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

Common Merganser Population Trend in Maine

All statesWaterfowl

Common Merganser in Maine has risen sharply: up 67% on the route-weighted index since 1976.

+67%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 →
42Routes 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 MaineNotable 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 risen sharply in Maine: up 67% on the route-weighted index since 1976.

Common Merganser Population Forecast in Maine

If the recent trend holds, Common Merganser in Maine is projected to fall about 33% by 2029 — from 0.21 in 2024 to a central estimate of 0.14 (95% range 0.00–0.36). A 5-year backtest shows a typical error of ±65.6%, with 100% of held-out values landing inside the 95% band.

-33%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 →
0.14Projected 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 →
0.00–0.3695% 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 →
±65.6%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 Maine is projected to fall about 33% by 2029 — from 0.21 in 2024 to a central estimate of 0.14 (95% range 0.00–0.36). A 5-year backtest shows a typical error of ±65.6%, 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 →
20250.140.000.36
20260.140.000.36
20270.140.000.36
20280.140.000.36
20290.140.000.36

Common Merganser Survey Routes in Maine

Routes recording Common Merganser in Maine.
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 →
Hudson519951995
Greenwood420141992
Harmony420161992
Castine419861986
Baxter419841982
Bowdoin Ctr320021990
Winn320221996
Ft Fairfield319941994
Wilson Mills220241984
South Arm219941984
Northfield219791979
Moose River220051997
Carrabassett220241984
Seboomook Lk220141991
Greenville219971976
Horse Mtn220101983
Bethel120081979
Nesowadnehun120171991
Reeds120211999
Otisfield Gr119921992
Hartford120132013
East Troy120061992
Topsfield119921992
Heron Lake119961996
Eastbrook119941994

Common Merganser Population Trend in Other States

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

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