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 1970
245Routes In State
56Years

Notable Brown-headed Cowbird Trends in California

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 2029
7.3Projected 2029 index
3.7–1195% range
±93.2%Backtest error
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 index95% low95% high
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.
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.