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

Wilson's Warbler Population Trend in California

All statesForest birds

Wilson's Warbler in California has fallen sharply: down 57% on the route-weighted index since 1970.

-57%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 →
168Routes 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 Wilson's Warbler 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 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 →

Wilson's Warbler has fallen sharply in California: down 57% on the route-weighted index since 1970.

Wilson's Warbler Population Forecast in California

If the recent trend holds, Wilson's Warbler in California is projected to rise about 50% by 2029 — from 1.4 in 2024 to a central estimate of 2.1 (95% range 1.0–3.1). A 5-year backtest shows a typical error of ±49.5%, with 80% of held-out values landing inside the 95% band.

+50%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 →
2.1Projected 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 →
1.0–3.195% 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 →
±49.5%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, Wilson's Warbler in California is projected to rise about 50% by 2029 — from 1.4 in 2024 to a central estimate of 2.1 (95% range 1.0–3.1). A 5-year backtest shows a typical error of ±49.5%, with 80% 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 →
20252.11.13.2
20262.11.13.2
20272.11.13.2
20282.11.03.2
20292.11.03.1

Wilson's Warbler Survey Routes in California

Routes recording Wilson's Warbler 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 →
Redwood N.P.4620101995
Point Reyes4420231970
Redwood N.P. 24320132012
Fish Rock2820141968
Pescadero2520241992
Navarro2120111972
Honeydew1720171968
Korbel1520241972
Ukiah1420111988
Crescent Cty1320241972
Laytonville1320241972
Holmes1120241968
Waterman Gap1120241972
Hiouchi1120142002
Genesee1020241972
Chester1020171997
Last Chance720191993
Morro Bay620131973
Carmel Val620241973
Greenhorn Mt619821974
Anza619811981
Hay Fork620172003
Dardanelle520191972
Anza Borrego519901985
Ship Mtn.520171994

Wilson's Warbler Population Trend in Other States

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