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

Brown-headed Cowbird Population Trend in Pennsylvania

All statesGeneralists

Brown-headed Cowbird in Pennsylvania has declined: down 38% on the route-weighted index since 1968.

-38%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 →
137Routes 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 PennsylvaniaNotable 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 Pennsylvania. See the full index history below.

Brown-headed Cowbird Population Forecast in Pennsylvania

If the recent trend holds, Brown-headed Cowbird in Pennsylvania is projected to stay roughly flat through 2029, near 5.3 (95% range 2.9–7.7). A 5-year backtest shows a typical error of ±10.3%, with 100% of held-out values landing inside the 95% band.

-7%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 →
5.3Projected 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 →
2.9–7.795% 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 →
±10.3%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 Pennsylvania is projected to stay roughly flat through 2029, near 5.3 (95% range 2.9–7.7). A 5-year backtest shows a typical error of ±10.3%, 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 →
20255.63.28.0
20265.53.18.0
20275.53.17.9
20285.43.07.8
20295.32.97.7

Brown-headed Cowbird Survey Routes in Pennsylvania

Routes recording Brown-headed Cowbird in Pennsylvania.
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 →
Big Flat3419811966
West Grove2819961966
Jacobus2820241986
Stoneybreak2520241992
Quakertown2219891970
Beaver1920241969
Mount Joy1920241978
Mill Run1820241978
Brunnerville1720091969
Chatham1620241997
Wyalusing1620241985
Ryde1520051968
Sugar Grove1520231980
Harmonsburg1420231966
Middletown1420241973
Scheafferstn1420011966
Bendersville1420241990
Plesant Grov1320241966
Sardis1319741967
Pottstown1319871966
Drehersville1319991966
Schaefferstown 21320242002
Virginia1220241969
Geeseytown1220241987
Mt Gretna 21220222002

Brown-headed Cowbird Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonrhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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