BirdAnalyst
Species · South Dakota · BBS 2025 Release · 1966–2024

Forster's Tern Population Trend in South Dakota

All statesWetland birds

Forster's Tern in South Dakota has edged down: down 21% on the route-weighted index since 1969.

-21%Since 1969TrendPercent 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 →
15Routes 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 →
38YearsYears 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 South DakotaNotable 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 Forster's Tern in South Dakota. See the full index history below.

Forster's Tern Population Forecast in South Dakota

If the recent trend holds, Forster's Tern in South Dakota is projected to stay roughly flat through 2029, near 0.06 (95% range 0.00–0.17). A 5-year backtest shows a typical error of ±35.8%, with 100% of held-out values landing inside the 95% band.

n/aChange 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 →
0.06Projected 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 →
0.00–0.1795% 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 →
±35.8%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 South Dakota is projected to stay roughly flat through 2029, near 0.06 (95% range 0.00–0.17). A 5-year backtest shows a typical error of ±35.8%, with 100% of held-out values landing inside the 95% band.19672029
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 →
20250.070.000.17
20260.060.000.17
20270.060.000.17
20280.060.000.17
20290.060.000.17

Forster's Tern Survey Routes in South Dakota

Routes recording Forster's Tern in South Dakota.
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 →
White Lake420111967
Long Lake320171977
Lennox219811981
Fort Pierre219981986
Crow Creek220191969
Veblen220082008
Britton220222001
Gettysburg220131992
Howard119861986
Volga120241969
Roswell119891989
Lacreek119911991
Wilmot119871969
Forbes119791979
Lane 2120122012

Forster's Tern Population Trend in Other States

alabamacaliforniacoloradodelawarefloridageorgiaidahoillinoisindianaiowakansaslouisianamarylandmichiganminnesotamontananebraskanevadanew-jerseynew-yorknorth-carolinanorth-dakotaoregonsouth-carolinatexasutahvirginiawashingtonwisconsinwyoming

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