BirdAnalyst
Species · BCR 32 · BBS 2025 Release · 1966–2024

Brewer's Sparrow In Coastal California

All regionsCoastal CaliforniaGeneralists

Brewer's Sparrow in Coastal California has collapsed: down 94% on the route-weighted index since 1971.

-94%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 →
10Routes In RegionSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
40YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable SignalsNotable 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 declinecomputed 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 collapsed in Coastal California: down 94% on the route-weighted index since 1971.

Brewer's Sparrow In Coastal California Population Forecast

If the recent trend holds, Brewer's Sparrow in Coastal California is projected to fall about 100% by 2024 — from 0.06 in 2019 to a central estimate of 0.00 (95% range 0.00–0.49). A 5-year backtest shows a typical error of ±66.3%, with 100% of held-out values landing inside the 95% band.

-100%Change by 2024TrendPercent 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 →
0.00Projected 2024 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.4995% 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 →
±66.3%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 Coastal California is projected to fall about 100% by 2024 — from 0.06 in 2019 to a central estimate of 0.00 (95% range 0.00–0.49). A 5-year backtest shows a typical error of ±66.3%, with 100% of held-out values landing inside the 95% band.19692024
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 →
20200.040.000.54
20210.030.000.52
20220.020.000.51
20230.010.000.50
20240.000.000.49

Routes In Coastal California

Routes recording Brewer's Sparrow in Coastal 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 →
VentucopaCALIFORNIA82001
Big BearCALIFORNIA71986
Lockwood ValCALIFORNIA32019
Lake HemetCALIFORNIA21974
Cp. PendletonCALIFORNIA21980
Mt PinosCALIFORNIA11984
Lake SuccessCALIFORNIA11972
Mesa GrandeCALIFORNIA11975
ValyermoCALIFORNIA11996
Green ValleyCALIFORNIA11997

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