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

Caspian Tern In Coastal California

All regionsCoastal CaliforniaWetland birds

Caspian Tern in Coastal California has edged down: down 20% on the route-weighted index since 1970.

-20%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 →
31Routes 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 →
55YearsYears 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 →

No notable trend signals for Caspian Tern in Coastal California. See the full index history below.

Caspian Tern In Coastal California Population Forecast

If the recent trend holds, Caspian Tern in Coastal California is projected to rise about 51% by 2029 — from 0.38 in 2024 to a central estimate of 0.58 (95% range 0.00–1.6). A 5-year backtest shows a typical error of ±1436.4%, with 100% of held-out values landing inside the 95% band.

+51%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 →
0.58Projected 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 →
0.00–1.695% 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 →
±1436.4%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, Caspian Tern in Coastal California is projected to rise about 51% by 2029 — from 0.38 in 2024 to a central estimate of 0.58 (95% range 0.00–1.6). A 5-year backtest shows a typical error of ±1436.4%, 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 →
20250.550.001.5
20260.560.001.5
20270.570.001.5
20280.570.001.6
20290.580.001.6

Routes In Coastal California

Routes recording Caspian Tern 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 →
Harbor Lake 2CALIFORNIA152024
AdelaidaCALIFORNIA81992
ColmaCALIFORNIA61972
CollegevilleCALIFORNIA21977
Foster ParkCALIFORNIA21974
S CatalinaCALIFORNIA22017
WestleyCALIFORNIA22018
MoragaCALIFORNIA22019
Buena VistaCALIFORNIA22019
PenningtonCALIFORNIA11978
RiovistaCALIFORNIA12024
HughsonCALIFORNIA12010
Harbor LakeCALIFORNIA11989
MorenoCALIFORNIA12017
San YsidroCALIFORNIA12017
HollisterCALIFORNIA12006
Lake SuccessCALIFORNIA11981
Morro BayCALIFORNIA11993
Point ReyesCALIFORNIA12021
FairfaxCALIFORNIA12024
PowayCALIFORNIA11980
ShafterCALIFORNIA11987
GlennCALIFORNIA11993
AtwaterCALIFORNIA11986
OrovilleCALIFORNIA12009

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