BirdAnalyst
Species · Washington · BBS 2025 Release · 1966–2024

Caspian Tern Population Trend in Washington

All statesWetland birds

Caspian Tern in Washington has edged down: down 11% on the route-weighted index since 1979.

-11%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 →
45YearsYears 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 →

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

Caspian Tern Population Forecast in Washington

If the recent trend holds, Caspian Tern in Washington is projected to rise about 704% by 2029 — from 0.07 in 2024 to a central estimate of 0.56 (95% range 0.04–1.1). A 5-year backtest shows a typical error of ±258.4%, with 80% of held-out values landing inside the 95% band.

+704%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 →
0.56Projected 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 →
0.04–1.195% 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 →
±258.4%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 Washington is projected to rise about 704% by 2029 — from 0.07 in 2024 to a central estimate of 0.56 (95% range 0.04–1.1). A 5-year backtest shows a typical error of ±258.4%, with 80% of held-out values landing inside the 95% band.19712029
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 →
20250.540.021.1
20260.550.031.1
20270.550.031.1
20280.560.041.1
20290.560.041.1

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
Mukilteo320231994
Warm Beach 2320242018
Warm Beach220171991
Hanford Site219961991
Deception219971993
Columbia Nwr220221992
Quincy220121987
Ewan220191999
South Elma219901990
Ellensburg220092001
Horn Rapids220192006
Odessa220072002
Lake Chelan219961996
Taholah120171971
Turnbull Nwr119991999
Vashon Is.120231997
Ilwaco120241979
Keystone120161994

Caspian Tern Population Trend in Other States

alabamaalaskacaliforniadelawarefloridaidahoillinoisindianalouisianamarylandmichiganminnesotamontananevadanorth-carolinanorth-dakotaoregonsouth-carolinatexasutahvermontvirginiawisconsinwyoming

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