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

Willow Flycatcher Population Trend in Delaware

All statesAerial insectivores

Willow Flycatcher in Delaware has risen sharply: up 63% on the route-weighted index since 1978.

+63%Since 1978TrendPercent 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 →
7Routes 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 →
39YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Willow Flycatcher 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 →

Willow Flycatcher has risen sharply in Delaware: up 63% on the route-weighted index since 1978.

Willow Flycatcher Population Forecast in Delaware

If the recent trend holds, Willow Flycatcher in Delaware is projected to rise about 126% by 2029 — from 0.20 in 2024 to a central estimate of 0.45 (95% range 0.11–0.80). A 5-year backtest shows a typical error of ±143.5%, with 40% of held-out values landing inside the 95% band.

+126%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 →
0.45Projected 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 →
0.11–0.8095% 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 →
±143.5%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, Willow Flycatcher in Delaware is projected to rise about 126% by 2029 — from 0.20 in 2024 to a central estimate of 0.45 (95% range 0.11–0.80). A 5-year backtest shows a typical error of ±143.5%, with 40% of held-out values landing inside the 95% band.19762029
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 →
20250.430.090.78
20260.440.090.79
20270.440.100.79
20280.450.100.79
20290.450.110.80

Willow Flycatcher Survey Routes in Delaware

Routes recording Willow Flycatcher 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 →
Mt Pleasant119761976
Wilmington120101978
Harrington120241980
Frederica120101977
Blackbird120231995
Holleyville 2120072007
Georgetown120122004

Willow Flycatcher Population Trend in Other States

alaskaarizonaarkansascaliforniacoloradoconnecticutgeorgiaidahoillinoisindianaiowakansaskentuckymainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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