BirdAnalyst
Species · Pennsylvania · BBS 2025 Release · 1966–2024

Double-crested Cormorant Population Trend in Pennsylvania

All statesWetland birds

Double-crested Cormorant in Pennsylvania has held roughly steady: down 1% on the route-weighted index since 1991.

-1%Since 1991TrendPercent 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 →
31Routes 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 →
30YearsYears 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 PennsylvaniaNotable 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 Pennsylvania. See the full index history below.

Double-crested Cormorant Population Forecast in Pennsylvania

If the recent trend holds, Double-crested Cormorant in Pennsylvania is projected to fall about 26% by 2029 — from 0.09 in 2024 to a central estimate of 0.07 (95% range 0.00–0.15). A 5-year backtest shows a typical error of ±469.2%, with 100% of held-out values landing inside the 95% band.

-26%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 →
0.07Projected 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 →
0.00–0.1595% 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 →
±469.2%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, Double-crested Cormorant in Pennsylvania is projected to fall about 26% by 2029 — from 0.09 in 2024 to a central estimate of 0.07 (95% range 0.00–0.15). A 5-year backtest shows a typical error of ±469.2%, with 100% of held-out values landing inside the 95% band.19732029
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 →
20250.060.000.15
20260.070.000.15
20270.070.000.15
20280.070.000.15
20290.070.000.15

Double-crested Cormorant Survey Routes in Pennsylvania

Routes recording Double-crested Cormorant in Pennsylvania.
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 →
Canadensis1320152015
Arnot1020122000
Rosecrans820031999
Brunnerville820091973
Rush720242001
Mount Joy320112011
Brick Tavern320122012
Middletown320141998
Greentown220141991
Brunnerville 2220172010
Espyville120232002
Whig Hill120152015
Berwick120012000
Teepleville119921992
N Washington120222022
Lovelton120182018
Pottersdale120142002
Leola120242024
Ramsey119941994
Mawr Glen120082008
Landisburg120182002
Beaver120182009
Parkwood120162016
Schaefferstown 2120142014
Kaylor120162016

Double-crested Cormorant Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonrhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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