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

Northern Harrier Population Trend in Washington

All statesGeneralists

Northern Harrier in Washington has declined: down 32% on the route-weighted index since 1970.

-32%Since 1970TrendPercent 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 →
66Routes 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 →
56YearsYears 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 WashingtonNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

No notable trend signals for Northern Harrier in Washington. See the full index history below.

Northern Harrier Population Forecast in Washington

If the recent trend holds, Northern Harrier in Washington is projected to rise about 52% by 2029 — from 0.28 in 2024 to a central estimate of 0.43 (95% range 0.07–0.78). A 5-year backtest shows a typical error of ±127.4%, with 80% of held-out values landing inside the 95% band.

+52%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 →
0.43Projected 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 →
0.07–0.7895% 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 →
±127.4%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 Washington is projected to rise about 52% by 2029 — from 0.28 in 2024 to a central estimate of 0.43 (95% range 0.07–0.78). A 5-year backtest shows a typical error of ±127.4%, with 80% 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 →
20250.430.070.78
20260.430.070.78
20270.430.070.78
20280.430.070.78
20290.430.070.78

Northern Harrier Survey Routes in Washington

Routes recording Northern Harrier in Washington.
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 →
Walla Walla819931993
Pomona619991998
Wilbur520211985
Ewan420191985
Potholes420191996
Selah320122000
Arid Land Er319891988
Harrington320121973
Odessa320241993
Mesa320081994
Lake Chelan320222022
Moses Lake220211973
Mendota 2219941991
Wapato220211972
Asotin220241981
Bickleton220161984
Sulphur220191995
Nighthawk220242007
Curlew220122012
Richland220242006
Harwood219971993
Pomeroy220241998
Bay View220171999
Port Angeles120241984
Warm Beach120042004

Northern Harrier Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradodelawaregeorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-dakotatennesseetexasutahvermontvirginiawest-virginiawisconsinwyoming

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