BirdAnalyst
Species · New Hampshire · BBS 2026 Release · 1966–2025

Common Merganser Population Trend in New Hampshire

All statesWaterfowl

Common Merganser in New Hampshire has surged: up 107% on the route-weighted index since 1976.

+107%Since 1976TrendPercent 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 →
12Routes 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 →
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 Common Merganser Trends in New HampshireNotable 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 New Hampshire: up 107% on the route-weighted index since 1976.

Common Merganser Population Forecast in New Hampshire

If the recent trend holds, Common Merganser in New Hampshire is projected to rise about 190% by 2030 — from 0.09 in 2025 to a central estimate of 0.25 (95% range 0.05–0.46). A 5-year backtest shows a typical error of ±83.1%, with 100% of held-out values landing inside the 95% band.

+190%Change by 2030TrendPercent 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 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.05–0.4695% 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 →
±83.1%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 New Hampshire is projected to rise about 190% by 2030 — from 0.09 in 2025 to a central estimate of 0.25 (95% range 0.05–0.46). A 5-year backtest shows a typical error of ±83.1%, with 100% of held-out values landing inside the 95% band.19702030
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 →
20260.240.040.44
20270.240.040.45
20280.250.040.45
20290.250.050.45
20300.250.050.46

Common Merganser Survey Routes in New Hampshire

Routes recording Common Merganser in New Hampshire.
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 →
Marlow320212012
Glen320212005
Jefferson Hl220221988
Stratford220191978
Fitzwilliam120252007
Mt Chocorua120241978
Walpole120251996
Lempster120241994
Franconia120191970
Milan120191972
Dixvil Notch120141998
Clarksville120141976

Common Merganser Population Trend in Other States

alaskaarizonacaliforniacoloradoconnecticutidahomainemarylandmassachusettsmichiganminnesotamontananevadanew-jerseynew-mexiconew-yorknorth-dakotaohiooregonpennsylvaniasouth-dakotautahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.