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

Tree Swallow Population Trend in Maryland

All statesAerial insectivores

Tree Swallow in Maryland has surged: up 518% on the route-weighted index since 1968.

+518%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 →
71Routes 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 MarylandNotable 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 Maryland: up 518% on the route-weighted index since 1968.

Tree Swallow Population Forecast in Maryland

If the recent trend holds, Tree Swallow in Maryland is projected to rise about 18% by 2029 — from 3.3 in 2024 to a central estimate of 3.9 (95% range 2.9–4.8). A 5-year backtest shows a typical error of ±11.3%, with 100% of held-out values landing inside the 95% band.

+18%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 →
3.9Projected 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 →
2.9–4.895% 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 →
±11.3%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 Maryland is projected to rise about 18% by 2029 — from 3.3 in 2024 to a central estimate of 3.9 (95% range 2.9–4.8). A 5-year backtest shows a typical error of ±11.3%, with 100% 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 →
20253.62.74.5
20263.72.74.6
20273.72.84.7
20283.82.94.7
20293.92.94.8

Tree Swallow Survey Routes in Maryland

Routes recording Tree Swallow in Maryland.
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 →
Madison2920241966
Smithsburg2520131996
Honga2520241968
Jessup1320242015
Earlton1220242014
Van Bibber820131978
Newark620241970
Furnace Town620242017
Wolfsville520241986
Warfieldsbrg520232003
Forest Grove520232011
Vindex420221975
Emmitsburg420241994
Eklo420171997
Accident420151992
Potomac Park320241986
Silver Spg319821977
Olney320241987
Millington320241967
Cokesbury320241973
Severna Park320012001
Williamsport220241992
Pleasant Val220231973
Bachman Mill220221991
Fowblesburg220171994

Tree Swallow Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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