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

Brown-headed Cowbird In Coastal California

All regionsCoastal CaliforniaGeneralists

Brown-headed Cowbird in Coastal California has risen sharply: up 61% on the route-weighted index since 1970.

+61%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 →
116Routes 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 increasecomputed 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 →

Brown-headed Cowbird has risen sharply in Coastal California: up 61% on the route-weighted index since 1970.

Brown-headed Cowbird In Coastal California Population Forecast

If the recent trend holds, Brown-headed Cowbird in Coastal California is projected to rise about 73% by 2030 — from 4.9 in 2025 to a central estimate of 8.5 (95% range 3.2–14). A 5-year backtest shows a typical error of ±94.9%, with 80% of held-out values landing inside the 95% band.

+73%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 →
8.5Projected 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 →
3.2–1495% 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 →
±94.9%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, Brown-headed Cowbird in Coastal California is projected to rise about 73% by 2030 — from 4.9 in 2025 to a central estimate of 8.5 (95% range 3.2–14). A 5-year backtest shows a typical error of ±94.9%, with 80% 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 →
20268.53.114
20278.53.114
20288.53.114
20298.53.114
20308.53.214

Routes In Coastal California

Routes recording Brown-headed Cowbird 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 →
TiptonCALIFORNIA491997
AtwaterCALIFORNIA332012
CaruthersCALIFORNIA311987
JacksonCALIFORNIA301992
CordovaCALIFORNIA281980
Staten Is.CALIFORNIA272025
CollegevilleCALIFORNIA202004
HollisterCALIFORNIA202011
Big BearCALIFORNIA191986
CoyoteCALIFORNIA192025
Yokohl ValCALIFORNIA181997
Collegeville 2CALIFORNIA182023
White RiverCALIFORNIA171992
TracyCALIFORNIA172009
Ora LomaCALIFORNIA162025
AthloneCALIFORNIA162007
CopperopolisCALIFORNIA152024
BakersfieldCALIFORNIA142023
CohassetCALIFORNIA142025
VentucopaCALIFORNIA141998
FolsomCALIFORNIA112025
OilfieldsCALIFORNIA102005
Orange CoveCALIFORNIA102016
PowayCALIFORNIA101980
Gold HillCALIFORNIA102025

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