BirdAnalyst
Species · New Jersey · BBS 2026 Release · 1966–2025

Brown-headed Cowbird Population Trend in New Jersey

All statesGeneralists

Brown-headed Cowbird in New Jersey has surged: up 156% on the route-weighted index since 1968.

+156%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 →
43Routes 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 New JerseyNotable 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 New Jersey: up 156% on the route-weighted index since 1968.

Brown-headed Cowbird Population Forecast in New Jersey

If the recent trend holds, Brown-headed Cowbird in New Jersey is projected to rise about 82% by 2030 — from 5.8 in 2025 to a central estimate of 11 (95% range 6.2–15). A 5-year backtest shows a typical error of ±63.2%, with 40% of held-out values landing inside the 95% band.

+82%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 →
6.2–1595% 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 →
±63.2%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 New Jersey is projected to rise about 82% by 2030 — from 5.8 in 2025 to a central estimate of 11 (95% range 6.2–15). A 5-year backtest shows a typical error of ±63.2%, 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 →
2026105.815
2027105.915
2028106.015
2029116.115
2030116.215

Brown-headed Cowbird Survey Routes in New Jersey

Routes recording Brown-headed Cowbird in New Jersey.
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 →
Holmansville2220091969
Croton2120071970
Spraguetown 22120072000
Hope1719941970
Pomona1420251978
Spraguetown 31420252023
Cape May Ch1220131992
Dover1120231977
Toms River1020241966
Bennett Mill1020001966
Pottersville1020241977
Del Haven1019911991
Pedricktown920121991
Six Points820251978
Ancora819771966
Keyport820221990
Pedricktown 2820252013
Woodbury Hgt720251967
Winslow720251989
Bennett Mill 2720252016
Croton 2620252008
Albion520221967
Kemah Lake520241967
High Point520251977
Friendship520251977

Brown-headed Cowbird Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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