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

Common Tern Population Trend in Delaware

All statesWetland birds

Common Tern in Delaware has collapsed: down 90% on the route-weighted index since 1968.

-90%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 →
5Routes 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 →
21YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Common 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 →

Common Tern has collapsed in Delaware: down 90% on the route-weighted index since 1968.

Common Tern Population Forecast in Delaware

If the recent trend holds, Common Tern in Delaware is projected to fall about 100% by 2019 — from 0.14 in 2014 to a central estimate of 0.00 (95% range 0.00–6.6). A 5-year backtest shows a typical error of ±1378%, with 80% of held-out values landing inside the 95% band.

-100%Change by 2019TrendPercent 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 2019 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–6.695% 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 →
±1378%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, Common Tern in Delaware is projected to fall about 100% by 2019 — from 0.14 in 2014 to a central estimate of 0.00 (95% range 0.00–6.6). A 5-year backtest shows a typical error of ±1378%, with 80% of held-out values landing inside the 95% band.19662019
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 →
20150.000.006.6
20160.000.006.6
20170.000.006.6
20180.000.006.6
20190.000.006.6

Common Tern Survey Routes in Delaware

Routes recording Common 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 →
Milton619751971
Lowes Xrds319911966
Bethany Bch219901966
Dover119771977
Blackbird120142014

Common Tern Population Trend in Other States

alabamaalaskaconnecticutfloridaidahoindianalouisianamainemarylandmassachusettsmichiganminnesotamontananew-jerseynew-yorknorth-carolinanorth-dakotaohiorhode-islandsouth-dakotatexasvermontvirginiawashingtonwisconsinwyoming

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