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

Forster's Tern Population Trend in Washington

All statesWetland birds

Forster's Tern in Washington has fallen sharply: down 64% on the route-weighted index since 1991.

-64%Since 1991TrendPercent 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 →
8Routes 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 →
23YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Forster's 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 →

Forster's Tern has fallen sharply in Washington: down 64% on the route-weighted index since 1991.

Forster's Tern Population Forecast in Washington

If the recent trend holds, Forster's Tern in Washington is projected to stay roughly flat through 2027, near 0.00 (95% range 0.00–0.27). A 5-year backtest shows a typical error of ±200.6%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2027TrendPercent 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 →
0.00Projected 2027 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.2795% 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 →
±200.6%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, Forster's Tern in Washington is projected to stay roughly flat through 2027, near 0.00 (95% range 0.00–0.27). A 5-year backtest shows a typical error of ±200.6%, with 100% of held-out values landing inside the 95% band.19892027
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 →
20230.010.000.28
20240.000.000.27
20250.000.000.27
20260.000.000.27
20270.000.000.27

Forster's Tern Survey Routes in Washington

Routes recording Forster's 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 →
Columbia Nwr620211997
Moses Lake520211989
Hanford Site319961991
Bunker Hill119961996
Mesa119951995
Mercer119961996
Horn Rapids120222006
Potholes119971996

Forster's Tern Population Trend in Other States

alabamacaliforniacoloradodelawarefloridageorgiaidahoillinoisindianaiowakansaslouisianamarylandmichiganminnesotamontananebraskanevadanew-jerseynew-yorknorth-carolinanorth-dakotaoregonsouth-carolinasouth-dakotatexasutahvirginiawisconsinwyoming

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