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

Least Tern Population Trend in Delaware

All statesWetland birds

Least Tern in Delaware has collapsed: down 88% on the route-weighted index since 1968.

-88%Since 1968TrendPercent 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 →
7Routes 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 →
25YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Least 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 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 →

Least Tern has collapsed in Delaware: down 88% on the route-weighted index since 1968.

Least Tern Population Forecast in Delaware

If the recent trend holds, Least Tern in Delaware is projected to fall about 100% by 2023 — from 0.50 in 2018 to a central estimate of 0.00 (95% range 0.00–4.9). A 5-year backtest shows a typical error of ±268.9%, with 100% of held-out values landing inside the 95% band.

-100%Change by 2023TrendPercent 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 →
0.00Projected 2023 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–4.995% 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 →
±268.9%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, Least Tern in Delaware is projected to fall about 100% by 2023 — from 0.50 in 2018 to a central estimate of 0.00 (95% range 0.00–4.9). A 5-year backtest shows a typical error of ±268.9%, with 100% of held-out values landing inside the 95% band.19662023
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 →
20190.000.004.9
20200.000.004.9
20210.000.004.9
20220.000.004.9
20230.000.004.9

Least Tern Survey Routes in Delaware

Routes recording Least 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 →
Bethany Bch2119901966
Lowes Xrds2019871968
Harrington320181966
Blackbird319981998
Dover219741974
Milton219711971
Georgetown119941994

Least Tern Population Trend in Other States

alabamaarkansascaliforniacoloradofloridageorgiaillinoiskansaskentuckylouisianamainemarylandmassachusettsmississippimissourinebraskanew-jerseynew-yorknorth-carolinaoklahomasouth-carolinatennesseetexasvirginia

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