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

Double-crested Cormorant Population Trend in Connecticut

All statesWetland birds

Double-crested Cormorant in Connecticut has fallen sharply: down 55% on the route-weighted index since 1981.

-55%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 →
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 →
34YearsYears 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 ConnecticutNotable 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 declinecomputed 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 fallen sharply in Connecticut: down 55% on the route-weighted index since 1981.

Double-crested Cormorant Population Forecast in Connecticut

If the recent trend holds, Double-crested Cormorant in Connecticut is projected to rise about 16% by 2029 — from 0.11 in 2024 to a central estimate of 0.13 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±41.7%, with 100% of held-out values landing inside the 95% band.

+16%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 →
0.13Projected 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 →
±41.7%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 Connecticut is projected to rise about 16% by 2029 — from 0.11 in 2024 to a central estimate of 0.13 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±41.7%, with 100% of held-out values landing inside the 95% band.19792029
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 →
20250.190.001.4
20260.180.001.4
20270.160.001.4
20280.140.001.4
20290.130.001.4

Double-crested Cormorant Survey Routes in Connecticut

Routes recording Double-crested Cormorant in Connecticut.
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 →
New Hartford1119861986
Danbury720131988
New Hartford420032003
Mid Haddam420221988
Uncasville320232022
Mystic220221979
Woodstock 2220182018
Southington220062006
Westbrook120241979
Willimantic120171990
Sherman120062001
Greenwich120181991

Double-crested Cormorant Population Trend in Other States

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