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

Violet-green Swallow Population Trend in California

All statesAerial insectivores

Violet-green Swallow in California has fallen sharply: down 62% on the route-weighted index since 1970.

-62%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 →
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 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 62% 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 49% by 2029 — from 3.0 in 2024 to a central estimate of 1.5 (95% range 0.00–4.0). A 5-year backtest shows a typical error of ±44.1%, with 100% of held-out values landing inside the 95% band.

-49%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 →
1.5Projected 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 →
0.00–4.095% 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 →
±44.1%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 49% by 2029 — from 3.0 in 2024 to a central estimate of 1.5 (95% range 0.00–4.0). A 5-year backtest shows a typical error of ±44.1%, 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 →
20252.00.004.5
20261.90.004.3
20271.80.004.2
20281.70.004.1
20291.50.004.0

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
Carmel Val4120241973
Valyermo4120191970
Tres Pinos 23920112005
Fallsvale3319811970
White River2419921972
Point Reyes2320231970
Glenn2219911985
Glen Ellen2220041972
Lockwood2020241972
Fish Rock1820141968
Adelaida1820241970
Ingalls1719731973
Folsom1720241984
Imperial Dam1619861978
Cal Hot Spgs1620191993
Santa Ynez1520191969
Coyote1320241972
Forest Hill 21120052005
Auburn1119801969
Likely1120191973

Violet-green Swallow Population Trend in Other States

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