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

Marsh Wren Population Trend in Illinois

All statesForest birds

Marsh Wren in Illinois has declined: down 34% on the route-weighted index since 1979.

-34%Since 1979TrendPercent 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 →
13Routes 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 →
23YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Marsh Wren 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 Marsh Wren in Illinois. See the full index history below.

Marsh Wren Population Forecast in Illinois

If the recent trend holds, Marsh Wren in Illinois is projected to fall about 92% by 2030 — from 0.13 in 2025 to a central estimate of 0.01 (95% range 0.00–0.08). A 5-year backtest shows a typical error of ±133.6%, with 80% of held-out values landing inside the 95% band.

-92%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 →
0.01Projected 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 →
0.00–0.0895% 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 →
±133.6%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, Marsh Wren in Illinois is projected to fall about 92% by 2030 — from 0.13 in 2025 to a central estimate of 0.01 (95% range 0.00–0.08). A 5-year backtest shows a typical error of ±133.6%, with 80% of held-out values landing inside the 95% band.19762030
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 →
20260.020.000.09
20270.010.000.08
20280.010.000.08
20290.010.000.08
20300.010.000.08

Marsh Wren Survey Routes in Illinois

Routes recording Marsh Wren 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 →
Compton620252000
New Lenox419821977
Melrose319791979
Barrington320111977
Alden220252025
Athensville120252025
Wayne120241985
Sherburnvill120162016
Gulfport120252025
Chandlervill119851976
Sterling120092009
Clayton120182016
Bartonville120192019

Marsh Wren Population Trend in Other States

alabamaarizonacaliforniacoloradoconnecticutdelawarefloridageorgiaidahoindianaiowakansaslouisianamainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiooregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatexasutahvermontvirginiawashingtonwisconsinwyoming

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