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Species · Illinois · BBS 2026 Release · 1966–2025

Vesper Sparrow Population Trend in Illinois

All statesGrassland birds

Vesper Sparrow in Illinois has declined: down 43% on the route-weighted index since 1968.

-43%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 →
86Routes 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 Vesper Sparrow 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 Vesper Sparrow in Illinois. See the full index history below.

Vesper Sparrow Population Forecast in Illinois

If the recent trend holds, Vesper Sparrow in Illinois is projected to rise about 31% by 2030 — from 3.4 in 2025 to a central estimate of 4.4 (95% range 2.5–6.4). A 5-year backtest shows a typical error of ±65.3%, with 40% of held-out values landing inside the 95% band.

+31%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 →
4.4Projected 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 →
2.5–6.495% 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 →
±65.3%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, Vesper Sparrow in Illinois is projected to rise about 31% by 2030 — from 3.4 in 2025 to a central estimate of 4.4 (95% range 2.5–6.4). A 5-year backtest shows a typical error of ±65.3%, with 40% 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 →
20264.42.56.4
20274.42.56.4
20284.42.56.4
20294.42.56.4
20304.42.56.4

Vesper Sparrow Survey Routes in Illinois

Routes recording Vesper Sparrow 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 →
Buda2420231977
Pontiac2120251978
Fairland2120251967
Fairbury1620251976
Atkinson1520241966
Le Roy1520251993
Streator1320251972
Monticello1320251976
Shannon1320251993
Grape Creek1320252001
Essex1220251969
Sheffield1120241966
Minonk1120241976
Birds1120101982
Harristown1120252006
Holcomb1020251972
Troy Grove1020251993
Gridley1020252001
Williamsfld920251973
Seneca920251993
Sterling920232001
Newark820221969
Mackinaw720251966
Milford620251966
Caledonia620251993

Vesper Sparrow Population Trend in Other States

arizonacaliforniacoloradoconnecticutdelawareidahoindianaiowakansaskentuckymainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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