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Species · California · BBS 2025 Release · 1966–2024

Brandt's Cormorant Population Trend in California

All statesWetland birds

Brandt's Cormorant in California has surged: up 109% on the route-weighted index since 1972.

+109%Since 1972TrendPercent 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 →
10Routes 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 →
49YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Brandt's 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 →

Brandt's Cormorant has surged in California: up 109% on the route-weighted index since 1972.

Brandt's Cormorant Population Forecast in California

If the recent trend holds, Brandt's Cormorant in California is projected to fall about 86% by 2029 — from 0.63 in 2024 to a central estimate of 0.09 (95% range 0.00–1.1). A 5-year backtest shows a typical error of ±94.6%, with 80% of held-out values landing inside the 95% band.

-86%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 →
0.09Projected 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 →
0.00–1.195% 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 →
±94.6%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, Brandt's Cormorant in California is projected to fall about 86% by 2029 — from 0.63 in 2024 to a central estimate of 0.09 (95% range 0.00–1.1). A 5-year backtest shows a typical error of ±94.6%, with 80% of held-out values landing inside the 95% band.19682029
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 →
20250.110.001.1
20260.110.001.1
20270.100.001.1
20280.100.001.1
20290.090.001.1

Brandt's Cormorant Survey Routes in California

Routes recording Brandt's 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 →
S Catalina13420192013
Harbor Lake 25920242014
Bodega Bay2320171974
Poway619801980
Harbor Lake419801978
Fish Rock320131973
Fairfax320171978
Navarro219801979
Crescent Cty119821982
Honeydew120171968

Brandt's Cormorant Population Trend in Other States

oregonwashington

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