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

Vesper Sparrow Population Trend in Illinois

All statesGrassland birds

Vesper Sparrow in Illinois has declined: down 44% on the route-weighted index since 1968.

-44%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 →
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 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 65% by 2029 — from 2.7 in 2024 to a central estimate of 4.5 (95% range 2.6–6.4). A 5-year backtest shows a typical error of ±58.3%, with 40% of held-out values landing inside the 95% band.

+65%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 →
4.5Projected 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 →
2.6–6.495% 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 →
±58.3%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 65% by 2029 — from 2.7 in 2024 to a central estimate of 4.5 (95% range 2.6–6.4). A 5-year backtest shows a typical error of ±58.3%, 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 →
20254.52.66.4
20264.52.66.4
20274.52.66.4
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20294.52.66.4

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
Fairland2220241967
Atkinson1520241966
Pontiac1420241978
Sheffield1120241966
Minonk1120241976
Monticello1120241976
Birds1120101982
Gridley1120242001
Essex1020241969
Le Roy1020241993
Milford920231966
Sterling920232001
Newark820221969
Fairdale820242019
Compton720181968
Streator720241972
Fairbury720241976
Mackinaw620241966
Janesville620241972
Shannon620241993
Troy Grove620241993
Union620172001
Mill Creek520241966
Gulfport520232003

Vesper Sparrow Population Trend in Other States

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

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