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

Western Tanager Population Trend in California

All statesGeneralists

Western Tanager in California has risen sharply: up 74% on the route-weighted index since 1970.

+74%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 →
197Routes 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 Western Tanager 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 →

Western Tanager has risen sharply in California: up 74% on the route-weighted index since 1970.

Western Tanager Population Forecast in California

If the recent trend holds, Western Tanager in California is projected to rise about 45% by 2029 — from 8.2 in 2024 to a central estimate of 12 (95% range 7.6–16). A 5-year backtest shows a typical error of ±68.3%, with 0% of held-out values landing inside the 95% band.

+45%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 →
12Projected 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 →
7.6–1695% 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 →
±68.3%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, Western Tanager in California is projected to rise about 45% by 2029 — from 8.2 in 2024 to a central estimate of 12 (95% range 7.6–16). A 5-year backtest shows a typical error of ±68.3%, with 0% 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 →
2025117.216
2026127.316
2027127.416
2028127.516
2029127.616

Western Tanager Survey Routes in California

Routes recording Western Tanager 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 →
Eagle Lake6320241969
Hay Fork6020172001
Horse Creek5820191970
Johnsville5720241975
Lumberyard5620241976
Placerville5420241997
Bartle4820211972
Cecilville4720171999
Orleans4620121972
South Fork Mtn4520222000
Orleans 24220142014
Alderpoint4120121974
Pollock Pines4020241997
Hough Springs3820071999
Pine Mountain3720171997
Lakeshore3520241972
Hullville3220191968
Greenhorn Mt3220081971
Butte Meadow3220141972
Crestview3220241997
Stonyford3120182015
Westville3020241971
Goumaz3020111997
Friday Ridge3020241994
Silver City2920131972

Western Tanager Population Trend in Other States

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