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

Northern Parula Population Trend in Illinois

All statesForest birds

Northern Parula in Illinois has surged: up 27× on the route-weighted index since 1969.

27×Since 1969TrendPercent 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 →
57Routes 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 →
57YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Northern Parula 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 →

Northern Parula has surged in Illinois: up 27× on the route-weighted index since 1969.

Northern Parula Population Forecast in Illinois

If the recent trend holds, Northern Parula in Illinois is projected to fall about 14% by 2030 — from 1.5 in 2025 to a central estimate of 1.3 (95% range 0.88–1.7). A 5-year backtest shows a typical error of ±35.5%, with 20% of held-out values landing inside the 95% band.

-14%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 →
1.3Projected 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 →
0.88–1.795% 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 →
±35.5%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, Northern Parula in Illinois is projected to fall about 14% by 2030 — from 1.5 in 2025 to a central estimate of 1.3 (95% range 0.88–1.7). A 5-year backtest shows a typical error of ±35.5%, with 20% of held-out values landing inside the 95% band.19672030
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 →
20261.20.781.6
20271.20.811.6
20281.20.831.7
20291.30.851.7
20301.30.881.7

Northern Parula Survey Routes in Illinois

Routes recording Northern Parula 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 Lk1920231970
Bremen1620251969
Belknap1620251974
Sandusky1520231993
Royalton1420252002
Belleview1320251967
Pulaski1020251973
Delwood820251978
York620251999
Bradbury420251993
Brnt Prairie420251994
Cave In Rock420241993
Athens320252022
Grape Creek320252007
St Morgan320221984
Karnak320242003
Melrose219981973
Jamestown220172005
Olney220161978
Eldred220251996
Brownville220252002
Payson120182004
Clayton120252009
Sheffield120171987
Waynesville120032003

Northern Parula Population Trend in Other States

alabamaarkansascaliforniaconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourinebraskanew-hampshirenew-jerseynew-yorknorth-carolinaohiooklahomapennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawest-virginiawisconsin

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