BirdAnalyst
Species · BCR 32 · BBS 2025 Release · 1966–2024

Tree Swallow In Coastal California

All regionsCoastal CaliforniaAerial insectivores

Tree Swallow in Coastal California has surged: up 158% on the route-weighted index since 1970.

+158%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 →
83Routes In RegionSurvey 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 SignalsNotable 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 →

Tree Swallow has surged in Coastal California: up 158% on the route-weighted index since 1970.

Tree Swallow In Coastal California Population Forecast

If the recent trend holds, Tree Swallow in Coastal California is projected to stay roughly flat through 2029, near 4.6 (95% range 1.2–8.0). A 5-year backtest shows a typical error of ±72.6%, with 100% of held-out values landing inside the 95% band.

-7%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 →
4.6Projected 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 →
1.2–8.095% 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 →
±72.6%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, Tree Swallow in Coastal California is projected to stay roughly flat through 2029, near 4.6 (95% range 1.2–8.0). A 5-year backtest shows a typical error of ±72.6%, 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 →
20254.41.07.8
20264.41.17.8
20274.51.17.9
20284.51.27.9
20294.61.28.0

Routes In Coastal California

Routes recording Tree Swallow in Coastal 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 →
OrovilleCALIFORNIA892024
GlennCALIFORNIA702023
AuburnCALIFORNIA411980
MoragaCALIFORNIA362024
El ToroCALIFORNIA231984
CoyoteCALIFORNIA202024
OnoCALIFORNIA182012
OrlandCALIFORNIA142022
CordovaCALIFORNIA131980
Yokohl ValCALIFORNIA111997
CopperopolisCALIFORNIA112024
Tres Pinos 2CALIFORNIA102010
Glen Ellen 2CALIFORNIA102023
CoalingaCALIFORNIA92022
ZamoraCALIFORNIA92024
WestleyCALIFORNIA82024
GravesboroCALIFORNIA71995
Morro BayCALIFORNIA72006
Point ReyesCALIFORNIA72023
SangerCALIFORNIA72024
CrestonCALIFORNIA72024
Gold HillCALIFORNIA72024
StonyfordCALIFORNIA72018
CalpellaCALIFORNIA61986
PenningtonCALIFORNIA62024

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