BirdAnalyst
Species · BCR 32 · BBS 2026 Release · 1966–2025

Tree Swallow In Coastal California

All regionsCoastal CaliforniaAerial insectivores

Tree Swallow in Coastal California has surged: up 218% on the route-weighted index since 1970.

+218%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 →
84Routes 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 →
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 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 218% 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 fall about 12% by 2030 — from 5.3 in 2025 to a central estimate of 4.7 (95% range 1.4–8.1). A 5-year backtest shows a typical error of ±61.5%, with 100% of held-out values landing inside the 95% band.

-12%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 →
4.7Projected 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 →
1.4–8.195% 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 →
±61.5%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 fall about 12% by 2030 — from 5.3 in 2025 to a central estimate of 4.7 (95% range 1.4–8.1). A 5-year backtest shows a typical error of ±61.5%, 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 →
20264.51.27.9
20274.61.27.9
20284.61.38.0
20294.71.38.0
20304.71.48.1

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 →
GlennCALIFORNIA612025
AuburnCALIFORNIA411980
CoyoteCALIFORNIA402025
OrovilleCALIFORNIA312025
El ToroCALIFORNIA231984
OnoCALIFORNIA182012
OrlandCALIFORNIA142022
AdelaidaCALIFORNIA142025
CordovaCALIFORNIA131980
ZamoraCALIFORNIA122025
Yokohl ValCALIFORNIA111997
MoragaCALIFORNIA112025
CopperopolisCALIFORNIA112024
Tres Pinos 2CALIFORNIA102010
Glen Ellen 2CALIFORNIA102023
CoalingaCALIFORNIA92022
GravesboroCALIFORNIA71995
Morro BayCALIFORNIA72006
SangerCALIFORNIA72024
CrestonCALIFORNIA72024
Staten Is.CALIFORNIA72025
StonyfordCALIFORNIA72018
CalpellaCALIFORNIA61986
TehamaCALIFORNIA62005
OnealsCALIFORNIA62024

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