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

Brown-headed Cowbird Population Trend in Maine

All statesGeneralists

Brown-headed Cowbird in Maine has collapsed: down 81% on the route-weighted index since 1968.

-81%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 →
68Routes 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 MaineNotable 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 →

Brown-headed Cowbird has collapsed in Maine: down 81% on the route-weighted index since 1968.

Brown-headed Cowbird Population Forecast in Maine

If the recent trend holds, Brown-headed Cowbird in Maine is projected to fall about 100% by 2029 — from 1.9 in 2024 to a central estimate of 0.00 (95% range 0.00–2.4). A 5-year backtest shows a typical error of ±150.6%, with 60% of held-out values landing inside the 95% band.

-100%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 →
0.00Projected 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 →
0.00–2.495% 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 →
±150.6%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 Maine is projected to fall about 100% by 2029 — from 1.9 in 2024 to a central estimate of 0.00 (95% range 0.00–2.4). A 5-year backtest shows a typical error of ±150.6%, with 60% 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 →
20250.000.002.4
20260.000.002.4
20270.000.002.4
20280.000.002.4
20290.000.002.4

Brown-headed Cowbird Survey Routes in Maine

Routes recording Brown-headed Cowbird in Maine.
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 →
Benton2219801972
Warren1019901973
Kittery Pt920241966
Manchester919951971
Otisfield Gr820151966
Topsfield719961978
Cape Neddick620241972
Turner520101972
Northfield519811976
Turner 2520242012
Freedom420211973
Harmony420241967
Carrying Pl420021980
Washburn420051979
Ft Fairfield420051993
St David420051982
Westbrook320241977
Biddeford320191974
Bowdoin Ctr320211971
Hancock320121969
Winn320181969
Clayton Lake319771977
Cornville320242012
Searsport320242002
Church Hill320141991

Brown-headed Cowbird Population Trend in Other States

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

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