Tree Swallow
Tree Swallow has held roughly steady: up 0% on the route-weighted index since 1968.
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 Trends
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.
| Year | Projected index | 95% low | 95% high |
|---|---|---|---|
| 2025 | 2.7 | 2.0 | 3.5 |
| 2026 | 2.7 | 2.0 | 3.5 |
| 2027 | 2.7 | 2.0 | 3.5 |
| 2028 | 2.7 | 2.0 | 3.5 |
| 2029 | 2.7 | 2.0 | 3.5 |
Where the Tree Swallow Is Detected
BBS routes recording Tree Swallow, sized by most recent count.
Tree Swallow Population Trend by State
| Alabama | +300% | 1996 | 37 |
| Alaska | +90% | 1973 | 115 |
| Arizona | -86% | 2000 | 8 |
| Arkansas | +73% | 1983 | 24 |
| California | +63% | 1970 | 173 |
| Colorado | +40% | 1970 | 106 |
| Connecticut | +13% | 1968 | 20 |
| Delaware | +729% | 1968 | 17 |
| Florida | insufficient data | n/a | 7 |
| Georgia | +629% | 1991 | 25 |
| Idaho | +68% | 1970 | 53 |
| Illinois | +140% | 1969 | 99 |
| Indiana | +699% | 1976 | 67 |
| Iowa | 12× | 1970 | 37 |
| Kansas | +671% | 1977 | 33 |
| Kentucky | 35× | 1985 | 46 |
| Louisiana | insufficient data | n/a | 4 |
| Maine | -87% | 1968 | 77 |
| Maryland | +518% | 1968 | 71 |
| Massachusetts | -26% | 1968 | 32 |
| Michigan | -6% | 1968 | 104 |
| Minnesota | +69% | 1969 | 91 |
| Mississippi | +315% | 2007 | 11 |
| Missouri | +161% | 1974 | 70 |
| Montana | +112% | 1970 | 100 |
| Nebraska | 12× | 1990 | 49 |
| Nevada | -83% | 1973 | 14 |
| New Hampshire | -69% | 1968 | 26 |
| New Jersey | +40% | 1968 | 39 |
| New Mexico | +123% | 1970 | 12 |
| New York | -8% | 1968 | 129 |
| North Carolina | 22× | 1972 | 56 |
| North Dakota | +952% | 1969 | 48 |
| Ohio | +552% | 1968 | 81 |
| Oklahoma | +953% | 2000 | 8 |
| Oregon | -31% | 1970 | 115 |
| Pennsylvania | +198% | 1968 | 127 |
| Rhode Island | -60% | 1972 | 6 |
| South Carolina | insufficient data | n/a | 5 |
| South Dakota | +612% | 1970 | 53 |
| Tennessee | 15× | 1992 | 39 |
| Texas | -83% | 1990 | 17 |
| Utah | -82% | 1970 | 66 |
| Vermont | -72% | 1968 | 26 |
| Virginia | 26× | 1972 | 66 |
| Washington | -7% | 1970 | 93 |
| West Virginia | 23× | 1977 | 59 |
| Wisconsin | -30% | 1968 | 98 |
| Wyoming | +71% | 1970 | 91 |
Tree Swallow Population Trend by Region
Bird Conservation Regions are the ecological unit for trends.
| BCR 2 | +40% | 1986 | 22 |
| BCR 4 | -83% | 1976 | 59 |
| Northern Pacific Rainforest | -43% | 1970 | 149 |
| Great Basin | +45% | 1970 | 167 |
| Northern Rockies | +32% | 1970 | 183 |
| Prairie Potholes | +615% | 1969 | 112 |
| Boreal Hardwood Transition | -71% | 1968 | 122 |
| Lower Great Lakes / St. Lawrence Plain | -3% | 1968 | 86 |
| Atlantic Northern Forest | -73% | 1968 | 155 |
| Sierra Nevada | +94% | 1970 | 30 |
| Southern Rockies / Colorado Plateau | -21% | 1970 | 154 |
| Badlands and Prairies | +875% | 1971 | 101 |
| Shortgrass Prairie | +855% | 1993 | 24 |
| Central Mixed Grass Prairie | 19× | 1977 | 47 |
| Eastern Tallgrass Prairie | +940% | 1968 | 249 |
| Prairie Hardwood Transition | +131% | 1968 | 161 |
| Central Hardwoods | 37× | 1978 | 125 |
| West Gulf Coastal Plain / Ouachitas | +48% | 1993 | 16 |
| Mississippi Alluvial Valley | +138% | 1975 | 24 |
| Southeastern Coastal Plain | +529% | 1982 | 59 |
| Appalachian Mountains | +236% | 1968 | 339 |
| Piedmont | 34× | 1971 | 103 |
| New England / Mid-Atlantic Coast | +17% | 1968 | 153 |
| Coastal California | +158% | 1970 | 83 |
| Sonoran and Mojave Deserts | -34% | 1976 | 5 |
| Sierra Madre Occidental | -68% | 2008 | 4 |
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.