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

Forster's Tern Population Trend in Wisconsin

All statesWetland birds

Forster's Tern in Wisconsin has edged down: down 24% on the route-weighted index since 1974.

-24%Since 1974TrendPercent 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 →
12Routes 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 →
48YearsYears 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 WisconsinNotable 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 Wisconsin. See the full index history below.

Forster's Tern Population Forecast in Wisconsin

If the recent trend holds, Forster's Tern in Wisconsin is projected to stay roughly flat through 2029, near 0.01 (95% range 0.00–0.22). A 5-year backtest shows a typical error of ±170.4%, 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 →
0.01Projected 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 →
0.00–0.2295% 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 →
±170.4%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 Wisconsin is projected to stay roughly flat through 2029, near 0.01 (95% range 0.00–0.22). A 5-year backtest shows a typical error of ±170.4%, with 100% of held-out values landing inside the 95% band.19722029
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 →
20250.030.000.23
20260.020.000.23
20270.020.000.23
20280.020.000.22
20290.010.000.22

Forster's Tern Survey Routes in Wisconsin

Routes recording Forster's Tern in Wisconsin.
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 →
Casco419891989
Omro320011972
Rolling Pr320101995
Washington I319741974
Hudson219861986
Rib Lake220082008
Briggsville220052005
Bayfield120082008
Manawa120012001
Omro 2120222002
Pardeeville120241992
Brownsville120081975

Forster's Tern Population Trend in Other States

alabamacaliforniacoloradodelawarefloridageorgiaidahoillinoisindianaiowakansaslouisianamarylandmichiganminnesotamontananebraskanevadanew-jerseynew-yorknorth-carolinanorth-dakotaoregonsouth-carolinasouth-dakotatexasutahvirginiawashingtonwyoming

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