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Species · Pennsylvania · BBS 2025 Release · 1966–2024

Tree Swallow Population Trend in Pennsylvania

All statesAerial insectivores

Tree Swallow in Pennsylvania has surged: up 198% on the route-weighted index since 1968.

+198%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 →
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 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 198% 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 74% by 2029 — from 3.5 in 2024 to a central estimate of 6.1 (95% range 2.9–9.3). A 5-year backtest shows a typical error of ±106.3%, with 20% of held-out values landing inside the 95% band.

+74%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 →
6.1Projected 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 →
2.9–9.395% 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 →
±106.3%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 74% by 2029 — from 3.5 in 2024 to a central estimate of 6.1 (95% range 2.9–9.3). A 5-year backtest shows a typical error of ±106.3%, with 20% 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 →
20255.82.79.0
20265.92.79.1
20276.02.89.2
20286.02.99.2
20296.12.99.3

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 →
Brunnerville 22920242010
Ryde2720051981
Betula2020221974
Sugar Grove1720241980
Susquehanna1620241971
Hometown1320241967
Ellenton1220241984
Rush1120241970
Drehersville1119981983
Doe Run1120241979
Berwick1120241986
Marsh Hill1020241983
Honesdale1020241973
Schaefferstown 21020242002
Akeley919791968
Roulette920211971
Hop Bottom920241967
Portersville919881976
Pine Gr Mill920241985
Pottersdale820241988
Logue820231974
Brunnerville820091973
Canadensis720241969
Poyntelle720241969
Ltl Pine Cr720241990

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 2026-05-22.