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Species · Delaware · BBS 2025 Release · 1966–2024

Worm-eating Warbler Population Trend in Delaware

All statesForest birds

Worm-eating Warbler in Delaware has surged: up 442% on the route-weighted index since 1971.

+442%Since 1971TrendPercent 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 →
47YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Worm-eating 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 →

Worm-eating Warbler has surged in Delaware: up 442% on the route-weighted index since 1971.

Worm-eating Warbler Population Forecast in Delaware

If the recent trend holds, Worm-eating Warbler in Delaware is projected to stay roughly flat through 2029, near 1.3 (95% range 0.22–2.4). A 5-year backtest shows a typical error of ±39.6%, with 80% of held-out values landing inside the 95% band.

+8%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 →
1.3Projected 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 →
0.22–2.495% 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 →
±39.6%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, Worm-eating Warbler in Delaware is projected to stay roughly flat through 2029, near 1.3 (95% range 0.22–2.4). A 5-year backtest shows a typical error of ±39.6%, with 80% 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 →
20251.20.142.3
20261.20.162.3
20271.30.182.3
20281.30.202.4
20291.30.222.4

Worm-eating Warbler Survey Routes in Delaware

Routes recording Worm-eating 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 2420242017
Pepperbox320161998
Harrington220161969
Millsboro220242017
Holleyville 2220152015
Frederica120121991
Frankford120121966
Holleyville120001969
Lowes Xrds119911969
Blackbird120182018
Milton120141979
Georgetown120221992
Milton 2120172017

Worm-eating Warbler Population Trend in Other States

alabamaarkansasconnecticutgeorgiaillinoisindianaiowakentuckylouisianamarylandmassachusettsmississippimissourinew-hampshirenew-jerseynew-yorknorth-carolinaohiooklahomapennsylvaniarhode-islandsouth-carolinatennesseetexasvirginiawest-virginiawisconsin

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