BirdAnalyst
Species · Idaho · BBS 2025 Release · 1966–2024

Common Merganser Population Trend in Idaho

All statesWaterfowl

Common Merganser in Idaho has fallen sharply: down 67% on the route-weighted index since 1973.

-67%Since 1973TrendPercent 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 →
31Routes 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 →
46YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Common Merganser Trends in IdahoNotable 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 declinecomputed 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 fallen sharply in Idaho: down 67% on the route-weighted index since 1973.

Common Merganser Population Forecast in Idaho

If the recent trend holds, Common Merganser in Idaho is projected to fall about 85% by 2029 — from 0.20 in 2024 to a central estimate of 0.03 (95% range 0.00–2.2). A 5-year backtest shows a typical error of ±48.5%, with 100% of held-out values landing inside the 95% band.

-85%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 →
0.03Projected 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 →
0.00–2.295% 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 →
±48.5%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 Idaho is projected to fall about 85% by 2029 — from 0.20 in 2024 to a central estimate of 0.03 (95% range 0.00–2.2). A 5-year backtest shows a typical error of ±48.5%, with 100% 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 →
20250.110.002.3
20260.090.002.2
20270.070.002.2
20280.050.002.2
20290.030.002.2

Common Merganser Survey Routes in Idaho

Routes recording Common Merganser in Idaho.
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 →
Cascade10519841983
N Fork Cda R520191993
Cape Horn420181997
Rochat Divde420231996
Iron Springs420192019
Dougal Res420191990
Golden320081989
Centerville320191982
Gifford220171986
Nezperce220121968
Lolo Pass220031992
Triangle220241998
Magic Mtn220091998
Sawtooth City 2220242015
Salmon River220171988
Sunbeam220191994
Sawtooth Cty220102008
Naples120141973
Baker120051980
Leadore120232010
Springfield119761976
Coolin120241987
Marble Creek120121990
Pierce119971994
Burgdorf119981998

Common Merganser Population Trend in Other States

alaskaarizonacaliforniacoloradoconnecticutmainemarylandmassachusettsmichiganminnesotamontananevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-dakotaohiooregonpennsylvaniasouth-dakotautahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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