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

Forster's Tern Population Trend in North Dakota

All statesWetland birds

Forster's Tern in North Dakota has surged: up 11× on the route-weighted index since 1981.

11×Since 1981TrendPercent 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 →
18Routes 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 →
36YearsYears 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 North DakotaNotable 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 increasecomputed 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 surged in North Dakota: up 11× on the route-weighted index since 1981.

Forster's Tern Population Forecast in North Dakota

If the recent trend holds, Forster's Tern in North Dakota is projected to fall about 55% by 2029 — from 1.7 in 2024 to a central estimate of 0.75 (95% range 0.00–1.6). A 5-year backtest shows a typical error of ±80.9%, with 60% of held-out values landing inside the 95% band.

-55%Change 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 →
0.75Projected 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 →
0.00–1.695% 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 →
±80.9%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, Forster's Tern in North Dakota is projected to fall about 55% by 2029 — from 1.7 in 2024 to a central estimate of 0.75 (95% range 0.00–1.6). A 5-year backtest shows a typical error of ±80.9%, with 60% of held-out values landing inside the 95% band.19692029
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 →
20250.690.001.6
20260.710.001.6
20270.720.001.6
20280.740.001.6
20290.750.001.6

Forster's Tern Survey Routes in North Dakota

Routes recording Forster's Tern in North 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 →
Horsehead Lk4420241981
Lakota 2420162013
Lake George320181997
Danzig220052004
Danzig 2220232019
Forman120091969
Glen Ullin119901990
Wild Rose120012001
Cooperstown120232023
Wimbledon120132013
Buchanan120212003
Powers Lake120192017
Douglas Crk120181984
Sheyenne Lk120241994
Braddock120211997
Turtle Mtns120192001
Niles120222022
Denbigh119911977

Forster's Tern Population Trend in Other States

alabamacaliforniacoloradodelawarefloridageorgiaidahoillinoisindianaiowakansaslouisianamarylandmichiganminnesotamontananebraskanevadanew-jerseynew-yorknorth-carolinaoregonsouth-carolinasouth-dakotatexasutahvirginiawashingtonwisconsinwyoming

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