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Species · California · BBS 2025 Release · 1966–2024

Bell's Sparrow Population Trend in California

All statesGeneralists

Bell's Sparrow in California has edged down: down 21% on the route-weighted index since 1971.

-21%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 →
70Routes 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 Bell'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 →

No notable trend signals for Bell's Sparrow in California. See the full index history below.

Bell's Sparrow Population Forecast in California

If the recent trend holds, Bell's Sparrow in California is projected to rise about 30% by 2029 — from 0.52 in 2024 to a central estimate of 0.67 (95% range 0.13–1.2). A 5-year backtest shows a typical error of ±59.6%, with 100% of held-out values landing inside the 95% band.

+30%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 →
0.67Projected 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 →
0.13–1.295% 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 →
±59.6%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, Bell's Sparrow in California is projected to rise about 30% by 2029 — from 0.52 in 2024 to a central estimate of 0.67 (95% range 0.13–1.2). A 5-year backtest shows a typical error of ±59.6%, 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 →
20250.670.131.2
20260.670.131.2
20270.670.131.2
20280.670.131.2
20290.670.131.2

Bell's Sparrow Survey Routes in California

Routes recording Bell'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 →
Willow Springs 21620242015
Calif City1220151977
Stonyford1120182015
Goldstone1020091969
Lockwood Val1020191970
Rumsey820081980
French Gulch820062004
Hough Springs820071999
Cuyamaca Pk720241973
Tujunga620121975
Onyx520151974
Oak Grove520241969
Bartlett Sps420181974
Greenfield420242014
Woodlands420212016
Ventucopa320011972
Carrizo Pln320231970
San Benito Mtn.320092003
Shafter319851971
Barstow319981972
Lucerne Val320241974
Poway319801975
Ft Irwin319811978
Maricopa320241970
Kelso Valley220241975

Bell's Sparrow Population Trend in Other States

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