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Species · Maryland · BBS 2025 Release · 1966–2024

Double-crested Cormorant Population Trend in Maryland

All statesWetland birds

Double-crested Cormorant in Maryland has surged: up 683% on the route-weighted index since 1981.

+683%Since 1981TrendPercent 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 →
40Routes 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 →
42YearsYears 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 MarylandNotable 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 Maryland: up 683% on the route-weighted index since 1981.

Double-crested Cormorant Population Forecast in Maryland

If the recent trend holds, Double-crested Cormorant in Maryland is projected to rise about 939% by 2029 — from 0.07 in 2024 to a central estimate of 0.74 (95% range 0.00–1.6). A 5-year backtest shows a typical error of ±262.7%, with 80% of held-out values landing inside the 95% band.

+939%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 →
0.74Projected 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 →
0.00–1.695% 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 →
±262.7%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 Maryland is projected to rise about 939% by 2029 — from 0.07 in 2024 to a central estimate of 0.74 (95% range 0.00–1.6). A 5-year backtest shows a typical error of ±262.7%, with 80% of held-out values landing inside the 95% band.19722029
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 →
20250.710.001.6
20260.710.001.6
20270.720.001.6
20280.730.001.6
20290.740.001.6

Double-crested Cormorant Survey Routes in Maryland

Routes recording Double-crested Cormorant in Maryland.
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 →
Madison5620231988
Pomfret3019981985
St. George'S Island2520172015
Hughesville2020092009
Northeast2020081972
Upper Xrds1320051995
Oldtown320212021
Grove Neck319931993
Wolfsville320052005
Eklo320082007
Tall Timbers320041988
Cokesbury320222013
Finzel320142014
Olney220191995
Pomonkey220092003
Theodore220161992
Vienna220101991
Ijamsville220132013
Potomac Park120172017
Williamsport120182017
Emmitsburg120242024
Van Bibber120022002
Berlin120101990
Indiantown120022002
Earlton120182018

Double-crested Cormorant Population Trend in Other States

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

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