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

Brown-headed Cowbird Population Trend in Maryland

All statesGeneralists

Brown-headed Cowbird in Maryland has increased: up 37% on the route-weighted index since 1968.

+37%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 →
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 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 stay roughly flat through 2029, near 11 (95% range 7.7–14). A 5-year backtest shows a typical error of ±15.3%, with 60% of held-out values landing inside the 95% band.

-8%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 →
11Projected 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 →
7.7–1495% 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 →
±15.3%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 stay roughly flat through 2029, near 11 (95% range 7.7–14). A 5-year backtest shows a typical error of ±15.3%, 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 →
2025117.514
2026117.614
2027117.614
2028117.614
2029117.714

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 →
Olney4420241966
Madison3420241966
Cokesbury3420241966
Island Creek2720241991
Earlton2620242014
Madonna2520222009
La Plata2420091966
Forest Grove2420232011
Eklo2020181966
Davidsnville2020241982
Williamsport1920241966
Smithsburg1820141966
Tall Timbers1820141966
Sinepuxent1819781966
Millington1720241966
Snow Hill1719761966
Ijamsville1720241986
Largo1619811966
Harmony1620171966
St. George'S Island1620172015
Emmitsburg1520241966
Piney Neck1520241966
Newark1420241966
Potomac Park1320241970
Honga1320241966

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 2026-05-22.