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

Field Sparrow Population Trend in Illinois

All statesForest birds

Field Sparrow in Illinois has fallen sharply: down 58% on the route-weighted index since 1968.

-58%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 →
104Routes 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 Field 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 →

long arc declinecomputed 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 →

Field Sparrow has fallen sharply in Illinois: down 58% on the route-weighted index since 1968.

Field Sparrow Population Forecast in Illinois

If the recent trend holds, Field Sparrow in Illinois is projected to fall about 55% by 2030 — from 4.8 in 2025 to a central estimate of 2.1 (95% range 0.00–6.3). A 5-year backtest shows a typical error of ±62.9%, with 80% of held-out values landing inside the 95% band.

-55%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 →
2.1Projected 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 →
0.00–6.395% 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 →
±62.9%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, Field Sparrow in Illinois is projected to fall about 55% by 2030 — from 4.8 in 2025 to a central estimate of 2.1 (95% range 0.00–6.3). A 5-year backtest shows a typical error of ±62.9%, with 80% 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 →
20262.70.006.8
20272.60.006.7
20282.40.006.6
20292.30.006.4
20302.10.006.3

Field Sparrow Survey Routes in Illinois

Routes recording Field 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 →
Beaverdam Lk3120231970
Brownville2920251993
Guilford2520231967
Belknap2420251970
Royalton2220252001
Bremen1920251969
Sandusky1820231993
Brnt Prairie1720251976
Pulaski1720251970
Robinson1720231970
Kell1520252001
Fairbury1420251976
Karnak1420252001
Melrose1319991973
Bradbury1320251970
Cave In Rock1320241993
Belleview1220251966
Lake Galena1220212001
Janesville1020251972
Dudleyville1020252001
Mt Vernon920251971
Putnam820231967
Birds820241976
Delwood820251970
Marshall820252001

Field Sparrow Population Trend in Other States

alabamaarkansascoloradoconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawest-virginiawisconsinwyoming

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