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Species · Delaware · BBS 2025 Release · 1966–2024

Great Black-backed Gull Population Trend in Delaware

All statesWetland birds

Great Black-backed Gull in Delaware has fallen sharply: down 67% on the route-weighted index since 1968.

-67%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 →
8Routes 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 →
28YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Great Black-backed Gull 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 →

Great Black-backed Gull has fallen sharply in Delaware: down 67% on the route-weighted index since 1968.

Great Black-backed Gull Population Forecast in Delaware

If the recent trend holds, Great Black-backed Gull in Delaware is projected to fall about 100% by 2022 — from 0.33 in 2017 to a central estimate of 0.00 (95% range 0.00–2.6). A 5-year backtest shows a typical error of ±152.8%, with 100% of held-out values landing inside the 95% band.

-100%Change by 2022TrendPercent 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 2022 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–2.695% 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 →
±152.8%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, Great Black-backed Gull in Delaware is projected to fall about 100% by 2022 — from 0.33 in 2017 to a central estimate of 0.00 (95% range 0.00–2.6). A 5-year backtest shows a typical error of ±152.8%, with 100% of held-out values landing inside the 95% band.19662022
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 →
20180.000.002.6
20190.000.002.6
20200.000.002.6
20210.000.002.6
20220.000.002.6

Great Black-backed Gull Survey Routes in Delaware

Routes recording Great Black-backed Gull 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 Bch319901966
Milton319771971
Harrington220171967
Pepperbox220052005
Dover119771972
Lowes Xrds119781978
Blackbird120152001
Holleyville 2120062006

Great Black-backed Gull Population Trend in Other States

connecticutmainemarylandmassachusettsnew-hampshirenew-jerseynew-yorknorth-carolinaohiorhode-islandvermontvirginia

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