BirdAnalyst
Species · BCR 15 · BBS 2025 Release · 1966–2024

Brewer's Sparrow In Sierra Nevada

All regionsSierra NevadaGeneralists

Brewer's Sparrow in Sierra Nevada has fallen sharply: down 55% on the route-weighted index since 1971.

-55%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 →
14Routes 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 →
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 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 fallen sharply in Sierra Nevada: down 55% on the route-weighted index since 1971.

Brewer's Sparrow In Sierra Nevada Population Forecast

If the recent trend holds, Brewer's Sparrow in Sierra Nevada is projected to rise about 57% by 2029 — from 1.4 in 2024 to a central estimate of 2.2 (95% range 0.00–5.0). A 5-year backtest shows a typical error of ±129.6%, with 100% of held-out values landing inside the 95% band.

+57%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 →
2.2Projected 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 →
0.00–5.095% 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 →
±129.6%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, Brewer's Sparrow in Sierra Nevada is projected to rise about 57% by 2029 — from 1.4 in 2024 to a central estimate of 2.2 (95% range 0.00–5.0). A 5-year backtest shows a typical error of ±129.6%, 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 →
20252.20.005.0
20262.20.005.0
20272.20.005.0
20282.20.005.0
20292.20.005.0

Routes In Sierra Nevada

Routes recording Brewer's Sparrow in Sierra Nevada.
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 →
Eagle LakeCALIFORNIA112024
Last ChanceCALIFORNIA102019
SattleyCALIFORNIA82024
Little TruckeeCALIFORNIA62023
Silver CityCALIFORNIA51977
GoumazCALIFORNIA42011
CrestviewCALIFORNIA42024
DardanelleCALIFORNIA32017
Hat CreekCALIFORNIA21992
Pine MountainCALIFORNIA22009
ChilcootCALIFORNIA22024
WestvilleCALIFORNIA11977
JohnsvilleCALIFORNIA12024
WoodfordsCALIFORNIA12024

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