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Species · California · BBS 2026 Release · 1966–2025

Violet-green Swallow Population Trend in California

All statesAerial insectivores

Violet-green Swallow in California has fallen sharply: down 63% on the route-weighted index since 1970.

-63%Since 1970TrendPercent 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 →
184Routes 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 →
57YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Violet-green Swallow 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 declinecomputed 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 →

Violet-green Swallow has fallen sharply in California: down 63% on the route-weighted index since 1970.

Violet-green Swallow Population Forecast in California

If the recent trend holds, Violet-green Swallow in California is projected to fall about 60% by 2030 — from 3.9 in 2025 to a central estimate of 1.6 (95% range 0.00–4.0). A 5-year backtest shows a typical error of ±45.2%, with 100% of held-out values landing inside the 95% band.

-60%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 →
1.6Projected 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 →
0.00–4.095% 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 →
±45.2%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, Violet-green Swallow in California is projected to fall about 60% by 2030 — from 3.9 in 2025 to a central estimate of 1.6 (95% range 0.00–4.0). A 5-year backtest shows a typical error of ±45.2%, with 100% 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 →
20262.10.004.5
20271.90.004.4
20281.80.004.3
20291.70.004.1
20301.60.004.0

Violet-green Swallow Survey Routes in California

Routes recording Violet-green Swallow 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 →
Arvin17219881982
Big Bear8219861969
Lake Hemet6319861970
Riovista5720221992
Fairfax4720241972
Valyermo4120191970
Carmel Val4020251973
Lockwood4020251972
Tres Pinos 23920112005
Fallsvale3319811970
Coyote2720251972
White River2419921972
Point Reyes2220251970
Glenn2219911985
Glen Ellen2220041972
Greenfield2020251973
Fish Rock1820141968
Ingalls1719731973
Mesa Grande1720251970
Adelaida1720251970
Imperial Dam1619861978
Gold Hill1620251978
Cal Hot Spgs1620191993
Santa Ynez1520191969
Moraga1320251972

Violet-green Swallow Population Trend in Other States

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