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Species · California · BBS 2026 Release · 1966–2025

MacGillivray's Warbler Population Trend in California

All statesForest birds

MacGillivray's Warbler in California has surged: up 241% on the route-weighted index since 1971.

+241%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 →
114Routes 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 MacGillivray'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 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 →

MacGillivray's Warbler has surged in California: up 241% on the route-weighted index since 1971.

MacGillivray's Warbler Population Forecast in California

If the recent trend holds, MacGillivray's Warbler in California is projected to rise about 65% by 2030 — from 1.1 in 2025 to a central estimate of 1.9 (95% range 1.0–2.7). A 5-year backtest shows a typical error of ±128.5%, with 20% of held-out values landing inside the 95% band.

+65%Change by 2030TrendPercent 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 →
1.9Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
1.0–2.795% 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 →
±128.5%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, MacGillivray's Warbler in California is projected to rise about 65% by 2030 — from 1.1 in 2025 to a central estimate of 1.9 (95% range 1.0–2.7). A 5-year backtest shows a typical error of ±128.5%, with 20% of held-out values landing inside the 95% band.19682030
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 →
20261.80.942.6
20271.80.962.6
20281.80.982.6
20291.81.002.7
20301.91.02.7

MacGillivray's Warbler Survey Routes in California

Routes recording MacGillivray'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 →
Mccloud2420211979
Pilot Creek1919961994
Cottage Spgs1719751968
Tuolumne Grove1620251972
Martins Fy1520091976
Riverton1420251973
Horse Creek1120191973
Johnsville1120251975
Lakeshore1120241972
Orleans1020121974
Dardanelle920191972
Woodfords920251974
Strawberry920191999
Downieville820251979
South Fork Mtn820222000
Greenhorn Mt620081971
Butte Meadow620141972
Junction Cty520121980
Lonesome Rdg520141994
Chester520171997
Little Truckee520251997
Pollock Pines520251997
Friday Ridge520251994
Carrville419701970
Westville420251971

MacGillivray's Warbler Population Trend in Other States

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Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.