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

Brewer's Sparrow Population Trend in California

All statesGeneralists

Brewer's Sparrow in California has surged: up 138% on the route-weighted index since 1971.

+138%Since 1971TrendPercent 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 →
64Routes 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 →
55YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Brewer's Sparrow 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 →

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 →

Brewer's Sparrow has surged in California: up 138% on the route-weighted index since 1971.

Brewer's Sparrow Population Forecast in California

If the recent trend holds, Brewer's Sparrow in California is projected to stay roughly flat through 2029, near 2.9 (95% range 1.5–4.2). A 5-year backtest shows a typical error of ±22.1%, with 100% of held-out values landing inside the 95% band.

-6%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 →
2.9Projected 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 →
1.5–4.295% 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 →
±22.1%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, Brewer's Sparrow in California is projected to stay roughly flat through 2029, near 2.9 (95% range 1.5–4.2). A 5-year backtest shows a typical error of ±22.1%, with 100% of held-out values landing inside the 95% band.19692029
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 →
20252.81.54.2
20262.91.54.2
20272.91.54.2
20282.91.54.2
20292.91.54.2

Brewer's Sparrow Survey Routes in California

Routes recording Brewer's Sparrow 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 →
Bodie7020241982
Crowley Lake6620241972
Ravendale5220241973
Benton3020241973
Honey Lake2820241972
Bridgeport2819771972
Clear Lk Res2420181972
Ingalls1220011973
Eagle Lake1120241969
Willow Spgs1119771976
Last Chance1020191993
Deep Springs920221972
Ventucopa820011995
Sattley820241972
Macdoel720191972
Eureka Val720161975
Big Bear719861969
Joshua Tree619911972
Little Truckee620231997
Tecopa619871979
Fall River Mills520112006
Onyx519981970
Silver City519771977
Madeline420241997
Goumaz420111997

Brewer's Sparrow Population Trend in Other States

arizonacoloradoidahokansasmontananebraskanevadanew-mexiconorth-dakotaoklahomaoregonsouth-dakotatexasutahwashingtonwyoming

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