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Species · California · BBS 2026 Release · 1966–2025

Blue Grosbeak Population Trend in California

All statesForest birds

Blue Grosbeak in California has risen sharply: up 50% on the route-weighted index since 1971.

+50%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 →
71Routes 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 Blue Grosbeak 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 →

Blue Grosbeak has risen sharply in California: up 50% on the route-weighted index since 1971.

Blue Grosbeak Population Forecast in California

If the recent trend holds, Blue Grosbeak in California is projected to fall about 17% by 2030 — from 0.47 in 2025 to a central estimate of 0.39 (95% range 0.08–0.70). A 5-year backtest shows a typical error of ±90.5%, with 100% of held-out values landing inside the 95% band.

-17%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 →
0.39Projected 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 →
0.08–0.7095% 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 →
±90.5%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, Blue Grosbeak in California is projected to fall about 17% by 2030 — from 0.47 in 2025 to a central estimate of 0.39 (95% range 0.08–0.70). A 5-year backtest shows a typical error of ±90.5%, with 100% of held-out values landing inside the 95% band.19692030
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 →
20260.380.070.69
20270.380.070.69
20280.380.070.69
20290.390.080.69
20300.390.080.70

Blue Grosbeak Survey Routes in California

Routes recording Blue Grosbeak 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 →
Cp. Pendleton2920041970
Atwater1020121989
Jofegan 2820252024
Staten Is.820251994
Tres Pinos 2720112005
Anza720041971
Mesa Grande620251986
Moreno520251985
Onyx420011969
Athlone420072003
Orland420151988
Bakersfield320031969
Higgins Corn320182018
Greenfield320251976
Havasu Lake319731973
Anza 2320252005
Buena Vista319941993
Kelso Valley220242024
Pennington220191971
Calif City219801979
Glamis219771977
San Ysidro220131976
Zamora220251983
Copperopolis220242024
Oneals220112009

Blue Grosbeak Population Trend in Other States

alabamaarizonaarkansascoloradodelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamarylandminnesotamississippimissourimontananebraskanevadanew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniasouth-carolinasouth-dakotatennesseetexasutahvirginiawest-virginiawyoming

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