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Species · Massachusetts · BBS 2025 Release · 1966–2024

Double-crested Cormorant Population Trend in Massachusetts

All statesWetland birds

Double-crested Cormorant in Massachusetts has surged: up 100% on the route-weighted index since 1971.

+100%Since 1971TrendPercent 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 →
23Routes 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 →
47YearsYears 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 MassachusettsNotable 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 →

Double-crested Cormorant has surged in Massachusetts: up 100% on the route-weighted index since 1971.

Double-crested Cormorant Population Forecast in Massachusetts

If the recent trend holds, Double-crested Cormorant in Massachusetts is projected to rise about 516% by 2029 — from 0.07 in 2024 to a central estimate of 0.41 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±180.5%, with 100% of held-out values landing inside the 95% band.

+516%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 →
0.41Projected 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 →
0.00–1.495% 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 →
±180.5%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 Massachusetts is projected to rise about 516% by 2029 — from 0.07 in 2024 to a central estimate of 0.41 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±180.5%, with 100% of held-out values landing inside the 95% band.19692029
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 →
20250.430.001.5
20260.420.001.5
20270.420.001.4
20280.420.001.4
20290.410.001.4

Double-crested Cormorant Survey Routes in Massachusetts

Routes recording Double-crested Cormorant in Massachusetts.
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 →
Chilmark2219831969
Hancock1220132013
Newburyport1120221980
Littleton920002000
Cape Cod Ns519961992
Brockton420181986
Chesterfield420132013
Wellfleet 2320192019
Marion220231970
Maynard220061998
E Pepperell219921990
Gay Head220211996
N. Andover220181995
E Dennis120191996
Wellfleet119981992
Prattville120061977
N Oxford120172017
Mansfield120211998
Belchertown120012001
Warren120082004
N Orange120242024
Holden120091988
Warren 2120212016

Double-crested Cormorant Population Trend in Other States

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

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