BirdAnalyst
Species · California · BBS 2025 Release · 1966–2024

Fox Sparrow Population Trend in California

All statesGeneralists

Fox Sparrow in California has surged: up 233% on the route-weighted index since 1970.

+233%Since 1970TrendPercent 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 →
97Routes 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 Fox 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 →

Fox Sparrow has surged in California: up 233% on the route-weighted index since 1970.

Fox Sparrow Population Forecast in California

If the recent trend holds, Fox Sparrow in California is projected to rise about 67% by 2029 — from 1.9 in 2024 to a central estimate of 3.3 (95% range 1.7–4.8). A 5-year backtest shows a typical error of ±67.3%, with 60% of held-out values landing inside the 95% band.

+67%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 →
3.3Projected 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 →
1.7–4.895% 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 →
±67.3%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, Fox Sparrow in California is projected to rise about 67% by 2029 — from 1.9 in 2024 to a central estimate of 3.3 (95% range 1.7–4.8). A 5-year backtest shows a typical error of ±67.3%, with 60% of held-out values landing inside the 95% band.19682029
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 →
20253.21.64.7
20263.21.74.8
20273.21.74.8
20283.21.74.8
20293.31.74.8

Fox Sparrow Survey Routes in California

Routes recording Fox 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 →
Westville4820241971
Tahoe Nf4019941987
Greenhorn Mt3220081971
Johnsville2920241975
Genesee2920241976
South Fork Mtn2720222000
Pine Mountain2520171997
Cottage Spgs2019751968
Lakeshore2020241972
Pilot Creek1919961994
Valyermo1620191970
Tuolumne Grove1520241973
Bartle1420211972
Chester1320171999
Crowder Flat1220182006
Meadow Valley1220241999
Little Truckee1220231997
Dardanelle1120191973
Dirigio1020141999
Lassen Park819891972
Mt Pinos820041969
Hat Creek820181973
Gazelle819961996
Lumberyard720241976
Crowley Lake720171988

Fox Sparrow Population Trend in Other States

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