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Species · Pennsylvania · BBS 2026 Release · 1966–2025

Tree Swallow Population Trend in Pennsylvania

All statesAerial insectivores

Tree Swallow in Pennsylvania has surged: up 201% on the route-weighted index since 1968.

+201%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 →
127Routes 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 →
59YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Tree Swallow 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 →

Tree Swallow has surged in Pennsylvania: up 201% on the route-weighted index since 1968.

Tree Swallow Population Forecast in Pennsylvania

If the recent trend holds, Tree Swallow in Pennsylvania is projected to rise about 105% by 2030 — from 2.9 in 2025 to a central estimate of 6.0 (95% range 2.7–9.2). A 5-year backtest shows a typical error of ±112.7%, with 20% of held-out values landing inside the 95% band.

+105%Change by 2030TrendPercent 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 →
6.0Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
2.7–9.295% 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 →
±112.7%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, Tree Swallow in Pennsylvania is projected to rise about 105% by 2030 — from 2.9 in 2025 to a central estimate of 6.0 (95% range 2.7–9.2). A 5-year backtest shows a typical error of ±112.7%, with 20% of held-out values landing inside the 95% band.19662030
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 →
20265.72.58.9
20275.82.59.0
20285.82.69.1
20295.92.79.1
20306.02.79.2

Tree Swallow Survey Routes in Pennsylvania

Routes recording Tree Swallow 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 →
Ryde2720051981
Betula2020221974
Brunnerville 21720252010
Honesdale1320251973
Wyalusing1220251985
Drehersville1119981983
Pine Gr Mill1020251985
Akeley919791968
Roulette920211971
Portersville919881976
Peru Mills920251968
Ltl Pine Cr920251990
Susquehanna820251971
Brunnerville820091973
Garrett820251966
Hop Bottom720251967
Williamsburg720251991
Akron719971997
Bow Bridge620251969
Mt Gretna620001991
Jefferson620241976
Starlight 2620252000
Pottersdale520251988
English Ctr519891968
Ravensburg519801970

Tree Swallow Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonrhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.