BirdAnalyst
Species · Massachusetts · BBS 2026 Release · 1966–2025

Brown-headed Cowbird Population Trend in Massachusetts

All statesGeneralists

Brown-headed Cowbird in Massachusetts has increased: up 47% on the route-weighted index since 1968.

+47%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 →
32Routes 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 →
59YearsYears 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 MassachusettsNotable 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 Massachusetts. See the full index history below.

Brown-headed Cowbird Population Forecast in Massachusetts

If the recent trend holds, Brown-headed Cowbird in Massachusetts is projected to fall about 15% by 2030 — from 9.3 in 2025 to a central estimate of 7.9 (95% range 5.6–10). A 5-year backtest shows a typical error of ±13.6%, with 100% of held-out values landing inside the 95% band.

-15%Change by 2030TrendPercent 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 →
7.9Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
5.6–1095% 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 →
±13.6%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 Massachusetts is projected to fall about 15% by 2030 — from 9.3 in 2025 to a central estimate of 7.9 (95% range 5.6–10). A 5-year backtest shows a typical error of ±13.6%, with 100% of held-out values landing inside the 95% band.19662030
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 →
20267.85.510
20277.85.510
20287.85.510
20297.95.610
20307.95.610

Brown-headed Cowbird Survey Routes in Massachusetts

Routes recording Brown-headed Cowbird in Massachusetts.
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 →
Marion2020251966
Maynard2020251967
Belchertown2020251967
Warren1420091968
N Orange1420251968
Warren 21320252010
Mansfield1220251968
Ware River1120221993
Wellfleet 21120252016
N Oxford1020251968
Prattville820191966
Brockton820191967
Pittsfield820161967
S Barre720251968
Sheffield720221969
Gay Head720251996
Newburyport620221967
Princeton619761969
Cheshire619941969
E Pepperell519941966
Monterey520252019
Cape Cod Ns520071989
N. Andover520251995
Chilmark419831969
E Dennis320211969

Brown-headed Cowbird Population Trend in Other States

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

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.