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Species · Illinois · BBS 2025 Release · 1966–2024

Bell's Vireo Population Trend in Illinois

All statesForest birds

Bell's Vireo in Illinois has held roughly steady: up 9% on the route-weighted index since 1968.

+9%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 →
73Routes 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 Bell's Vireo 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 Bell's Vireo in Illinois. See the full index history below.

Bell's Vireo Population Forecast in Illinois

If the recent trend holds, Bell's Vireo in Illinois is projected to fall about 62% by 2029 — from 0.45 in 2024 to a central estimate of 0.17 (95% range 0.00–0.40). A 5-year backtest shows a typical error of ±68.4%, with 40% of held-out values landing inside the 95% band.

-62%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 →
0.17Projected 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 →
0.00–0.4095% 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 →
±68.4%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, Bell's Vireo in Illinois is projected to fall about 62% by 2029 — from 0.45 in 2024 to a central estimate of 0.17 (95% range 0.00–0.40). A 5-year backtest shows a typical error of ±68.4%, with 40% 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 →
20250.170.000.40
20260.170.000.40
20270.170.000.40
20280.170.000.40
20290.170.000.40

Bell's Vireo Survey Routes in Illinois

Routes recording Bell's Vireo 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 →
Chandlervill420241971
Kell420242001
Beaucoup320241974
Pulaski320242009
Brownville320241998
Geneseo219871967
Concord219961967
Belleview220231966
Humboldt220182005
Martinsville220181972
Robinson220221977
Royalton220242007
York220242004
Darmstadt220242014
Guilford120012001
Cherry Val119721972
Atkinson120242024
Payson120222009
Sheffield120111968
Buda120162016
Wayne119981998
Waynesville120072003
Dudleyville120222006
New Lenox119811981
Stillwell120111971

Bell's Vireo Population Trend in Other States

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