BirdAnalyst
Species · California · BBS 2026 Release · 1966–2025

Double-crested Cormorant Population Trend in California

All statesWetland birds

Double-crested Cormorant in California has risen sharply: up 67% on the route-weighted index since 1974.

+67%Since 1974TrendPercent 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 →
74Routes 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 →
53YearsYears 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 CaliforniaNotable 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 risen sharply in California: up 67% on the route-weighted index since 1974.

Double-crested Cormorant Population Forecast in California

If the recent trend holds, Double-crested Cormorant in California is projected to rise about 20× by 2030 — from 0.15 in 2025 to a central estimate of 3.0 (95% range 0.00–6.0). A 5-year backtest shows a typical error of ±3527.6%, with 0% of held-out values landing inside the 95% band.

20×Change by 2030TrendPercent 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 →
3.0Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–6.095% 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 →
±3527.6%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 California is projected to rise about 20× by 2030 — from 0.15 in 2025 to a central estimate of 3.0 (95% range 0.00–6.0). A 5-year backtest shows a typical error of ±3527.6%, with 0% of held-out values landing inside the 95% band.19722030
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 →
20262.90.005.9
20272.90.005.9
20282.90.006.0
20293.00.006.0
20303.00.006.0

Double-crested Cormorant Survey Routes in California

Routes recording Double-crested Cormorant in California.
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 →
Dorris7220191972
Cedarville6020242024
Fairfax3220241972
Iron Gate2720191988
Arvin2720212013
Hughson1820242000
Hat Creek1219871987
Eagle Lake820072002
Honeydew720161977
Hollister720071995
Creston620142014
Moraga520241998
Ingalls519981974
Genesee420152008
Downieville420072007
Oneals420002000
Point Reyes420082007
Mesa Grande420102010
Buena Vista420192019
Nubieber319931977
Red Bluff320031987
Lockwood320022000
Crescent Cty220221974
Pennington220192004
Riovista220181972

Double-crested Cormorant Population Trend in Other States

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

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.