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

Black Tern In Coastal California

All regionsCoastal CaliforniaWetland birds

Black Tern in Coastal California has fallen sharply: down 75% on the route-weighted index since 1973.

-75%Since 1973TrendPercent 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 →
5Routes 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 →
38YearsYears 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 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 →

Black Tern has fallen sharply in Coastal California: down 75% on the route-weighted index since 1973.

Black Tern In Coastal California Population Forecast

If the recent trend holds, Black Tern in Coastal California is projected to stay roughly flat through 2026, near 0.24 (95% range 0.00–0.64). A 5-year backtest shows a typical error of ±760.9%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2026TrendPercent 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 →
0.24Projected 2026 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.6495% 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 →
±760.9%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, Black Tern in Coastal California is projected to stay roughly flat through 2026, near 0.24 (95% range 0.00–0.64). A 5-year backtest shows a typical error of ±760.9%, with 100% of held-out values landing inside the 95% band.19712026
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 →
20220.230.000.64
20230.240.000.64
20240.240.000.64
20250.240.000.64
20260.240.000.64

Routes In Coastal California

Routes recording Black 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 →
Ora LomaCALIFORNIA431973
OrlandCALIFORNIA21996
GlennCALIFORNIA22021
TranquillityCALIFORNIA21995
HughsonCALIFORNIA11991

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