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Species · California · BBS 2025 Release · 1966–2024

Hermit Warbler Population Trend in California

All statesForest birds

Hermit Warbler in California has surged: up 446% on the route-weighted index since 1970.

+446%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 →
109Routes 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 Hermit 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 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 →

Hermit Warbler has surged in California: up 446% on the route-weighted index since 1970.

Hermit Warbler Population Forecast in California

If the recent trend holds, Hermit Warbler in California is projected to rise about 70% by 2029 — from 2.7 in 2024 to a central estimate of 4.5 (95% range 2.6–6.5). A 5-year backtest shows a typical error of ±63.8%, with 40% of held-out values landing inside the 95% band.

+70%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 →
4.5Projected 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 →
2.6–6.595% 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 →
±63.8%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, Hermit Warbler in California is projected to rise about 70% by 2029 — from 2.7 in 2024 to a central estimate of 4.5 (95% range 2.6–6.5). A 5-year backtest shows a typical error of ±63.8%, with 40% 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 →
20254.32.46.2
20264.42.56.3
20274.42.56.3
20284.52.66.4
20294.52.66.5

Hermit Warbler Survey Routes in California

Routes recording Hermit 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 →
Johnsville6020241975
Lumberyard4820241976
Martins Fy4620091976
Pilot Creek4619961994
Butte Meadow4220141972
Friday Ridge3920241994
Lonesome Rdg3420141994
South Fork Mtn2920222000
Redwood N.P. 22720132012
Riverton2020231974
Placerville1820241998
Downieville1720241976
Hiouchi1420142002
Meadow Valley1120241999
Laytonville1020241974
Westville920241971
Navarro920071976
Alderpoint920121974
Genesee920241973
Carrville819701970
Ship Mtn.820171994
Holmes720241968
Burnt Ranch720161998
Chester720171997
Forest Hill620221997

Hermit Warbler Population Trend in Other States

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