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

Double-crested Cormorant Population Trend in New Hampshire

All statesWetland birds

Double-crested Cormorant in New Hampshire has held roughly steady: down 6% on the route-weighted index since 1982.

-6%Since 1982TrendPercent 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 →
12Routes 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 →
35YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Double-crested Cormorant 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 →

No notable trend signals for Double-crested Cormorant in New Hampshire. See the full index history below.

Double-crested Cormorant Population Forecast in New Hampshire

If the recent trend holds, Double-crested Cormorant in New Hampshire is projected to stay roughly flat through 2029, near 0.07 (95% range 0.00–0.27). A 5-year backtest shows a typical error of ±41.5%, with 80% of held-out values landing inside the 95% band.

n/aChange 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 →
0.07Projected 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 →
0.00–0.2795% 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 →
±41.5%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, Double-crested Cormorant in New Hampshire is projected to stay roughly flat through 2029, near 0.07 (95% range 0.00–0.27). A 5-year backtest shows a typical error of ±41.5%, with 80% of held-out values landing inside the 95% band.19742029
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 →
20250.070.000.28
20260.070.000.28
20270.070.000.28
20280.070.000.27
20290.070.000.27

Double-crested Cormorant Survey Routes in New Hampshire

Routes recording Double-crested Cormorant 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 →
Peterborough619751975
Dover320181982
Milan320232002
Marlow219921992
Epsom120241989
Strafford120232011
Mt Chocorua120212021
Walpole120142014
Lempster119991999
Jefferson Hl120171987
Dixvil Notch120162016
Clarksville119741974

Double-crested Cormorant Population Trend in Other States

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

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