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

Forster's Tern Population Trend in Delaware

All statesWetland birds

Forster's Tern in Delaware has surged: up 37× on the route-weighted index since 1977.

37×Since 1977TrendPercent 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 →
37YearsYears 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 DelawareNotable 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 Delaware: up 37× on the route-weighted index since 1977.

Forster's Tern Population Forecast in Delaware

If the recent trend holds, Forster's Tern in Delaware is projected to rise about 201% by 2029 — from 1.2 in 2024 to a central estimate of 3.6 (95% range 0.00–7.9). A 5-year backtest shows a typical error of ±111%, with 60% of held-out values landing inside the 95% band.

+201%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 →
3.6Projected 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 →
0.00–7.995% 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 →
±111%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 Delaware is projected to rise about 201% by 2029 — from 1.2 in 2024 to a central estimate of 3.6 (95% range 0.00–7.9). A 5-year backtest shows a typical error of ±111%, with 60% of held-out values landing inside the 95% band.19662029
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 →
20253.30.007.6
20263.40.007.7
20273.50.007.7
20283.50.007.8
20293.60.007.9

Forster's Tern Survey Routes in Delaware

Routes recording Forster's Tern in Delaware.
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 →
Pepperbox 2520242017
Bethany Bch419891985
Pepperbox420161998
Lowes Xrds219911974
Harrington120231992
Dover119661966
Frankford120062006
Blackbird120241994
Georgetown120061992

Forster's Tern Population Trend in Other States

alabamacaliforniacoloradofloridageorgiaidahoillinoisindianaiowakansaslouisianamarylandmichiganminnesotamontananebraskanevadanew-jerseynew-yorknorth-carolinanorth-dakotaoregonsouth-carolinasouth-dakotatexasutahvirginiawashingtonwisconsinwyoming

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