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

Alder Flycatcher Population Trend in Pennsylvania

All statesAerial insectivores

Alder Flycatcher in Pennsylvania has surged: up 287% on the route-weighted index since 1973.

+287%Since 1973TrendPercent 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 →
78Routes 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 →
53YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Alder 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 →

Alder Flycatcher has surged in Pennsylvania: up 287% on the route-weighted index since 1973.

Alder Flycatcher Population Forecast in Pennsylvania

If the recent trend holds, Alder Flycatcher in Pennsylvania is projected to rise about 75% by 2029 — from 0.35 in 2024 to a central estimate of 0.61 (95% range 0.34–0.87). A 5-year backtest shows a typical error of ±79.2%, with 20% of held-out values landing inside the 95% band.

+75%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 →
0.61Projected 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 →
0.34–0.8795% 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 →
±79.2%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, Alder Flycatcher in Pennsylvania is projected to rise about 75% by 2029 — from 0.35 in 2024 to a central estimate of 0.61 (95% range 0.34–0.87). A 5-year backtest shows a typical error of ±79.2%, with 20% of held-out values landing inside the 95% band.19712029
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 →
20250.570.310.84
20260.580.320.84
20270.590.330.85
20280.600.340.86
20290.610.340.87

Alder Flycatcher Survey Routes in Pennsylvania

Routes recording Alder 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 →
Little Marsh820231993
Roulette 2720232022
Eldred620151990
Roulette520211988
Rasselas420221999
Logue420231981
Marsh Hill420241991
Starlight419921992
Greentown420241977
Ellenton420241982
Rush320241971
Poyntelle320241993
Sugar Grove320241995
Ferris Crnrs220241973
Whig Hill220031989
Akeley219761974
Teepleville220231995
N Pine Grove219971997
Betula220221987
Arnot220241982
Mawr Glen220191985
Austinville220241982
New Ringgold219851979
Mars219941994
Espyville120131975

Alder Flycatcher Population Trend in Other States

alaskaconnecticutidahoillinoisindianaiowamainemarylandmassachusettsmichiganminnesotamontananew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiooklahomasouth-dakotavermontvirginiawashingtonwest-virginiawisconsin

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