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

American Bittern Population Trend in California

All statesWetland birds

American Bittern in California has declined: down 34% on the route-weighted index since 1972.

-34%Since 1972TrendPercent 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 →
36Routes 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 →
53YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable American Bittern 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 →

No notable trend signals for American Bittern in California. See the full index history below.

American Bittern Population Forecast in California

If the recent trend holds, American Bittern in California is projected to rise about 159% by 2029 — from 0.05 in 2024 to a central estimate of 0.14 (95% range 0.00–0.40). A 5-year backtest shows a typical error of ±495.9%, with 100% of held-out values landing inside the 95% band.

+159%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 →
0.14Projected 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 →
0.00–0.4095% 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 →
±495.9%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, American Bittern in California is projected to rise about 159% by 2029 — from 0.05 in 2024 to a central estimate of 0.14 (95% range 0.00–0.40). A 5-year backtest shows a typical error of ±495.9%, with 100% 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 →
20250.150.000.41
20260.150.000.41
20270.140.000.41
20280.140.000.41
20290.140.000.40

American Bittern Survey Routes in California

Routes recording American Bittern 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 →
Glenn1320231971
Cordova319751975
Honey Lake320241972
Dorris320191975
Macdoel320171983
Nubieber220071990
Pennington220141971
Arvin219851985
Davis Creek219991993
Tranquillity220031972
Ora Loma219831972
Athlone219821982
Whiskeytown220052003
Gazelle120162016
Red Bluff120141972
Creston120022002
Shafter119861986
Collegeville119791968
Hughson119871982
Atwater120071976
Likely120241975
Crowley Lake119721972
Gold Hill119861986
Oilfields119681968
Gravesboro119851972

American Bittern Population Trend in Other States

alaskacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaslouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-dakotaohiooklahomaoregonpennsylvaniasouth-carolinasouth-dakotatexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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