BirdAnalyst
Species · BBS 2026 Release · 1966–2025

Tree Swallow Population Analysis

HirundinidaeAerial insectivoresTachycineta bicolor

Tree Swallow has held roughly steady: up 4% on the route-weighted index since 1968.

+4%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 →
2,770RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
59Years 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 2,770 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 22% by 2030 — from 2.2 in 2025 to a central estimate of 2.7 (95% range 1.9–3.5). A 5-year backtest shows a typical error of ±37.9%, with 20% of held-out values landing inside the 95% band.

+22%Change by 2030TrendPercent 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 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
1.9–3.595% 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 →
±37.9%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 22% by 2030 — from 2.2 in 2025 to a central estimate of 2.7 (95% range 1.9–3.5). A 5-year backtest shows a typical error of ±37.9%, with 20% of held-out values landing inside the 95% band.19662030
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 →
20262.71.93.5
20272.71.93.5
20282.71.93.5
20292.71.93.5
20302.71.93.5

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+469%199637
Alaska+77%1973115
Arizona-81%20008
Arkansas+38%198324
California+89%1970174
Colorado+22%1970107
Connecticut+19%196820
Delaware+670%196817
Floridainsufficient datan/a7
Georgia+330%199127
Idaho+101%197053
Illinois+163%196999
Indiana+781%197667
Iowa25×197037
Kansas+671%197733
Kentucky39×198546
Louisianainsufficient datan/a4
Maine-89%196877
Maryland+535%196871
Massachusetts-32%196832
Michigan+5%1968104
Minnesota+64%196991
Mississippi+375%200711
Missouri+147%197471
Montana+114%1970100
Nebraska12×199052
Nevada-73%197315
New Hampshire-74%196826
New Jersey+42%196839
New Mexico+71%197012
New York-23%1968129
North Carolina24×197256
North Dakota+750%196948
Ohio+602%196881
Oklahoma+953%20008
Oregon-22%1970118
Pennsylvania+201%1968127
Rhode Island-81%19726
South Carolina-26%20126
South Dakota+577%197053
Tennessee14×199240
Texas-83%199018
Utah-80%197066
Vermont-68%196826
Virginia27×197268
Washington-2%197094
West Virginia19×197759
Wisconsin-32%196898
Wyoming+96%197093

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+39%198622
BCR 4-83%197659
Northern Pacific Rainforest-40%1970150
Great Basin+63%1970170
Northern Rockies+40%1970185
Prairie Potholes+520%1969112
Boreal Hardwood Transition-74%1968122
Lower Great Lakes / St. Lawrence Plain-15%196886
Atlantic Northern Forest-75%1968155
Sierra Nevada+60%197030
Southern Rockies / Colorado Plateau-23%1970155
Badlands and Prairies+756%1971102
Shortgrass Prairie+562%199324
Central Mixed Grass Prairie21×197750
Eastern Tallgrass Prairie15×1968250
Prairie Hardwood Transition+148%1968161
Central Hardwoods35×1978125
West Gulf Coastal Plain / Ouachitas+48%199316
Mississippi Alluvial Valley+144%197524
Southeastern Coastal Plain+615%198261
Appalachian Mountains+229%1968340
Piedmont34×1971106
New England / Mid-Atlantic Coast+17%1968153
Coastal California+218%197084
Sonoran and Mojave Deserts-34%19765
Sierra Madre Occidental-62%20084

Tree Swallow Conservation Status

Least Concern

The IUCN Red List rates this species as Least Concern. Our route-weighted index shows it up about 4% 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 2026-08-14. Trend is a route-weighted relative-abundance index, not an absolute population.