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Species · Maine · BBS 2025 Release · 1966–2024

Mourning Warbler Population Trend in Maine

All statesForest birds

Mourning Warbler in Maine has fallen sharply: down 72% on the route-weighted index since 1974.

-72%Since 1974TrendPercent 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 →
54Routes 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 →
48YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Mourning Warbler 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 declinecomputed 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 →

Mourning Warbler has fallen sharply in Maine: down 72% on the route-weighted index since 1974.

Mourning Warbler Population Forecast in Maine

If the recent trend holds, Mourning Warbler in Maine is projected to rise about 428% by 2029 — from 0.05 in 2024 to a central estimate of 0.28 (95% range 0.00–0.99). A 5-year backtest shows a typical error of ±699%, with 100% of held-out values landing inside the 95% band.

+428%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 →
0.28Projected 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 →
0.00–0.9995% 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 →
±699%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, Mourning Warbler in Maine is projected to rise about 428% by 2029 — from 0.05 in 2024 to a central estimate of 0.28 (95% range 0.00–0.99). A 5-year backtest shows a typical error of ±699%, with 100% of held-out values landing inside the 95% band.19682029
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 →
20250.300.001.0
20260.300.001.0
20270.290.001.0
20280.290.000.99
20290.280.000.99

Mourning Warbler Survey Routes in Maine

Routes recording Mourning Warbler 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 →
Ashland720081980
Baxter519841979
Boundary520091996
Seboomook Lk420141984
Ft Fairfield420051993
Heron Lake320031983
Weeks Brook320111995
Priestly Br.320111994
Biddeford219761976
Nesowadnehun219981991
Deblois219841984
Northfield219761976
Greenville220061985
Baker Lake 2220112010
Waite219771977
Pillsbury Pd219681968
Washburn220051986
St David220051984
Big Twenty220081993
Northfield 2120222022
Andover120182016
Wilson Mills120241983
Bethel120142014
Reeds120002000
South Arm119951979

Mourning Warbler Population Trend in Other States

connecticutillinoisindianamarylandmassachusettsmichiganminnesotanew-hampshirenew-yorknorth-dakotaohiopennsylvaniavermontwest-virginiawisconsin

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