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

Brown-headed Cowbird Population Trend in California

All statesGeneralists

Brown-headed Cowbird in California has increased: up 35% on the route-weighted index since 1970.

+35%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 →
245Routes 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 Brown-headed Cowbird Trends in CaliforniaNotable 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 Brown-headed Cowbird in California. See the full index history below.

Brown-headed Cowbird Population Forecast in California

If the recent trend holds, Brown-headed Cowbird in California is projected to rise about 42% by 2029 — from 5.1 in 2024 to a central estimate of 7.3 (95% range 3.7–11). A 5-year backtest shows a typical error of ±93.2%, with 20% 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 →
7.3Projected 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 →
3.7–1195% 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 →
±93.2%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 California is projected to rise about 42% by 2029 — from 5.1 in 2024 to a central estimate of 7.3 (95% range 3.7–11). A 5-year backtest shows a typical error of ±93.2%, with 20% 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 →
20257.23.611
20267.23.711
20277.23.711
20287.23.711
20297.33.711

Brown-headed Cowbird Survey Routes in California

Routes recording Brown-headed Cowbird in 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 →
Dorris20020191972
Tipton4919971972
Atwater3320121973
Caruthers3119871972
Jackson3019921972
Cedarville3020241974
Cordova2819801974
Staten Is.2820241994
Iron Gate2820191988
Trona2719771977
Ora Loma2720241973
Ingalls2520011973
Red Bluff2320241968
Palo Verde2220241973
Chilcoot2220241998
Glenn2120231975
Crowder Flat2120192002
Horse Creek2020191971
Collegeville2020041973
Hollister2020111974
Coyote2020241973
Big Bear1919861969
Sattley1920241973
Yokohl Val1819971973
Collegeville 21820232007

Brown-headed Cowbird Population Trend in Other States

alabamaalaskaarizonaarkansascoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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