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

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 →
56YearsYears 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 stay roughly flat through 2029, near 1.2 (95% range 0.83–1.6). A 5-year backtest shows a typical error of ±29.2%, with 40% of held-out values landing inside the 95% band.

-0%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 →
1.2Projected 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 →
0.83–1.695% 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 →
±29.2%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, Northern Parula in Illinois is projected to stay roughly flat through 2029, near 1.2 (95% range 0.83–1.6). A 5-year backtest shows a typical error of ±29.2%, with 40% of held-out values landing inside the 95% band.19672029
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 →
20251.10.741.6
20261.20.761.6
20271.20.791.6
20281.20.811.6
20291.20.831.6

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
Bremen1620241969
Sandusky1520231993
Pulaski1420241973
Belknap1320241974
Belleview1020241967
Delwood720241978
York620241999
Royalton420242002
Cave In Rock420241993
St Morgan320221984
Karnak320242003
Athens220242022
Clayton220232009
Grape Creek220242007
Melrose219981973
Jamestown220172005
Beaucoup220241972
Olney220161978
Brownville220242002
Payson120182004
Sheffield120171987
Waynesville120032003
Newark120172009
Gulfport120091981

Northern Parula Population Trend in Other States

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

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.