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

Northern Harrier Population Trend in Idaho

All statesGeneralists

Northern Harrier in Idaho has declined: down 43% on the route-weighted index since 1970.

-43%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 →
47Routes 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 IdahoNotable 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 Idaho. See the full index history below.

Northern Harrier Population Forecast in Idaho

If the recent trend holds, Northern Harrier in Idaho is projected to fall about 36% by 2029 — from 1.1 in 2024 to a central estimate of 0.69 (95% range 0.00–1.5). A 5-year backtest shows a typical error of ±24%, with 100% of held-out values landing inside the 95% band.

-36%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 →
0.69Projected 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 →
0.00–1.595% 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 →
±24%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 Idaho is projected to fall about 36% by 2029 — from 1.1 in 2024 to a central estimate of 0.69 (95% range 0.00–1.5). A 5-year backtest shows a typical error of ±24%, 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 →
20250.710.001.5
20260.700.001.5
20270.700.001.5
20280.690.001.5
20290.690.001.5

Northern Harrier Survey Routes in Idaho

Routes recording Northern Harrier in Idaho.
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 →
Dubois520241968
Leadore420241979
Glenns Ferry419861969
Crane Creek420161988
Naples320241977
Twin Buttes320231990
Acequia320121979
Tractor Flat320241985
Picabo320211988
Cabarton319941994
Mora320222019
Sawtooth Cty320141988
Pasadena Val320161987
Baker220241978
Centerville219821982
Craters220181980
Springfield220181969
Pocatello220181980
Joel220051989
Iron Springs220241988
Silver City220131989
Mud Lake220221988
Cedar Hill220241990
Almo220231989
Daniels Res220181988

Northern Harrier Population Trend in Other States

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

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