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

Tree Swallow Population Trend in Connecticut

All statesAerial insectivores

Tree Swallow in Connecticut has edged up: up 13% on the route-weighted index since 1968.

+13%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 →
20Routes 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 ConnecticutNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

No notable trend signals for Tree Swallow in Connecticut. See the full index history below.

Tree Swallow Population Forecast in Connecticut

If the recent trend holds, Tree Swallow in Connecticut is projected to rise about 33% by 2029 — from 4.9 in 2024 to a central estimate of 6.5 (95% range 0.55–12). A 5-year backtest shows a typical error of ±109.7%, with 100% of held-out values landing inside the 95% band.

+33%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 →
6.5Projected 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 →
0.55–1295% 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 →
±109.7%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 Connecticut is projected to rise about 33% by 2029 — from 4.9 in 2024 to a central estimate of 6.5 (95% range 0.55–12). A 5-year backtest shows a typical error of ±109.7%, 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 →
20256.30.3712
20266.40.4112
20276.40.4612
20286.50.5012
20296.50.5512

Tree Swallow Survey Routes in Connecticut

Routes recording Tree Swallow in Connecticut.
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 →
Warren1320111972
Sherman920191972
Mid Haddam820241973
Woodstock720071968
Westbrook720241972
Willimantic620181967
No Woodbury620241967
Long Hill620181972
Southington620241973
New Hartford620241994
Buckingham420221966
Uncasville420241979
Warren 2420242012
New Hartford319871972
Mystic220221973
E Hartland219921966
Greenwich220171968
Woodstock 2220242016
Danbury120221968
Granby120241988

Tree Swallow Population Trend in Other States

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

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