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

Swainson's Hawk Population Trend in California

All statesGeneralists

Swainson's Hawk in California has surged: up 24× on the route-weighted index since 1974.

24×Since 1974TrendPercent 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 →
51Routes 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 →
51YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Swainson's Hawk 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 →

Swainson's Hawk has surged in California: up 24× on the route-weighted index since 1974.

Swainson's Hawk Population Forecast in California

If the recent trend holds, Swainson's Hawk in California is projected to fall about 16% by 2029 — from 0.96 in 2024 to a central estimate of 0.80 (95% range 0.22–1.4). A 5-year backtest shows a typical error of ±59%, with 100% of held-out values landing inside the 95% band.

-16%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 →
0.80Projected 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 →
0.22–1.495% 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 →
±59%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, Swainson's Hawk in California is projected to fall about 16% by 2029 — from 0.96 in 2024 to a central estimate of 0.80 (95% range 0.22–1.4). A 5-year backtest shows a typical error of ±59%, with 100% of held-out values landing inside the 95% band.19722029
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 →
20250.740.151.3
20260.750.171.3
20270.770.181.4
20280.790.201.4
20290.800.221.4

Swainson's Hawk Survey Routes in California

Routes recording Swainson's Hawk 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 →
Collegeville 24220232007
Ora Loma2920241981
Athlone2420071972
Atwater1420121974
Westley1320241974
Zamora1020241977
Staten Is.920241994
Buena Vista820192017
Tracy 2620242010
Cedarville520241990
Likely420241976
Sattley420242024
Nubieber220072007
Collegeville220041980
Hughson220241994
Dorris220191992
Tranquillity220241981
Parker Dam219751975
Tracy220092002
Glamis219741974
Iron Gate120062006
Carrizo Pln120222009
Pennington120231972
Riovista120222005
Glenn120091999

Swainson's Hawk Population Trend in Other States

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