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

Brown-headed Cowbird Population Trend in New Hampshire

All statesGeneralists

Brown-headed Cowbird in New Hampshire has fallen sharply: down 62% on the route-weighted index since 1968.

-62%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 →
25Routes 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 HampshireNotable 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 declinecomputed 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 fallen sharply in New Hampshire: down 62% on the route-weighted index since 1968.

Brown-headed Cowbird Population Forecast in New Hampshire

If the recent trend holds, Brown-headed Cowbird in New Hampshire is projected to fall about 43% by 2029 — from 2.3 in 2024 to a central estimate of 1.3 (95% range 0.00–3.3). A 5-year backtest shows a typical error of ±39.3%, with 80% of held-out values landing inside the 95% band.

-43%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 →
1.3Projected 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 →
0.00–3.395% 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 →
±39.3%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 New Hampshire is projected to fall about 43% by 2029 — from 2.3 in 2024 to a central estimate of 1.3 (95% range 0.00–3.3). A 5-year backtest shows a typical error of ±39.3%, with 80% 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 →
20251.70.003.8
20261.60.003.7
20271.50.003.6
20281.40.003.4
20291.30.003.3

Brown-headed Cowbird Survey Routes in New Hampshire

Routes recording Brown-headed Cowbird in New Hampshire.
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 →
Dover920241966
Strafford920241966
Concord820241966
Gilmantn I W620241969
Brentwood419981966
Dixvil Notch419921966
Fitzwilliam320241966
Canterbury320241966
Marlow320241966
Clarksville320001966
Peterborough220241966
Epsom220231966
Lempster220241966
Crawford Not219751967
Hopkinton120241966
Wilmot120241966
Mt Chocorua120241966
Walpole120241966
Jefferson Hl120231966
Franconia120171966
Milan120241966
Stratford120041966
Glen120231975
East Kingston120221999
Jeffers Ntch119981998

Brown-headed Cowbird Population Trend in Other States

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

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