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Species · BCR 4 · BBS 2025 Release · 1966–2024

Common Merganser In BCR 4

All regionsBCR 4Waterfowl

Common Merganser in BCR 4 has surged: up 320% on the route-weighted index since 1987.

+320%Since 1987TrendPercent 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 →
19Routes In RegionSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
29YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable SignalsNotable 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 BCR 4: up 320% on the route-weighted index since 1987.

Common Merganser In BCR 4 Population Forecast

If the recent trend holds, Common Merganser in BCR 4 is projected to fall about 11% by 2029 — from 0.39 in 2024 to a central estimate of 0.35 (95% range 0.09–0.61). A 5-year backtest shows a typical error of ±51.1%, with 80% of held-out values landing inside the 95% band.

-11%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 →
0.35Projected 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 →
0.09–0.6195% 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 →
±51.1%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 BCR 4 is projected to fall about 11% by 2029 — from 0.39 in 2024 to a central estimate of 0.35 (95% range 0.09–0.61). A 5-year backtest shows a typical error of ±51.1%, with 80% of held-out values landing inside the 95% band.19822029
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 →
20250.330.060.59
20260.330.070.59
20270.340.070.60
20280.340.080.60
20290.350.090.61

Routes In BCR 4

Routes recording Common Merganser in BCR 4.
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 →
Anvik RiverALASKA82024
Burma RoadALASKA42009
Unalakleet RiverALASKA32024
Ft. RichrdsnALASKA32000
CircleALASKA22022
Chatanika RALASKA22023
ChistochinaALASKA22008
MonahanALASKA22010
Anchor RiverALASKA22023
PetersvilleALASKA22003
Seven LakesALASKA22022
Kanuti CanynALASKA22024
KalifonskyALASKA11982
Kenny LakeALASKA11998
Hatcher PassALASKA12009
Chena Hot Spring 2ALASKA12024
Hather CreekALASKA12011
TatalinaALASKA12009
Paxson LakeALASKA11992

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