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

Brown-headed Cowbird Population Trend in Connecticut

All statesGeneralists

Brown-headed Cowbird in Connecticut has declined: down 33% on the route-weighted index since 1968.

-33%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 →
58YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Brown-headed Cowbird 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 →

No notable trend signals for Brown-headed Cowbird in Connecticut. See the full index history below.

Brown-headed Cowbird Population Forecast in Connecticut

If the recent trend holds, Brown-headed Cowbird in Connecticut is projected to rise about 34% by 2029 — from 5.4 in 2024 to a central estimate of 7.3 (95% range 3.2–11). A 5-year backtest shows a typical error of ±19.6%, with 100% of held-out values landing inside the 95% band.

+34%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 →
7.3Projected 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 →
3.2–1195% 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 →
±19.6%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, Brown-headed Cowbird in Connecticut is projected to rise about 34% by 2029 — from 5.4 in 2024 to a central estimate of 7.3 (95% range 3.2–11). A 5-year backtest shows a typical error of ±19.6%, with 100% of held-out values landing inside the 95% band.19662029
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 →
20257.33.211
20267.33.211
20277.33.211
20287.33.211
20297.33.211

Brown-headed Cowbird Survey Routes in Connecticut

Routes recording Brown-headed Cowbird 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 →
Willimantic3420181967
Mystic3020231973
Uncasville1420241973
Greenwich820181967
Warren820111972
Mid Haddam720241973
Southington720241973
Woodstock 2720242016
Buckingham620221966
E Hartland519921966
Woodstock520071968
Long Hill520191973
Sherman420191972
New Hartford419871972
Warren 2420242012
Granby420241988
Westbrook320241969
Danbury320231968
No Woodbury220241967
New Hartford120241994

Brown-headed Cowbird Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradodelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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