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

Black-chinned Sparrow In Coastal California

All regionsCoastal CaliforniaGeneralists

Black-chinned Sparrow in Coastal California has collapsed: down 78% on the route-weighted index since 1971.

-78%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 →
44Routes 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 →

Black-chinned Sparrow has collapsed in Coastal California: down 78% on the route-weighted index since 1971.

Forecast

If the recent trend holds, Black-chinned Sparrow in Coastal California is projected to fall about 60% by 2029 — from 1.8 in 2024 to a central estimate of 0.72 (95% range 0.00–3.6). A 5-year backtest shows a typical error of ±59.2%, with 100% of held-out values landing inside the 95% band.

-60%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 →
0.72Projected 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 →
0.00–3.695% 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 →
±59.2%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, Black-chinned Sparrow in Coastal California is projected to fall about 60% by 2029 — from 1.8 in 2024 to a central estimate of 0.72 (95% range 0.00–3.6). A 5-year backtest shows a typical error of ±59.2%, 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 →
20250.880.003.8
20260.840.003.8
20270.800.003.7
20280.760.003.7
20290.720.003.6

Routes In Coastal California

Routes recording Black-chinned 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 →
Cuyamaca PkCALIFORNIA262024
Elsinore MtnCALIFORNIA162024
Anza 2CALIFORNIA162024
WoodlandsCALIFORNIA152024
Big BearCALIFORNIA141986
Lake Hemet 2CALIFORNIA142023
Cleveland NfCALIFORNIA142018
Lake CachumaCALIFORNIA122014
Green ValleyCALIFORNIA112023
Cleveland Nf 2CALIFORNIA92022
Oak GroveCALIFORNIA72024
AlamarCALIFORNIA62017
Lake HemetCALIFORNIA51977
Sawmill MtnCALIFORNIA42022
FallsvaleCALIFORNIA41981
JacumbaCALIFORNIA42024
JofeganCALIFORNIA42009
Mt PinosCALIFORNIA32004
StonyfordCALIFORNIA32016
San Benito Mtn.CALIFORNIA32009
Yokohl ValCALIFORNIA21978
Foster ParkCALIFORNIA21981
San YsidroCALIFORNIA21976
FairfaxCALIFORNIA21987
TujungaCALIFORNIA22012

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