BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Tree Swallow

HirundinidaeAerial insectivoresTachycineta bicolor

Tree Swallow has held roughly steady: up 0% on the route-weighted index since 1968.

+0%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 →
2,750RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
58Years SurveyedYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

About the Tree Swallow

An iridescent blue-green cavity nester, the Tree Swallow readily takes to nest boxes and gathers in vast flocks on migration.

Size
4.5–5.5 in long, about 0.7 oz (12–14 cm, 20 g)
Habitat
Open airspace over fields, water and towns; nests in cavities, earthen banks or on structures.
Diet
Flying insects, plus berries (notably bayberry) in cold weather.
Range
Recorded on 2,750 Breeding Bird Survey routes across 49 states, most concentrated in the Appalachian Mountains.
Family
Hirundinidae · Aerial insectivores
Conservation
Least Concern

Notable Tree Swallow TrendsNotable 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. See the full index history below.

Tree Swallow Population Forecast

If the recent trend holds, Tree Swallow is projected to rise about 20% by 2029 — from 2.3 in 2024 to a central estimate of 2.7 (95% range 2.0–3.5). A 5-year backtest shows a typical error of ±36.9%, with 20% of held-out values landing inside the 95% band.

+20%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 →
2.7Projected 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 →
2.0–3.595% 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 →
±36.9%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 is projected to rise about 20% by 2029 — from 2.3 in 2024 to a central estimate of 2.7 (95% range 2.0–3.5). A 5-year backtest shows a typical error of ±36.9%, 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 →
20252.72.03.5
20262.72.03.5
20272.72.03.5
20282.72.03.5
20292.72.03.5

Where the Tree Swallow Is Detected

BBS routes recording Tree Swallow, sized by most recent count.

Tree Swallow Population Trend by State

Tree Swallow population trend by state.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Alabama+300%199637
Alaska+90%1973115
Arizona-86%20008
Arkansas+73%198324
California+63%1970173
Colorado+40%1970106
Connecticut+13%196820
Delaware+729%196817
Floridainsufficient datan/a7
Georgia+629%199125
Idaho+68%197053
Illinois+140%196999
Indiana+699%197667
Iowa12×197037
Kansas+671%197733
Kentucky35×198546
Louisianainsufficient datan/a4
Maine-87%196877
Maryland+518%196871
Massachusetts-26%196832
Michigan-6%1968104
Minnesota+69%196991
Mississippi+315%200711
Missouri+161%197470
Montana+112%1970100
Nebraska12×199049
Nevada-83%197314
New Hampshire-69%196826
New Jersey+40%196839
New Mexico+123%197012
New York-8%1968129
North Carolina22×197256
North Dakota+952%196948
Ohio+552%196881
Oklahoma+953%20008
Oregon-31%1970115
Pennsylvania+198%1968127
Rhode Island-60%19726
South Carolinainsufficient datan/a5
South Dakota+612%197053
Tennessee15×199239
Texas-83%199017
Utah-82%197066
Vermont-72%196826
Virginia26×197266
Washington-7%197093
West Virginia23×197759
Wisconsin-30%196898
Wyoming+71%197091

Tree Swallow Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Tree Swallow population trend by Bird Conservation Region.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
BCR 2+40%198622
BCR 4-83%197659
Northern Pacific Rainforest-43%1970149
Great Basin+45%1970167
Northern Rockies+32%1970183
Prairie Potholes+615%1969112
Boreal Hardwood Transition-71%1968122
Lower Great Lakes / St. Lawrence Plain-3%196886
Atlantic Northern Forest-73%1968155
Sierra Nevada+94%197030
Southern Rockies / Colorado Plateau-21%1970154
Badlands and Prairies+875%1971101
Shortgrass Prairie+855%199324
Central Mixed Grass Prairie19×197747
Eastern Tallgrass Prairie+940%1968249
Prairie Hardwood Transition+131%1968161
Central Hardwoods37×1978125
West Gulf Coastal Plain / Ouachitas+48%199316
Mississippi Alluvial Valley+138%197524
Southeastern Coastal Plain+529%198259
Appalachian Mountains+236%1968339
Piedmont34×1971103
New England / Mid-Atlantic Coast+17%1968153
Coastal California+158%197083
Sonoran and Mojave Deserts-34%19765
Sierra Madre Occidental-68%20084

Tree Swallow Conservation Status

Least Concern

The IUCN Red List rates this species as Least Concern. Our route-weighted index has held roughly steady since 1968. Aerial insectivores have fallen sharply across the continent, a decline widely linked to dwindling insect prey.

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22. Trend is a route-weighted relative-abundance index, not an absolute population.