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

Common Merganser In Coastal California

All regionsCoastal CaliforniaWaterfowl

Common Merganser in Coastal California has declined: down 29% on the route-weighted index since 1978.

-29%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 →
22Routes 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 →
44YearsYears 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 →

No notable trend signals for Common Merganser in Coastal California. See the full index history below.

Common Merganser In Coastal California Population Forecast

If the recent trend holds, Common Merganser in Coastal California is projected to stay roughly flat through 2029, near 0.25 (95% range 0.02–0.47). A 5-year backtest shows a typical error of ±353.7%, with 40% of held-out values landing inside the 95% band.

n/aChange 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 →
0.25Projected 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 →
0.02–0.4795% 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 →
±353.7%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, Common Merganser in Coastal California is projected to stay roughly flat through 2029, near 0.25 (95% range 0.02–0.47). A 5-year backtest shows a typical error of ±353.7%, with 40% 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 →
20250.240.010.46
20260.240.010.47
20270.240.010.47
20280.240.020.47
20290.250.020.47

Routes In Coastal California

Routes recording Common Merganser 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 →
CopperopolisCALIFORNIA52021
OnoCALIFORNIA22012
AdelaidaCALIFORNIA21999
LockwoodCALIFORNIA22024
TomheadCALIFORNIA22005
Red BluffCALIFORNIA11978
RumseyCALIFORNIA11998
CoalingaCALIFORNIA12000
Orange CoveCALIFORNIA12004
Point ReyesCALIFORNIA12021
CohassetCALIFORNIA12019
OrlandCALIFORNIA11998
FairfaxCALIFORNIA12019
FolsomCALIFORNIA12023
Carmel ValCALIFORNIA12018
SangerCALIFORNIA12017
Gold HillCALIFORNIA12019
CoyoteCALIFORNIA12023
GreenfieldCALIFORNIA12021
TracyCALIFORNIA11993
PescaderoCALIFORNIA12012
Hough SpringsCALIFORNIA12002

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