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

Northern Harrier In BCR 4

All regionsBCR 4Generalists

Northern Harrier in BCR 4 has fallen sharply: down 66% on the route-weighted index since 1987.

-66%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 →
30Routes 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 →
34YearsYears 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 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 BCR 4: down 66% on the route-weighted index since 1987.

Northern Harrier In BCR 4 Population Forecast

If the recent trend holds, Northern Harrier in BCR 4 is projected to fall about 42% by 2029 — from 0.08 in 2024 to a central estimate of 0.05 (95% range 0.00–0.18). A 5-year backtest shows a typical error of ±88.8%, with 100% of held-out values landing inside the 95% band.

-42%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 →
0.05Projected 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 →
0.00–0.1895% 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 →
±88.8%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 BCR 4 is projected to fall about 42% by 2029 — from 0.08 in 2024 to a central estimate of 0.05 (95% range 0.00–0.18). A 5-year backtest shows a typical error of ±88.8%, with 100% 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 →
20250.060.000.19
20260.060.000.19
20270.050.000.18
20280.050.000.18
20290.050.000.18

Routes In BCR 4

Routes recording Northern Harrier 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 →
ChistochinaALASKA22023
CantwellALASKA21998
Lake LouiseALASKA22008
EagleALASKA12014
Chatanika RALASKA12007
LivengoodALASKA12011
SlanaALASKA12024
MaclarenALASKA12011
MonahanALASKA12021
ToklatALASKA12019
KalifonskyALASKA12016
Kenny LakeALASKA12000
SourdoughALASKA12013
SavageALASKA12024
Seven LakesALASKA11999
Burma RoadALASKA11998
Caribou Mtn.ALASKA12023
ColdfootALASKA12011
Donelly DomeALASKA12024
Unalakleet RiverALASKA11997
Hather CreekALASKA12016
Manley Ht SpALASKA12009
Moose CreekALASKA11997
Mt. FairplayALASKA11996
Murphy DomeALASKA12008

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