BirdAnalyst
Species · California · BBS 2026 Release · 1966–2025

Brewer's Sparrow Population Trend in California

All statesArid-land birds

Brewer's Sparrow in California has surged: up 163% on the route-weighted index since 1971.

+163%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 →
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 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 163% 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 2030, near 2.9 (95% range 1.6–4.2). A 5-year backtest shows a typical error of ±21.5%, with 100% of held-out values landing inside the 95% band.

-5%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 →
2.9Projected 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 →
1.6–4.295% 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 →
±21.5%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 2030, near 2.9 (95% range 1.6–4.2). A 5-year backtest shows a typical error of ±21.5%, with 100% of held-out values landing inside the 95% band.19692030
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 →
20262.91.54.2
20272.91.54.2
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20302.91.64.2

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 →
Ravendale6620251973
Bodie6120251982
Crowley Lake5420251972
Bridgeport2819771972
Clear Lk Res2420181972
Honey Lake2320251972
Benton1620251973
Sattley1420251972
Ingalls1220011973
Willow Spgs1119771976
Last Chance1020191993
Deep Springs920221972
Ventucopa820011995
Macdoel720191972
Eureka Val720161975
Big Bear719861969
Joshua Tree619911972
Madeline620251997
Tecopa619871979
Kelso Valley520251973
Fall River Mills520112006
Onyx519981970
Silver City519771977
Goumaz420111997
Calif City419781978

Brewer's Sparrow Population Trend in Other States

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