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

Double-crested Cormorant Population Trend in Wisconsin

All statesWetland birds

Double-crested Cormorant in Wisconsin has surged: up 77% on the route-weighted index since 1978.

+77%Since 1978TrendPercent 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 →
41Routes 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 WisconsinNotable 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 Wisconsin: up 77% on the route-weighted index since 1978.

Double-crested Cormorant Population Forecast in Wisconsin

If the recent trend holds, Double-crested Cormorant in Wisconsin is projected to fall about 14% by 2029 — from 0.65 in 2024 to a central estimate of 0.56 (95% range 0.00–1.5). A 5-year backtest shows a typical error of ±74.1%, with 100% of held-out values landing inside the 95% band.

-14%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 →
0.56Projected 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 →
0.00–1.595% 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 →
±74.1%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 Wisconsin is projected to fall about 14% by 2029 — from 0.65 in 2024 to a central estimate of 0.56 (95% range 0.00–1.5). A 5-year backtest shows a typical error of ±74.1%, with 100% of held-out values landing inside the 95% band.19702029
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 →
20250.550.001.5
20260.550.001.5
20270.560.001.5
20280.560.001.5
20290.560.001.5

Double-crested Cormorant Survey Routes in Wisconsin

Routes recording Double-crested Cormorant in Wisconsin.
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 →
Hudson4620241983
Rolling Grnd2520092009
N Andover2120061987
Eden1619981998
Rolling Pr1120221997
Colby620032003
Cochrane520091995
Manawa519951995
Beloit420242024
Hebron420132013
Esdaile320011996
Phillips219931992
Mather220061995
Stratford220221986
Pt Washingtn220122012
Iron River120001992
Grand View120222022
Bayfield120082001
Dresser120241985
Union Twp120211986
Loraine120012001
Cumberland120082008
Gilman120182018
Omro 2120232008
Rib Lake119841984

Double-crested Cormorant Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawyoming

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