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

Black-billed Cuckoo Population Trend in Illinois

All statesGeneralists

Black-billed Cuckoo in Illinois has collapsed: down 91% on the route-weighted index since 1968.

-91%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 →
62Routes 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 →
55YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Black-billed Cuckoo 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 →

Black-billed Cuckoo has collapsed in Illinois: down 91% on the route-weighted index since 1968.

Black-billed Cuckoo Population Forecast in Illinois

If the recent trend holds, Black-billed Cuckoo in Illinois is projected to stay roughly flat through 2028, near 0.00 (95% range 0.00–0.25). A 5-year backtest shows a typical error of ±309.4%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2028TrendPercent 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 2028 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.2595% 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 →
±309.4%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, Black-billed Cuckoo in Illinois is projected to stay roughly flat through 2028, near 0.00 (95% range 0.00–0.25). A 5-year backtest shows a typical error of ±309.4%, with 100% of held-out values landing inside the 95% band.19662028
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 →
20240.000.000.25
20250.000.000.25
20260.000.000.25
20270.000.000.25
20280.000.000.25

Black-billed Cuckoo Survey Routes in Illinois

Routes recording Black-billed Cuckoo 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 →
Guilford420231973
Holcomb320081972
Geneseo320131967
Compton319731973
Mill Creek220071966
Putnam219901990
Chandlervill219731972
Deer Creek219971978
Milford220071970
Concord220111967
Rosamond219781978
Grape Creek220192019
Caledonia220161993
Seneca220212021
Cherry Val119931973
Barrington119911972
Atkinson119891982
Sheffield120041966
Buda119911977
Streator119921972
Wayne119971975
Newark119901990
Sherburnvill120191979
New Lenox119911966
Gulfport119911982

Black-billed Cuckoo Population Trend in Other States

alabamaarkansascoloradoconnecticutdelawaregeorgiaidahoindianaiowakansaskentuckymainemarylandmassachusettsmichiganminnesotamissourimontananebraskanew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniarhode-islandsouth-dakotatennesseetexasvermontvirginiawest-virginiawisconsinwyoming

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