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

Caspian Tern Population Trend in Idaho

All statesWetland birds

Caspian Tern in Idaho has collapsed: down 81% on the route-weighted index since 1986.

-81%Since 1986TrendPercent 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 →
9Routes 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 →
20YearsYears 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 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 →

Caspian Tern has collapsed in Idaho: down 81% on the route-weighted index since 1986.

Caspian Tern Population Forecast in Idaho

If the recent trend holds, Caspian Tern in Idaho is projected to stay roughly flat through 2028, near 0.00 (95% range 0.00–0.09). A 5-year backtest shows a typical error of ±53.9%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2028TrendPercent 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 2028 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.0995% 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 →
±53.9%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, Caspian Tern in Idaho is projected to stay roughly flat through 2028, near 0.00 (95% range 0.00–0.09). A 5-year backtest shows a typical error of ±53.9%, with 100% of held-out values landing inside the 95% band.19732028
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 →
20240.000.000.10
20250.000.000.10
20260.000.000.09
20270.000.000.09
20280.000.000.09

Caspian Tern Survey Routes in Idaho

Routes recording Caspian 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 →
Kyle Canyon319861986
Acequia220022002
Featherville220032000
Cedar Hill120231998
Preston120081992
Cascade119841984
Springfield120161973
Picabo120051996
Pasadena Val120101987

Caspian Tern Population Trend in Other States

alabamaalaskacaliforniadelawarefloridaillinoisindianalouisianamarylandmichiganminnesotamontananevadanorth-carolinanorth-dakotaoregonsouth-carolinatexasutahvermontvirginiawashingtonwisconsinwyoming

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