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

Forster's Tern Population Trend in Idaho

All statesWetland birds

Forster's Tern in Idaho has collapsed: down 89% on the route-weighted index since 1977.

-89%Since 1977TrendPercent 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 →
14Routes 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 →
27YearsYears 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 IdahoNotable 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 collapsed in Idaho: down 89% on the route-weighted index since 1977.

Forster's Tern Population Forecast in Idaho

If the recent trend holds, Forster's Tern in Idaho is projected to stay roughly flat through 2020, near 0.00 (95% range 0.00–0.57). A 5-year backtest shows a typical error of ±464.4%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2020TrendPercent 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 2020 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.5795% 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 →
±464.4%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, Forster's Tern in Idaho is projected to stay roughly flat through 2020, near 0.00 (95% range 0.00–0.57). A 5-year backtest shows a typical error of ±464.4%, with 100% of held-out values landing inside the 95% band.19682020
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 →
20160.000.000.57
20170.000.000.57
20180.000.000.57
20190.000.000.57
20200.000.000.57

Forster's Tern Survey Routes in Idaho

Routes recording Forster's Tern in Idaho.
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 →
Glenns Ferry1019681968
Preston920041990
Triangle520142003
Cedar Hill420142002
Pasadena Val220121987
Picabo220152015
Blackft Res120031985
Tractor Flat120071990
Centerville120112011
Crane Creek119891989
Springfield120071977
Iron Springs119961996
Featherville120101989
Henry119791973

Forster's Tern Population Trend in Other States

alabamacaliforniacoloradodelawarefloridageorgiaillinoisindianaiowakansaslouisianamarylandmichiganminnesotamontananebraskanevadanew-jerseynew-yorknorth-carolinanorth-dakotaoregonsouth-carolinasouth-dakotatexasutahvirginiawashingtonwisconsinwyoming

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