BirdAnalyst
Species · BCR 32 · BBS 2026 Release · 1966–2025

Northern Harrier In Coastal California

All regionsCoastal CaliforniaBirds of prey

Northern Harrier in Coastal California has fallen sharply: down 71% on the route-weighted index since 1970.

-71%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 →
65Routes 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 →
57YearsYears 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 Coastal California: down 71% on the route-weighted index since 1970.

Northern Harrier In Coastal California Population Forecast

If the recent trend holds, Northern Harrier in Coastal California is projected to fall about 18% by 2030 — from 0.21 in 2025 to a central estimate of 0.17 (95% range 0.00–0.62). A 5-year backtest shows a typical error of ±50.1%, with 100% of held-out values landing inside the 95% band.

-18%Change by 2030TrendPercent 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 →
0.17Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.6295% 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 →
±50.1%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 Coastal California is projected to fall about 18% by 2030 — from 0.21 in 2025 to a central estimate of 0.17 (95% range 0.00–0.62). A 5-year backtest shows a typical error of ±50.1%, with 100% of held-out values landing inside the 95% band.19682030
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 →
20260.210.000.65
20270.200.000.65
20280.190.000.64
20290.180.000.63
20300.170.000.62

Routes In Coastal California

Routes recording Northern Harrier in Coastal California.
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 →
AtwaterCALIFORNIA72012
OilfieldsCALIFORNIA61999
AthloneCALIFORNIA62007
CollegevilleCALIFORNIA52004
MorenoCALIFORNIA41986
HollisterCALIFORNIA42007
AuburnCALIFORNIA31980
CohassetCALIFORNIA31999
OrlandCALIFORNIA32011
VentucopaCALIFORNIA31999
TranquillityCALIFORNIA32004
Hollister 2CALIFORNIA32021
RiovistaCALIFORNIA22025
Lockwood ValCALIFORNIA21987
GlennCALIFORNIA22018
JacksonCALIFORNIA21980
LockwoodCALIFORNIA22025
ZamoraCALIFORNIA22024
GreenfieldCALIFORNIA22025
Buena VistaCALIFORNIA21999
PescaderoCALIFORNIA22024
Red BluffCALIFORNIA11979
PenningtonCALIFORNIA12023
HughsonCALIFORNIA12013
CaruthersCALIFORNIA11987

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.