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Species · California · BBS 2025 Release · 1966–2024

Black-crowned Night Heron Population Trend in California

All statesWetland birds

Black-crowned Night Heron in California has surged: up 152% on the route-weighted index since 1971.

+152%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 →
80Routes 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 →
55YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Black-crowned Night Heron 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 →

Black-crowned Night Heron has surged in California: up 151% on the route-weighted index since 1971.

Black-crowned Night Heron Population Forecast in California

If the recent trend holds, Black-crowned Night Heron in California is projected to rise about 127% by 2029 — from 0.16 in 2024 to a central estimate of 0.36 (95% range 0.00–1.0). A 5-year backtest shows a typical error of ±293%, with 100% of held-out values landing inside the 95% band.

+127%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 →
0.36Projected 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 →
0.00–1.095% 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 →
±293%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, Black-crowned Night Heron in California is projected to rise about 127% by 2029 — from 0.16 in 2024 to a central estimate of 0.36 (95% range 0.00–1.0). A 5-year backtest shows a typical error of ±293%, 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 →
20250.380.001.0
20260.380.001.0
20270.370.001.0
20280.370.001.0
20290.360.001.0

Black-crowned Night Heron Survey Routes in California

Routes recording Black-crowned Night Heron 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 →
Dorris3920191972
Ora Loma2819831972
Orland920141985
Crescent Cty620221975
Buena Vista620191990
Bakersfield520232003
Moreno520242017
Honey Lake520191973
Harbor Lake419911973
Foster Park319931993
Atwater320071973
Iron Gate320171988
Red Bluff219921969
Collegeville219751975
Palo Verde220131977
Orange Cove220042002
Cohasset219851985
Poway219801973
Sisquoc219941977
Cp. Pendleton219931978
Arvin220161984
Sattley220151976
Oroville220241979
Macdoel220181987
Moraga220042000

Black-crowned Night Heron Population Trend in Other States

alabamaarizonaarkansascoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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