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

Swamp Sparrow Population Trend in Illinois

All statesWetland birds

Swamp Sparrow in Illinois has declined: down 43% on the route-weighted index since 1974.

-43%Since 1974TrendPercent 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 →
21Routes 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 →
53YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Swamp 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 Swamp Sparrow in Illinois. See the full index history below.

Swamp Sparrow Population Forecast in Illinois

If the recent trend holds, Swamp Sparrow in Illinois is projected to stay roughly flat through 2030, near 0.03 (95% range 0.00–0.09). A 5-year backtest shows a typical error of ±64.2%, with 80% of held-out values landing inside the 95% band.

n/aChange 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 →
0.03Projected 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 →
0.00–0.0995% 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 →
±64.2%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, Swamp Sparrow in Illinois is projected to stay roughly flat through 2030, near 0.03 (95% range 0.00–0.09). A 5-year backtest shows a typical error of ±64.2%, with 80% of held-out values landing inside the 95% band.19722030
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 →
20260.030.000.10
20270.030.000.10
20280.030.000.10
20290.030.000.09
20300.030.000.09

Swamp Sparrow Survey Routes in Illinois

Routes recording Swamp 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 →
Milford619961989
Guilford119741974
Mill Creek120001972
Holcomb119981978
Cherry Val120001972
Barrington119971978
Itasca120122012
Atkinson120062006
Sheffield119741974
Compton120251980
Wayne120251981
Sherburnvill119921992
New Lenox119991976
Chandlervill119741974
Lake Summerset120252008
Union120122012
Mt Vernon120052005
Caledonia119961993
Troy Grove120152015
York120032003
Alden120232023

Swamp Sparrow Population Trend in Other States

connecticutdelawareindianaiowamainemarylandmassachusettsmichiganminnesotanebraskanew-hampshirenew-jerseynew-yorknorth-dakotaohiopennsylvaniarhode-islandsouth-dakotavermontvirginiawest-virginiawisconsin

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