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

Tree Swallow Population Trend in Delaware

All statesAerial insectivores

Tree Swallow in Delaware has surged: up 729% on the route-weighted index since 1968.

+729%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 →
17Routes 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 →
57YearsYears 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 DelawareNotable 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 Delaware: up 729% on the route-weighted index since 1968.

Tree Swallow Population Forecast in Delaware

If the recent trend holds, Tree Swallow in Delaware is projected to rise about 81% by 2029 — from 4.2 in 2024 to a central estimate of 7.6 (95% range 3.7–11). A 5-year backtest shows a typical error of ±72.8%, with 40% of held-out values landing inside the 95% band.

+81%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 →
7.6Projected 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 →
3.7–1195% 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 →
±72.8%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 Delaware is projected to rise about 81% by 2029 — from 4.2 in 2024 to a central estimate of 7.6 (95% range 3.7–11). A 5-year backtest shows a typical error of ±72.8%, with 40% 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 →
20257.13.211
20267.23.411
20277.33.511
20287.53.611
20297.63.711

Tree Swallow Survey Routes in Delaware

Routes recording Tree Swallow in Delaware.
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 →
Wilmington1820141967
Georgetown1820221995
Frederica1020141994
Harrington820241966
Blackbird620241994
Milton520161974
Mt Pleasant420191971
Holleyville420031975
Holleyville 2420242007
Bethany Bch319901966
Millsboro320172017
Pepperbox 2320242018
Dover219871967
Lowes Xrds219911969
Pepperbox220161998
Milton 2220172017
Frankford120121969

Tree Swallow Population Trend in Other States

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

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