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

Double-crested Cormorant Population Trend in Delaware

All statesWetland birds

Double-crested Cormorant in Delaware has surged: up 80% on the route-weighted index since 1975.

+80%Since 1975TrendPercent 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 →
13Routes 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 →
38YearsYears 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 DelawareNotable 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 Delaware: up 80% on the route-weighted index since 1975.

Double-crested Cormorant Population Forecast in Delaware

If the recent trend holds, Double-crested Cormorant in Delaware is projected to rise about 194% by 2028 — from 0.50 in 2023 to a central estimate of 1.5 (95% range 0.00–3.5). A 5-year backtest shows a typical error of ±372.8%, with 100% of held-out values landing inside the 95% band.

+194%Change by 2028TrendPercent 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 →
1.5Projected 2028 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–3.595% 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 →
±372.8%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 Delaware is projected to rise about 194% by 2028 — from 0.50 in 2023 to a central estimate of 1.5 (95% range 0.00–3.5). A 5-year backtest shows a typical error of ±372.8%, with 100% of held-out values landing inside the 95% band.19662028
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 →
20241.40.003.4
20251.40.003.4
20261.40.003.4
20271.40.003.4
20281.50.003.5

Double-crested Cormorant Survey Routes in Delaware

Routes recording Double-crested Cormorant in Delaware.
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 →
Frederica620072007
Bethany Bch419901973
Lowes Xrds319861978
Milton320021996
Mt Pleasant220162005
Wilmington220131987
Holleyville220031998
Georgetown220031997
Pepperbox 2220232017
Harrington120211966
Blackbird120211999
Millsboro120192019
Pepperbox120161998

Double-crested Cormorant Population Trend in Other States

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

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