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

Northern Harrier Population Trend in Maine

All statesGeneralists

Northern Harrier in Maine has fallen sharply: down 56% on the route-weighted index since 1975.

-56%Since 1975TrendPercent 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 →
26Routes 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 →
36YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Northern Harrier 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 →

Northern Harrier has fallen sharply in Maine: down 56% on the route-weighted index since 1975.

Northern Harrier Population Forecast in Maine

If the recent trend holds, Northern Harrier in Maine is projected to fall about 74% by 2027 — from 0.10 in 2022 to a central estimate of 0.03 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±56%, with 100% of held-out values landing inside the 95% band.

-74%Change by 2027TrendPercent 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 →
0.03Projected 2027 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.1195% 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 →
±56%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, Northern Harrier in Maine is projected to fall about 74% by 2027 — from 0.10 in 2022 to a central estimate of 0.03 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±56%, with 100% of held-out values landing inside the 95% band.19662027
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 →
20230.030.000.12
20240.030.000.12
20250.030.000.11
20260.030.000.11
20270.030.000.11

Northern Harrier Survey Routes in Maine

Routes recording Northern Harrier 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 →
Hancock219871986
Ft Fairfield220041994
Westbrook119861986
South Arm119951995
Otisfield Gr119991995
Manchester119821981
Harmony120221991
Heron Lake119891989
Brooks120062006
Eastbrook120172017
Cooper119781975
Deblois120051966
Moose River120062006
Wytopitlock119831983
Forest Sta119831979
Ludlow119811978
Washburn119871983
Horse Mtn119951995
Ashland120041988
Boundary120151995
St David120051984
Lake Moxie120102010
Cornville120222022
Searsport120072007
Jefferson120082008

Northern Harrier Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradodelawaregeorgiaidahoillinoisindianaiowakansaskentuckylouisianamarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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