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

Forster's Tern Population Trend in Colorado

All statesWetland birds

Forster's Tern in Colorado has collapsed: down 77% on the route-weighted index since 1992.

-77%Since 1992TrendPercent 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 →
5Routes 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 →
19YearsYears 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 ColoradoNotable 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 Colorado: down 77% on the route-weighted index since 1992.

Forster's Tern Population Forecast in Colorado

If the recent trend holds, Forster's Tern in Colorado is projected to stay roughly flat through 2021, near 0.03 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±95%, with 80% of held-out values landing inside the 95% band.

n/aChange by 2021TrendPercent 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 →
0.03Projected 2021 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.1195% 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 →
±95%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 Colorado is projected to stay roughly flat through 2021, near 0.03 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±95%, with 80% of held-out values landing inside the 95% band.19902021
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 →
20170.030.000.11
20180.030.000.11
20190.030.000.11
20200.030.000.11
20210.030.000.11

Forster's Tern Survey Routes in Colorado

Routes recording Forster's Tern in Colorado.
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 →
Neegrande419971997
Fort Morgan319961996
Walden220161990
Julesburg120092009
Haswell119991997

Forster's Tern Population Trend in Other States

alabamacaliforniadelawarefloridageorgiaidahoillinoisindianaiowakansaslouisianamarylandmichiganminnesotamontananebraskanevadanew-jerseynew-yorknorth-carolinanorth-dakotaoregonsouth-carolinasouth-dakotatexasutahvirginiawashingtonwisconsinwyoming

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