central estimate of 0.28 (95% range 0.13–0.44). A 5-year backtest shows a typical error of ±48.1%, with 0% 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 →
20260.270.110.42
20270.270.120.43
20280.270.120.43
20290.280.120.43
20300.280.130.44

Prothonotary Warbler Survey Routes in Illinois

Routes recording Prothonotary 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 →
Beaverdam Lk720231970
Belleview620251966
Pulaski620251970
Birds320241978
Karnak320232003
Eldred319951995
Newark220142014
Mascoutah Lk220231981
Beaucoup220251994
Brnt Prairie220251987
Belknap220251973
Royalton220252003
York220251994
Athens120152015
Geneseo120251971
Gulfport120232023
Chandlervill119731973
Athensville120031979
Concord120041983
Pawnee120021979
Fairland119941994
Lake Summerset120252012
Humboldt120232023
Columbia119681968
Jamestown120251971

Prothonotary Warbler Population Trend in Other States

alabamaarkansasdelawarefloridageorgiaindianaiowakansaskentuckylouisianamarylandmichiganminnesotamississippimissourinew-jerseynew-yorknorth-carolinaohiooklahomapennsylvaniasouth-carolinatennesseetexasvirginiawest-virginiawisconsin

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