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

Least Flycatcher Population Trend in Illinois

All statesAerial insectivores

Least Flycatcher in Illinois has collapsed: down 82% on the route-weighted index since 1970.

-82%Since 1970TrendPercent 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 →
30Routes 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 →
30YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Least Flycatcher 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 declinecomputed 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 →

Least Flycatcher has collapsed in Illinois: down 82% on the route-weighted index since 1970.

Least Flycatcher Population Forecast in Illinois

If the recent trend holds, Least Flycatcher in Illinois is projected to stay roughly flat through 2027, near 0.00 (95% range 0.00–0.04). A 5-year backtest shows a typical error of ±144.6%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2027TrendPercent 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 →
0.00Projected 2027 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.0495% 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 →
±144.6%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, Least Flycatcher in Illinois is projected to stay roughly flat through 2027, near 0.00 (95% range 0.00–0.04). A 5-year backtest shows a typical error of ±144.6%, with 100% of held-out values landing inside the 95% band.19672027
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 →
20230.000.000.04
20240.000.000.04
20250.000.000.04
20260.000.000.04
20270.000.000.04

Least Flycatcher Survey Routes in Illinois

Routes recording Least Flycatcher 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 →
Chandlervill220021971
Martinsville219831983
Alden220192019
Guilford120012001
Mill Creek119841984
Holcomb119831983
Barrington119671967
Itasca119971993
Geneseo120171991
Streator119741974
Wayne120122012
Sherburnvill119671967
New Lenox119821969
Williamsfld120112011
Deer Creek120012001
Mackinaw119711971
Dailey120032003
Milford120011970
Melrose119941994
Bluff Spgs119711971
Concord119951995
Belleview120052005
Fairland119951995
Humboldt119701970
Keithsburg120142014

Least Flycatcher Population Trend in Other States

alaskaarkansascaliforniacoloradoconnecticutgeorgiaidahoindianaiowakentuckymainemarylandmassachusettsmichiganminnesotamissourimontananebraskanew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiooregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseeutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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