BirdAnalyst
Species · BCR 15 · BBS 2025 Release · 1966–2024

Common Merganser In Sierra Nevada

All regionsSierra NevadaWaterfowl

Common Merganser in Sierra Nevada has surged: up 84% on the route-weighted index since 1972.

+84%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 →
17Routes 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 →
43YearsYears 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 →

Common Merganser has surged in Sierra Nevada: up 84% on the route-weighted index since 1972.

Common Merganser In Sierra Nevada Population Forecast

If the recent trend holds, Common Merganser in Sierra Nevada is projected to fall about 72% by 2028 — from 0.82 in 2023 to a central estimate of 0.23 (95% range 0.00–0.53). A 5-year backtest shows a typical error of ±96.7%, with 40% of held-out values landing inside the 95% band.

-72%Change by 2028TrendPercent 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 →
0.23Projected 2028 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.5395% 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 →
±96.7%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 Sierra Nevada is projected to fall about 72% by 2028 — from 0.82 in 2023 to a central estimate of 0.23 (95% range 0.00–0.53). A 5-year backtest shows a typical error of ±96.7%, with 40% of held-out values landing inside the 95% band.19692028
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 →
20240.220.000.53
20250.230.000.53
20260.230.000.53
20270.230.000.53
20280.230.000.53

Routes In Sierra Nevada

Routes recording Common Merganser in Sierra Nevada.
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 →
GeneseeCALIFORNIA62023
RivertonCALIFORNIA42017
Eagle LakeCALIFORNIA32023
WoodfordsCALIFORNIA32022
ChilcootCALIFORNIA32023
Meadow ValleyCALIFORNIA22023
Little TruckeeCALIFORNIA22017
DardanelleCALIFORNIA12014
Bass LakeCALIFORNIA11981
JohnsvilleCALIFORNIA12021
Silver CityCALIFORNIA12013
Tuolumne GroveCALIFORNIA12016
SattleyCALIFORNIA12009
Butte MeadowCALIFORNIA12000
PaxtonCALIFORNIA12022
StrawberryCALIFORNIA12015
Last ChanceCALIFORNIA12009

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