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

Common Merganser Population Trend in Vermont

All statesWaterfowl

Common Merganser in Vermont has surged: up 202% on the route-weighted index since 1977.

+202%Since 1977TrendPercent 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 →
18Routes 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 →
36YearsYears 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 VermontNotable 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 Vermont: up 202% on the route-weighted index since 1977.

Common Merganser Population Forecast in Vermont

If the recent trend holds, Common Merganser in Vermont is projected to fall about 26% by 2029 — from 0.39 in 2024 to a central estimate of 0.29 (95% range 0.00–0.65). A 5-year backtest shows a typical error of ±108.8%, with 100% of held-out values landing inside the 95% band.

-26%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 →
0.29Projected 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 →
0.00–0.6595% 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 →
±108.8%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 Vermont is projected to fall about 26% by 2029 — from 0.39 in 2024 to a central estimate of 0.29 (95% range 0.00–0.65). A 5-year backtest shows a typical error of ±108.8%, with 100% of held-out values landing inside the 95% band.19662029
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 →
20250.280.000.64
20260.280.000.64
20270.280.000.64
20280.290.000.65
20290.290.000.65

Common Merganser Survey Routes in Vermont

Routes recording Common Merganser in Vermont.
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 →
Colchester520182013
Gaysville320181966
North Pownal220242021
Landgrove220242024
Shaftsbury220231986
Marlboro120162016
Stratton120241998
S Reading120241998
W Rutland120182004
St Johnsbury120122012
East Haven119951976
Middlesex120131990
East Calais120171993
Greensboro120241979
Fletcher120212010
Grand Isle120211977
Stowe120221995
Bristol120182018

Common Merganser Population Trend in Other States

alaskaarizonacaliforniacoloradoconnecticutidahomainemarylandmassachusettsmichiganminnesotamontananevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-dakotaohiooregonpennsylvaniasouth-dakotautahvirginiawashingtonwest-virginiawisconsinwyoming

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