Tree swallows and barn swallows are two similar-looking bird species that are often found in the same areas during breeding season. This leads many people to wonder – do these two types of swallows get along when their habitats overlap? Or are they competitive with each other?
Quick Facts About Tree Swallows and Barn Swallows
Tree swallows (Tachycineta bicolor) and barn swallows (Hirundo rustica) belong to the family Hirundinidae, which includes all swallows and martins. Here are some key facts about each species:
Tree Swallows
- Small songbird, 5-6 inches long with pointed wings and a forked tail
- Iridescent blue-green upperparts and white underparts
- Found throughout North America near open fields, marshes, and water sources
- Migratory – winters in the southern U.S., Mexico, Central America, and the Caribbean
- Nest in cavities like old woodpecker holes or nest boxes
- Feed exclusively on insects caught during flight
Barn Swallows
- Small songbird, 6-7 inches long with pointed wings and a deeply forked tail
- Iridescent blue upperparts, cinnamon underparts, and a reddish-brown forehead and throat
- Found throughout North America, often around barns and other structures
- Migratory – winters in Central and South America
- Build mud nests lined with feathers and grass on vertical surfaces like cliffs or buildings
- Feed exclusively on insects caught during flight
So while these two species share some common traits, they also have distinct differences when it comes to their plumage, nesting sites, and preferred habitats.
Do Tree Swallows and Barn Swallows Compete for Resources?
Tree swallows and barn swallows rely on many of the same resources. Both species:
- Nest in cavities or artificial nest boxes
- Feed on flying insects like flies, beetles, and ants
- Require open habitat near water for foraging
This means they frequently come into contact and have to share habitat resources during the breeding season. But does this lead to active competition between the two species?
Research suggests tree swallows and barn swallows may compete in some situations, but they have adopted strategies to reduce competition where their ranges overlap:
- Tree swallows start nesting earlier in spring, while barn swallows arrive later from migration. This temporal separation reduces competition for nest sites.
- The two species show different preferences when nesting in boxes – tree swallows prefer boxes over water, while barn swallows prefer boxes on buildings or other structures.
- Barn swallows are more social and nest in colonies, while tree swallows are solitary nesters. Colonies concentrate barn swallow nesting in a few areas.
- Tree swallows and barn swallows forage at slightly different heights and locations. Tree swallows fly lower over fields and marshes. Barn swallows fly higher and closer to structures.
Research has found that reproductive success for both species is actually higher in areas where they overlap. This suggests the separation strategies are generally effective at minimizing direct competition.
Aggressive Interactions Between the Species
While tree swallows and barn swallows have adapted to co-exist, aggressive interactions between the two species may still occur in some situations:
- They may fight over desirable nesting sites. Tree swallows are very defensive of nesting cavities and will harass barn swallows that get too close.
- Swallows may mob or dive at each other when defending feeding territories around nest sites.
- Hybridization between tree swallows and barn swallows is rare but has been documented. This suggests some limited interbreeding where ranges overlap.
However, research indicates these aggressive interactions do not have severe negative impacts on either population overall. Barn swallows in particular have been found to be dominant over tree swallows during aggressive encounters.
Coexistence Through Niche Partitioning
The key to tree swallows and barn swallows minimizing competition appears to be niche partitioning. This refers to adaptation that allows closely related species to avoid competing for identical resources in an environment by occupying different niches.
We see several examples of niche partitioning between tree and barn swallows:
Timing of Breeding
Tree swallows arrive at breeding grounds and begin nesting several weeks before barn swallows. This gives tree swallows first access to nest sites before barn swallows return from migration.
Foraging Locations
While both species feed on flying insects, tree swallows forage predominantly over open water and fields. Barn swallows do more foraging around structures, roads, and livestock.
Nest Site Selection
Tree swallows and barn swallows both readily use artificial nest boxes provided for them. But tree swallows choose boxes located over or very near water. Barn swallows prefer boxes on buildings and other structures, often under eaves.
This separation of nesting and feeding space allows the species to minimize competition in areas where their breeding habitats overlap. It enables both swallow populations to thrive.
Symbiotic Relationship
Recent research has revealed tree swallows and barn swallows may actually benefit from each other’s presence in some cases. A multi-year study in New York state found that barn swallow colonies had a symbiotic relationship with tree swallows nesting nearby:
- Barn swallow colonies were more productive when tree swallows were nesting within 100 meters of the colony.
- Tree swallow reproductive success was also higher near barn swallow colonies.
- The presence of tree swallows may benefit barn swallows by reducing predator pressure near colony sites.
This suggests that tree swallows and barn swallows, rather than being direct competitors, may in some cases have a mutualistic, or symbiotic, relationship that provides protection benefits for both species.
Protecting Both Species
Understanding how tree swallows and barn swallows interact and compete for resources helps inform conservation efforts. Here are some tips for protecting both swallow species where their ranges overlap:
- Preserve mixed open habitats that include wetlands, fields, and human structures like barns. This provides the varied foraging and nesting opportunities the swallows require.
- Consider the preferred nesting locations of each species when putting up nest boxes – tree swallow boxes over water, barn swallow boxes on buildings.
- Avoid using pesticides and preserve wetlands and riparian areas that provide insect prey.
- Maintain healthy populations of both species, which appear to benefit from sharing space in many cases.
Conclusion
Tree swallows and barn swallows have evolved adaptations like temporal separation and niche partitioning that allow them to minimize competition where their breeding ranges overlap. While aggressive interactions may occur, the two species generally co-exist well.
In some cases, the presence of both swallows in an area may even be symbiotic. Preserving the varied habitats both species favor and providing suitable nest sites helps maintain healthy populations of tree swallows and barn swallows across North America.
