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

Black-billed Cuckoo Population Trend in Connecticut

All statesGeneralists

Black-billed Cuckoo in Connecticut has fallen sharply: down 71% on the route-weighted index since 1968.

-71%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 →
20Routes 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 →
48YearsYears 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 ConnecticutNotable 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 fallen sharply in Connecticut: down 71% on the route-weighted index since 1968.

Black-billed Cuckoo Population Forecast in Connecticut

If the recent trend holds, Black-billed Cuckoo in Connecticut is projected to fall about 100% by 2028 — from 0.36 in 2023 to a central estimate of 0.00 (95% range 0.00–2.7). A 5-year backtest shows a typical error of ±392%, with 100% of held-out values landing inside the 95% band.

-100%Change 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 →
0.00–2.795% 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 →
±392%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 Connecticut is projected to fall about 100% by 2028 — from 0.36 in 2023 to a central estimate of 0.00 (95% range 0.00–2.7). A 5-year backtest shows a typical error of ±392%, 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 →
20240.000.002.7
20250.000.002.7
20260.000.002.7
20270.000.002.7
20280.000.002.7

Black-billed Cuckoo Survey Routes in Connecticut

Routes recording Black-billed Cuckoo in Connecticut.
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 →
Warren320051972
Mystic220191973
Buckingham220161966
No Woodbury220051967
New Hartford220191994
E Hartland119921966
Uncasville120231973
Woodstock119861968
Westbrook120171970
Willimantic120141967
Sherman120141972
Greenwich119971967
Danbury120121968
Long Hill119821972
Mid Haddam120191973
Southington120231974
New Hartford119871972
Woodstock 2120232017
Warren 2120232015
Granby120221988

Black-billed Cuckoo Population Trend in Other States

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

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