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Species · Illinois · BBS 2026 Release · 1966–2025

Carolina Wren Population Trend in Illinois

All statesForest birds

Carolina Wren in Illinois has surged: up 289% on the route-weighted index since 1968.

+289%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 →
87Routes 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 Carolina 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 →

long arc increasecomputed 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 →

Carolina Wren has surged in Illinois: up 289% on the route-weighted index since 1968.

Carolina Wren Population Forecast in Illinois

If the recent trend holds, Carolina Wren in Illinois is projected to fall about 10% by 2030 — from 4.9 in 2025 to a central estimate of 4.4 (95% range 2.1–6.7). A 5-year backtest shows a typical error of ±93.8%, with 60% of held-out values landing inside the 95% band.

-10%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 →
4.4Projected 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 →
2.1–6.795% 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 →
±93.8%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, Carolina Wren in Illinois is projected to fall about 10% by 2030 — from 4.9 in 2025 to a central estimate of 4.4 (95% range 2.1–6.7). A 5-year backtest shows a typical error of ±93.8%, with 60% 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 →
20264.21.96.5
20274.31.96.6
20284.32.06.6
20294.42.06.7
20304.42.16.7

Carolina Wren Survey Routes in Illinois

Routes recording Carolina 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 →
Belknap4620251970
Cave In Rock3720241993
Pulaski3020251970
Belleview2420251966
Royalton2420252001
Sandusky2320231993
Bremen2020251969
Eldred1820251993
Brownville1820251993
Brnt Prairie1620251976
York1520251993
Athens1420251995
Mt Vernon1320251971
St Morgan1120221967
Beaverdam Lk1120231970
Mascoutah Lk1020251969
Bradbury920251970
Humphrey820251972
Delwood820251971
Grape Creek720252002
Karnak720252001
Olney620241968
Concord520251967
Columbia520251967
Duncan Mills520251995

Carolina Wren Population Trend in Other States

alabamaarkansasconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourinebraskanew-hampshirenew-jerseynew-yorknorth-carolinaohiooklahomapennsylvaniarhode-islandsouth-carolinatennesseetexasvermontvirginiawest-virginiawisconsin

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