BirdAnalyst
Species · BCR 32 · BBS 2025 Release · 1966–2024

Northern Harrier In Coastal California

All regionsCoastal CaliforniaGeneralists

Northern Harrier in Coastal California has fallen sharply: down 75% on the route-weighted index since 1970.

-75%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 →
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 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 75% on the route-weighted index since 1970.

Forecast

If the recent trend holds, Northern Harrier in Coastal California is projected to fall about 43% by 2029 — from 0.32 in 2024 to a central estimate of 0.18 (95% range 0.00–0.63). A 5-year backtest shows a typical error of ±111.7%, with 100% of held-out values landing inside the 95% band.

-43%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 →
0.18Projected 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 →
0.00–0.6395% 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 →
±111.7%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 43% by 2029 — from 0.32 in 2024 to a central estimate of 0.18 (95% range 0.00–0.63). A 5-year backtest shows a typical error of ±111.7%, 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 →
20250.220.000.67
20260.210.000.66
20270.200.000.65
20280.190.000.64
20290.180.000.63

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
RiovistaCALIFORNIA62024
OilfieldsCALIFORNIA61999
AthloneCALIFORNIA62007
CollegevilleCALIFORNIA52004
MorenoCALIFORNIA41986
HollisterCALIFORNIA42007
Ora LomaCALIFORNIA42024
AuburnCALIFORNIA31980
CohassetCALIFORNIA31999
OrlandCALIFORNIA32011
VentucopaCALIFORNIA31999
TranquillityCALIFORNIA32004
Hollister 2CALIFORNIA32021
Lockwood ValCALIFORNIA21987
Carrizo PlnCALIFORNIA22006
GlennCALIFORNIA22018
JacksonCALIFORNIA21980
ZamoraCALIFORNIA22024
Buena VistaCALIFORNIA21999
PescaderoCALIFORNIA22024
Red BluffCALIFORNIA11979
PenningtonCALIFORNIA12023
HughsonCALIFORNIA12013
CaruthersCALIFORNIA11987

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