Tree swallows breed throughout central and northern North America. The northernmost limit of the tree swallow breeding range coincides approximately with the tree line. Tree swallows winter in southern North America, primarily in Florida, and along the Caribbean coast of Central America.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: BREEDS: western Alaska to Newfoundland, south to southern California, Nevada, Arizona, New Mexico, northeastern Louisiana, western Mississippi, Tennessee and North Carolina, casually to southern states. Range has expanded in southeastern U.S. in recent decades, perhaps facilitated by land clearing, impoundments, beaver reintroduction, and use of bluebird nest boxes (Lee 1993). WINTERS: primarily from southern California and extreme southern U.S. through Mexico to Honduras, Nicaragua and Costa Rica, sporatically to Panama; Bahamas and Greater Antilles (Puerto Rico: rare), rarely to northern South America (Ridgely and Tudor 1989).

Tree Swallows provide an excellent example of countershading (strong dark coloration dorsally and highly contrasted white shading ventrally). Countershading allows for birds to reduce the contrast between their shape and the surrounding environment, therefore aiding in concealment. Generally, greater contrast in coloration of a bird reflects a greater illumination from above (Thayer, 1909).

Tree Swallows are unique in that first year females display delayed plumage maturation, appearing a dull brown dorsally although they are sexually mature. By contrast, first year males do not display delayed plumage maturation and appear blue-green dorsally in their first year. They, too are sexually mature although evidence suggests that they are not as successful as returning males at securing a mate (Thompson, 1991). Although there is no delay in male plumage maturation, it is believed that as males mature, their plumage becomes brighter to optimally reflect light at a shorter wave-length (blue). Additionally, evidence suggests that males who appear more green may express lower nest fidelity and/or a lower survival rate than do their blue counterparts. Therefore both brightness and hue may be reflective of male quality in Tree Swallows (Bitton and Dawson, 2008).

This is further supported by the knowledge that iridescence in color is a function of both the number and quality of feather barbules while hue is a function of the thickness of the feather cortex (Doucet et al., 2006, Prum, 2006). Condition in both the feather cortex and barbules may be influenced by genetic quality or physiological stress during the development period both of which may determine quality at an individual level.

Tree swallows are small birds (14 cm total length) with long wings and small legs and feet. They are irridescent greenish-blue above and white below on the chin, breast and belly. Tree swallows have a short black beak and dark reddish-brown or brownish-gray feet.

Juvenile tree swallows are similar in appearance to adults, but are brownish rather than greenish blue. They also have a dusky wash across their white chests. One-year-old females look very similar to adults, but have a mixture of brown and irridescent greenish-blue above.

Average length: 14 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

Average mass: 19 g.

Length: 15 cm

Weight: 20 grams

Systems

• Terrestrial
• Freshwater

Tree swallows live in open areas near water, such as fields, marshes, meadows, shorelines, beaver ponds, and wooded swamps. Because tree swallows are cavity nesters, an important habitat requirement is cavities in which to nest. These can be provided by standing dead trees, sapsucker-excavated holes in live trees, under the eaves of buildings,and in artificial nest boxes.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: savanna or grassland ; forest

Aquatic Biomes: lakes and ponds; rivers and streams

Wetlands: marsh ; swamp ; bog

Other Habitat Features: suburban ; agricultural ; riparian

Comments: Open situations near water, including streams, lakes, ponds, marshes and coastal regions (AOU 1983); savanna, pastures, etc. Nests usually near water in a natural tree cavity or abandoned woodpecker hole, less frequently in open woodland away from water. Also nests in bird boxes or in a crevice in a building. Territoriality may limit use of suitable nest sites. Tends to return to same nest site in subsequent years if reproduction successful; first-year breeders return to nest usually within 100 km or less of natal site (Turner and Rose 1989).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Main migration routes include U.S. east coast, Mississippi Basin, along Rockies (see Turner and Rose 1989). Migrates northward early, February-March in most of U.S. (Terres 1980). Large numbers of south-bound migrants pass through Florida in late fall, beginning in late September or October (Smith and Smith 1990). Irregularly rare to locally common migrant in Costa Rica, early September-late October and March-April (Stiles and Skutch 1989).

Tree swallows primarily eat flying insects, though they also eat plant materials (about 20% of their diet). They forage in flight, in open areas above water or ground. They sometimes forage in flocks when insects are abundant. They can also glean insects from the surface of water or vertical surfaces. Swallows feed from dawn until dusk, mainly on flies, beetles and ants, though stoneflies, mayflies, caddisflies, spiders and grasshoppers are also common prey. When weather conditions are bad, tree swallows feed on vegetation, including bulrushes, bayberries, and other plants' seeds.

Animal Foods: insects

Plant Foods: seeds, grains, and nuts; fruit

Primary Diet: carnivore (Insectivore )

Tree Swallows often return to their breeding grounds weeks before local insect abundances reach their peak (McCarty, 1995). To compensate for variations in local food abundance, they appear to selectively forage at ponds where densities of fish are lower, more nutrients and a greater insect emergence (McCarty, 1997).

Comments: Catches flying insects in the air over land or water. Also forages on the ground for beetles, bugs, beach "fleas", and spiders. Occasionally eats some seeds and fruits (e.g., Myrica fruits during inclement weather when insects unavailable, especially in fall in the eastern coastal U.S.) (Place and Stiles 1992).

Tree swallows affect the populations of the animals they eat. They also provide food for their predators. They host a number of body parasites, including blowfly larvae.

Commensal/Parasitic Species:

• blowfly larvae

Tree swallow eggs and nestlings are vulnerable to predation by rat snakes, raccoons, black bears, American kestrels, common grackles, American crows, northern flickers, chipmunks, weasels, deer mice and feral cats. Adults are taken in flight by black-billed magpies and raptors, including sharp-shinned hawks, American kestrels, merlins, peregrine falcons and great horned owls.

Tree swallows respond to predators by mobbing them. Large numbers of tree swallows swarm and dive-bomb the predator while giving alarm calls.

Known Predators:

• rat snakes (Pantherophis obsoletus)
• raccoons (Procyon lotor)
• black bears (Ursus americanus)
• American kestrels (Falco sparverius)
• common grackles (Quiscalus quiscula)
• American crows (Corvus brachyrhynchos)
• northern flickers (Colaptes auratus)
• chipmunks (Tamias)
• weasels (Mustela)
• deer mice (Peromyscus maniculatus)
• feral cats (Felis silvestris)
• black-billed magpies (Pica pica)
• sharp-shinned hawks (Accipiter striatus)
• great horned owls (Bubo virginianus)
• merlins (Falco columbarius)
• peregrine falcons (Falco peregrinus)

Many may congregate where food abundant or in roosts when weather cold. When not breeding, flocks may contain 1000s of individuals.

Tree swallows communicate primarily using sounds and physical displays. Only male tree swallows sing, apparently for the purpose of proclaiming their territory. Both sexes use calls to communicate. At least 14 different tree swallow calls have been identified. The apparent purposes of these calls range from signaling distress, anxiety, pleasure and submission to begging for food and soliciting copulation. Body signals such as crouching and wing-fluttering are used to communicate a variety of messages, including aggression and solicitation of copulation.

Communication Channels: visual ; acoustic

Annual adult tree swallow survival is estimated at 40 to 60%. Estimated average life span of tree swallows is 2.7 years. However, the oldest known tree swallow lived at least 11 years.

Range lifespan

Status: wild: 8 to 11 years.

Average lifespan

Status: wild: 2.7 years.

Average lifespan

Status: wild: 145 months.

Maximum longevity: 12.1 years (wild) Observations: A 25-year study in the wild found that reproductive performance first increased until about 3-5 years of age, possibly due to acquired skills, and then declined, perhaps caused by physiological ageing and influenced by previous reproductive efforts (Robertson and Rendell 2001).

Tree swallows are primarily monogamous. However, polygyny has been documents at low rates in some populations. Breeding pairs form as soon as females arrive at breeding sites in the spring. Extra-pair copulations are common in this species; as many as 50% of nests in a given population may contain young that were not fathered by the resident male.

Mating System: monogamous

Tree swallows breed between May and September, and raise one brood per year. They usually nest solitarily, though they will nest near each other if existing cavities are close together. Nest building takes place in late April or early May. Nests are typically built in cavities in dead or live trees (excavated earlier by woodpeckers or other species) or in hollow stumps over water. However, they can also be found under the eaves of buildings, in steel drums, fire hydrants, holes in the ground or nest boxes. Nests are built almost entirely by the female. They are made of grasses, mosses, rootlets, and aquatic plants, and are lined with feathers from other species of birds. Construction takes from a few days to two weeks.

The female lays 2 to 8 (usually 4 to 7) eggs, at a rate of one per day. The female then incubates the eggs for 11 to 19 (usually 14 to 15) days. The female broods the altricial chicks for the first three days after hatching. Both parents share the responsibility of feeding and finding food for the chicks. Chicks fledge 15 to 25 days after hatching (usually 18 to 22 days), at which time they are good fliers. The parents continue to feed the chicks for at least 3 days after they leave the nest. These chicks will be able to breed the next summer if they are able to establish a nest site.

Breeding interval: Tree swallows breed once per year.

Breeding season: Tree swallows breed between May and September.

Range eggs per season: 2 to 8.

Range time to hatching: 11 to 19 days.

Average time to hatching: 14.5 days.

Range fledging age: 15 to 25 days.

Range time to independence: 3 (low) days.

Average age at sexual or reproductive maturity (female): 1 years.

Average age at sexual or reproductive maturity (male): 1 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Average eggs per season: 5.

Female tree swallows build the nest, incubate the eggs and brood the chicks. Both parents feed the chicks while they are in the nest and for at least three days after they fledge.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female)

Egg dates: late April-late June in south, early May to mid-June in north. Clutch size usually is 4-6. Incubation, typically by fenale, lasts 13-16 days. Altricial young are tended by both sexes, leave nest 16-24 days after hatching (Terres 1980), receive little care after that. Inclement weather and resulting scarcity of food may result in high nestling mortality in some years. In Ontario, productivity was reduced near experimentally acidified lakes (St. Louis and Barlow, 1993, Can. J. Zool. 71:1090-1097). Generally monogamous, but sometimes polygynous if food is superabundant. Nests alone or in loose colony.

All Hirundinids, including Tree Swallows have two distinct visual adaptations to their environments. To view distant objects they rely on forward directional binocular vision, while close objects are perceived through lateral monocular vision (Gill).

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There are 7 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 7
Species: 9
Species With Barcodes: 1

Tree swallows are a relatively common birds. Global populations of tree swallows have increased over the last 25 years to an estimated 20,000,000. Tree swallows readily use nesting boxes, making them a good study species for studies of the effect of pollutant on birds. PCBs and DDE have been found to be present in high levels in adults, eggs, and nestlings. It has also been found that birds in more acidic wetlands produce fewer and smaller young. These observations may suggest a possible long-term problem for tree swallows. A more pressing consideration, however, is the maintenance of dead trees, which provide nest sites for tree swallows and other cavity-dwellers.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5B - Secure

United States

Rounded National Status Rank: N5B,N5N : N5B: Secure - Breeding, N5N: Secure - Nonbreeding

Rounded Global Status Rank: G5 - Secure

Restoration Potential: See Mitchell (1988) for specifications for the construction and placement of nest boxes. See Lumsden (1989) for nest box preference in Ontario.

There are no known adverse effects of tree swallows on humans.

Tree swallows eat many kinds of insects that humans may consider to be pests.

Positive Impacts: controls pest population

Comments: Sometimes placed in the genus IRIDOPROCNE (AOU 1983). See Sheldon and Winkler (1993) for information on intergeneric phylogenetic relationships of Hirundininae based on DNA-DNA hybridization.