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

Brown-headed Cowbird Population Trend in Delaware

All statesGeneralists

Brown-headed Cowbird in Delaware has surged: up 418% on the route-weighted index since 1968.

+418%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 →
17Routes 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 DelawareNotable 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 increasecomputed 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 surged in Delaware: up 418% on the route-weighted index since 1968.

Brown-headed Cowbird Population Forecast in Delaware

If the recent trend holds, Brown-headed Cowbird in Delaware is projected to fall about 12% by 2030 — from 20 in 2025 to a central estimate of 17 (95% range 12–23). A 5-year backtest shows a typical error of ±8.9%, with 100% of held-out values landing inside the 95% band.

-12%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 →
17Projected 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 →
12–2395% 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 →
±8.9%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 Delaware is projected to fall about 12% by 2030 — from 20 in 2025 to a central estimate of 17 (95% range 12–23). A 5-year backtest shows a typical error of ±8.9%, 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 →
2026161122
2027171122
2028171122
2029171222
2030171223

Brown-headed Cowbird Survey Routes in Delaware

Routes recording Brown-headed Cowbird in Delaware.
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 →
Frederica3320251966
Holleyville2720041966
Milton 22520252017
Harrington1820251966
Millsboro1820252017
Holleyville 21820242006
Frankford1720121966
Pepperbox 21620252017
Pepperbox1520161998
Lowes Xrds1019911966
Bethany Bch819901966
Milton820161966
Blackbird820251994
Georgetown620221992
Dover319871966
Mt Pleasant220191966
Wilmington120141968

Brown-headed Cowbird Population Trend in Other States

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

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