BirdAnalyst
Species · Washington · BBS 2026 Release · 1966–2025

Caspian Tern Population Trend in Washington

All statesWetland birds

Caspian Tern in Washington has fallen sharply: down 53% on the route-weighted index since 1979.

-53%Since 1979TrendPercent 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 →
28Routes 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 →
46YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Caspian Tern Trends in WashingtonNotable 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 →

Caspian Tern has fallen sharply in Washington: down 53% on the route-weighted index since 1979.

Caspian Tern Population Forecast in Washington

If the recent trend holds, Caspian Tern in Washington is projected to rise about 406% by 2030 — from 0.10 in 2025 to a central estimate of 0.53 (95% range 0.00–1.1). A 5-year backtest shows a typical error of ±299%, with 60% of held-out values landing inside the 95% band.

+406%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 →
0.53Projected 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 →
0.00–1.195% 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 →
±299%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 Washington is projected to rise about 406% by 2030 — from 0.10 in 2025 to a central estimate of 0.53 (95% range 0.00–1.1). A 5-year backtest shows a typical error of ±299%, with 60% of held-out values landing inside the 95% band.19712030
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 →
20260.510.001.0
20270.510.001.0
20280.520.001.0
20290.520.001.0
20300.530.001.1

Caspian Tern Survey Routes in Washington

Routes recording Caspian Tern in Washington.
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 →
Tonasket919931993
Port Angeles420232006
Moses Lake420111979
Mcchord419981997
L. Wenatchee420032003
Bunker Hill320001997
Othello319911981
Mukilteo320251994
Warm Beach 2320242018
Warm Beach220171991
Hanford Site219961991
Deception219971993
Columbia Nwr220221992
Quincy220121987
Ewan220191999
Ilwaco220251979
South Elma219901990
Ellensburg220092001
Horn Rapids220192006
Odessa220072002
Lake Chelan219961996
Taholah120171971
Turnbull Nwr119991999
Vashon Is.120231997
Keystone120161994

Caspian Tern Population Trend in Other States

alabamaalaskacaliforniadelawarefloridaidahoillinoisindianalouisianamarylandmichiganminnesotamontananevadanorth-carolinanorth-dakotaoregonsouth-carolinasouth-dakotatexasutahvermontvirginiawisconsinwyoming

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