BirdAnalyst
Species · New Jersey · BBS 2025 Release · 1966–2024

Brown-headed Cowbird Population Trend in New Jersey

All statesGeneralists

Brown-headed Cowbird in New Jersey has surged: up 168% on the route-weighted index since 1968.

+168%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 →
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 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 168% 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 32% by 2029 — from 8.2 in 2024 to a central estimate of 11 (95% range 6.6–15). A 5-year backtest shows a typical error of ±60.5%, with 40% of held-out values landing inside the 95% band.

+32%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 →
6.6–1595% 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 →
±60.5%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 New Jersey is projected to rise about 32% by 2029 — from 8.2 in 2024 to a central estimate of 11 (95% range 6.6–15). A 5-year backtest shows a typical error of ±60.5%, with 40% 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 →
2025106.115
2026116.215
2027116.415
2028116.515
2029116.615

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
Pomona2020241978
Woodbury Hgt1720241967
Hope1719941970
Spraguetown 31720242023
Croton 21320242008
Cape May Ch1220131992
Bloomsbury1120241969
Dover1120231977
Toms River1020241966
Bennett Mill1020001966
High Point1020241977
Pottersville1020241977
Del Haven1019911991
Winslow1020241989
Ramseysburg1020241995
Pedricktown920121991
Ancora819771966
Keyport820221990
Friendship820241977
Estell Manor820222021
Bennett Mill 2820242016
Pedricktown 2720242013

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 2026-05-22.