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Species · Pennsylvania · BBS 2025 Release · 1966–2024

Willow Flycatcher Population Trend in Pennsylvania

All statesAerial insectivores

Willow Flycatcher in Pennsylvania has surged: up 96% on the route-weighted index since 1968.

+96%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 →
118Routes 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 →
58YearsYears 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 PennsylvaniaNotable 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 surged in Pennsylvania: up 96% on the route-weighted index since 1968.

Willow Flycatcher Population Forecast in Pennsylvania

If the recent trend holds, Willow Flycatcher in Pennsylvania is projected to rise about 63% by 2029 — from 1.2 in 2024 to a central estimate of 2.0 (95% range 1.0–3.0). A 5-year backtest shows a typical error of ±73.6%, with 60% of held-out values landing inside the 95% band.

+63%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 →
2.0Projected 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 →
1.0–3.095% 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 →
±73.6%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, Willow Flycatcher in Pennsylvania is projected to rise about 63% by 2029 — from 1.2 in 2024 to a central estimate of 2.0 (95% range 1.0–3.0). A 5-year backtest shows a typical error of ±73.6%, 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 →
20251.90.962.9
20262.00.982.9
20272.00.993.0
20282.01.03.0
20292.01.03.0

Willow Flycatcher Survey Routes in Pennsylvania

Routes recording Willow Flycatcher in Pennsylvania.
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 →
West Grove1419961967
Harmonsburg1220231966
Jefferson720241966
Poyntelle620241975
Beaver620241978
Plesant Grov620241970
Kaylor620241995
Drehersville619991966
Drehersville 2620242000
Ferris Crnrs520241966
Waller520241974
Quakertown519891972
Teepleville420241966
Roulette420161989
Martinsburg420241988
Clover320241988
Millville320241974
Honesdale320241972
Portersville319881974
Parkwood320231967
Kittanning320231973
Brunnerville320091970
Doe Run320241969
Mt Gretna 2320192015
Schaefferstown 2320242008

Willow Flycatcher Population Trend in Other States

alaskaarizonaarkansascaliforniacoloradoconnecticutdelawaregeorgiaidahoillinoisindianaiowakansaskentuckymainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonrhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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