BirdAnalyst
Species · New Hampshire · BBS 2025 Release · 1966–2024

Common Merganser Population Trend in New Hampshire

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Common Merganser in New Hampshire has surged: up 130% on the route-weighted index since 1976.

+130%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 →
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 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 130% 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 stay roughly flat through 2029, near 0.27 (95% range 0.07–0.47). A 5-year backtest shows a typical error of ±50.5%, with 80% of held-out values landing inside the 95% band.

-3%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 →
0.27Projected 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 →
0.07–0.4795% 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 →
±50.5%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 New Hampshire is projected to stay roughly flat through 2029, near 0.27 (95% range 0.07–0.47). A 5-year backtest shows a typical error of ±50.5%, with 80% of held-out values landing inside the 95% band.19702029
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 →
20250.250.050.45
20260.250.050.45
20270.260.060.46
20280.260.060.46
20290.270.070.47

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 →
Walpole420241996
Marlow320212012
Glen320212005
Jefferson Hl220221988
Stratford220191978
Fitzwilliam120232007
Mt Chocorua120241978
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 2026-05-22.