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

Prothonotary Warbler Population Trend in Delaware

All statesForest birds

Prothonotary Warbler in Delaware has surged: up 297% on the route-weighted index since 1968.

+297%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 →
12Routes 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 →
55YearsYears 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 297% 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 36% by 2029 — from 1.8 in 2024 to a central estimate of 1.2 (95% range 0.32–2.0). A 5-year backtest shows a typical error of ±40.9%, with 60% of held-out values landing inside the 95% band.

-36%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 →
1.2Projected 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 →
0.32–2.095% 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 →
±40.9%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, Prothonotary Warbler in Delaware is projected to fall about 36% by 2029 — from 1.8 in 2024 to a central estimate of 1.2 (95% range 0.32–2.0). A 5-year backtest shows a typical error of ±40.9%, 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 →
20251.10.261.9
20261.10.281.9
20271.10.292.0
20281.10.302.0
20291.20.322.0

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 2820242017
Pepperbox420161998
Milton 2220172017
Mt Pleasant119681968
Wilmington120052005
Harrington120241983
Frederica120111977
Frankford120121966
Holleyville120041975
Lowes Xrds119871966
Milton120131987
Holleyville 2120092008

Prothonotary Warbler Population Trend in Other States

alabamaarkansasfloridageorgiaillinoisindianaiowakansaskentuckylouisianamarylandmichiganminnesotamississippimissourinew-jerseynew-yorknorth-carolinaohiooklahomapennsylvaniasouth-carolinatennesseetexasvirginiawest-virginiawisconsin

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