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

Brown-headed Cowbird Population Trend in Maryland

All statesGeneralists

Brown-headed Cowbird in Maryland has increased: up 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 →
76Routes 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 MarylandNotable 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 Maryland. See the full index history below.

Brown-headed Cowbird Population Forecast in Maryland

If the recent trend holds, Brown-headed Cowbird in Maryland is projected to fall about 20% by 2030 — from 14 in 2025 to a central estimate of 11 (95% range 7.9–15). A 5-year backtest shows a typical error of ±20.5%, with 40% of held-out values landing inside the 95% band.

-20%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 →
11Projected 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 →
7.9–1595% 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 →
±20.5%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 Maryland is projected to fall about 20% by 2030 — from 14 in 2025 to a central estimate of 11 (95% range 7.9–15). A 5-year backtest shows a typical error of ±20.5%, with 40% 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 →
2026117.714
2027117.814
2028117.815
2029117.815
2030117.915

Brown-headed Cowbird Survey Routes in Maryland

Routes recording Brown-headed Cowbird in Maryland.
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 →
Honga4420251966
Island Creek4220251991
Cokesbury3920251966
Olney3520251966
Ijamsville3520251986
Williamsport3320251966
Jessup3120252013
Earlton2620242014
Madonna2520222009
La Plata2420091966
Forest Grove2420232011
Emmitsburg2220251966
Furnace Town2120252015
Nottingham2120252005
Eklo2020181966
Smithsburg1820141966
Tall Timbers1820141966
Vienna1820251966
Sinepuxent1819781966
Snow Hill1719761966
Largo1619811966
Pomonkey1620251966
Harmony1620171966
Madison1620251966
St. George'S Island1620172015

Brown-headed Cowbird Population Trend in Other States

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

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