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

Field Sparrow Population Trend in Illinois

All statesGeneralists

Field Sparrow in Illinois has fallen sharply: down 57% on the route-weighted index since 1968.

-57%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 →
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 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 57% 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 61% by 2029 — from 5.4 in 2024 to a central estimate of 2.1 (95% range 0.00–6.3). A 5-year backtest shows a typical error of ±61.4%, with 80% of held-out values landing inside the 95% band.

-61%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 →
2.1Projected 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 →
0.00–6.395% 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 →
±61.4%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, Field Sparrow in Illinois is projected to fall about 61% by 2029 — from 5.4 in 2024 to a central estimate of 2.1 (95% range 0.00–6.3). A 5-year backtest shows a typical error of ±61.4%, with 80% 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 →
20252.70.006.8
20262.50.006.7
20272.40.006.5
20282.30.006.4
20292.10.006.3

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 →
Royalton4520242001
Beaverdam Lk3120231970
Belknap3020241970
Guilford2520231967
Bremen2520241969
Sandusky1820231993
Kell1820242001
Robinson1720231970
Brownville1720241993
Brnt Prairie1520241976
Pulaski1520241970
Dudleyville1420242001
Melrose1319991973
Cave In Rock1320241993
Belleview1220241966
Lake Galena1220212001
Bradbury1120241970
Marshall1120242001
Delwood1020241970
Mt Vernon920241971
Karnak920242001
Putnam820231967
Birds820241976
Martinsville720241970
Geneseo620211967

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 2026-05-22.