BirdAnalyst
Species · BCR 32 · BBS 2025 Release · 1966–2024

Double-crested Cormorant In Coastal California

All regionsCoastal CaliforniaWetland birds

Double-crested Cormorant in Coastal California has surged: up 599% on the route-weighted index since 1974.

+599%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 →
40Routes In RegionSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
50YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable SignalsNotable 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 Coastal California: up 599% on the route-weighted index since 1974.

Forecast

If the recent trend holds, Double-crested Cormorant in Coastal California is projected to fall about 18% by 2029 — from 1.6 in 2024 to a central estimate of 1.3 (95% range 0.02–2.6). A 5-year backtest shows a typical error of ±516.9%, with 80% of held-out values landing inside the 95% band.

-18%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 →
1.3Projected 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 →
0.02–2.695% 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 →
±516.9%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 Coastal California is projected to fall about 18% by 2029 — from 1.6 in 2024 to a central estimate of 1.3 (95% range 0.02–2.6). A 5-year backtest shows a typical error of ±516.9%, with 80% of held-out values landing inside the 95% band.19722029
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 →
20251.20.002.5
20261.30.002.6
20271.30.002.6
20281.30.002.6
20291.30.022.6

Routes In Coastal California

Routes recording Double-crested Cormorant in Coastal 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 →
FairfaxCALIFORNIA322024
ArvinCALIFORNIA272021
HughsonCALIFORNIA182024
WestleyCALIFORNIA102024
HollisterCALIFORNIA72007
Staten Is.CALIFORNIA72024
CrestonCALIFORNIA62014
MoragaCALIFORNIA52024
Point ReyesCALIFORNIA42008
Mesa GrandeCALIFORNIA42010
OnealsCALIFORNIA42000
Buena VistaCALIFORNIA42019
Red BluffCALIFORNIA32003
LockwoodCALIFORNIA32002
CoyoteCALIFORNIA32024
PenningtonCALIFORNIA22019
RiovistaCALIFORNIA22018
San YsidroCALIFORNIA21986
SangerCALIFORNIA22015
OrovilleCALIFORNIA22012
CopperopolisCALIFORNIA22016
TracyCALIFORNIA21993
PolomaCALIFORNIA22022
Harbor LakeCALIFORNIA11985
CoalingaCALIFORNIA12008

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