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

Common Merganser Population Trend in Montana

All statesWaterfowl

Common Merganser in Montana has surged: up 313% on the route-weighted index since 1975.

+313%Since 1975TrendPercent 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 →
44Routes 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 Common Merganser Trends in MontanaNotable 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 Montana: up 313% on the route-weighted index since 1975.

Common Merganser Population Forecast in Montana

If the recent trend holds, Common Merganser in Montana is projected to stay roughly flat through 2029, near 0.25 (95% range 0.01–0.48). A 5-year backtest shows a typical error of ±46.5%, with 100% of held-out values landing inside the 95% band.

-9%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 →
0.25Projected 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 →
0.01–0.4895% 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 →
±46.5%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 Montana is projected to stay roughly flat through 2029, near 0.25 (95% range 0.01–0.48). A 5-year backtest shows a typical error of ±46.5%, with 100% 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 →
20250.240.010.47
20260.240.010.48
20270.240.010.48
20280.250.010.48
20290.250.010.48

Common Merganser Survey Routes in Montana

Routes recording Common Merganser in Montana.
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 →
Ninemile1120241993
Beaverhead819971981
Kalispell620071981
Fish Creek620192003
Libby Dam520241979
Great Falls419951973
Flatwillow419771977
Red Rock419891975
Augusta319971986
Swan Lake320232021
Maynard Coulee320222022
Willow Creek 2220071983
St Xavier 2220182018
Circle220001997
Two Dot220241976
Thompson Riv220211996
Wheat Basin220192019
Lima220191999
St Mary120001991
Logan Pass120121988
Glen120021992
St Regis120141978
Arlee120241981
Highwood120241990
Brusett119851985

Common Merganser Population Trend in Other States

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

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