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Species · Delaware · BBS 2026 Release · 1966–2025

Prothonotary Warbler Population Trend in Delaware

All statesForest birds

Prothonotary Warbler in Delaware has surged: up 370% on the route-weighted index since 1968.

+370%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 →
13Routes 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 →
56YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Prothonotary Warbler 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 →

Prothonotary Warbler has surged in Delaware: up 370% on the route-weighted index since 1968.

Prothonotary Warbler Population Forecast in Delaware

If the recent trend holds, Prothonotary Warbler in Delaware is projected to fall about 43% by 2030 — from 2.2 in 2025 to a central estimate of 1.2 (95% range 0.37–2.1). A 5-year backtest shows a typical error of ±46.6%, with 40% of held-out values landing inside the 95% band.

-43%Change by 2030TrendPercent 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 →
1.2Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.37–2.195% 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 →
±46.6%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, Prothonotary Warbler in Delaware is projected to fall about 43% by 2030 — from 2.2 in 2025 to a central estimate of 1.2 (95% range 0.37–2.1). A 5-year backtest shows a typical error of ±46.6%, with 40% of held-out values landing inside the 95% band.19662030
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 →
20261.20.312.0
20271.20.322.1
20281.20.342.1
20291.20.352.1
20301.20.372.1

Prothonotary Warbler Survey Routes in Delaware

Routes recording Prothonotary Warbler 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 21020252017
Pepperbox420161998
Mt Pleasant119681968
Wilmington120052005
Harrington120251983
Frederica120111977
Frankford120121966
Holleyville120041975
Lowes Xrds119871966
Milton120131987
Millsboro120252025
Holleyville 2120092008
Milton 2120252017

Prothonotary Warbler Population Trend in Other States

alabamaarkansasfloridageorgiaillinoisindianaiowakansaskentuckylouisianamarylandmichiganminnesotamississippimissourinew-jerseynew-yorknorth-carolinaohiooklahomapennsylvaniasouth-carolinatennesseetexasvirginiawest-virginiawisconsin

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.