Tachycineta bicolor

Geographic Range

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 nearctic
  • native native
• neotropical neotropical
  • native native

Habitat

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 temperate
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest

• Aquatic Biomes
• lakes and ponds
• rivers and streams

• Wetlands
• marsh marsh
• swamp swamp
• bog bog

• Other Habitat Features
• suburban suburban
• agricultural agricultural
• riparian riparian

Physical Description

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.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

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 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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

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 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

Lifespan/Longevity

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.

Behavior

Tree swallows are highly social and may form flocks of several thousand birds at nighttime roosts outside of the breeding season. However, they are strongly territorial during the breeding season. Both sexes defend an area around their nest, usually a 10 to 15 m radius, against conspecifics and other nest site competitors. Competition for nest sites is thought to be the underlying motive behind much of tree swallow behavior, including sexually selective infanticide, frequent copulation, and strong aggressive responses to nest site competitors.

Tree swallows are fully migratory. They migrate during the day, often in loose flocks, and roost together in large groups at night.

As their name suggests, tree swallows spend little time on the ground, preferring instead to perch. They spend much of their time in flight and tend to glide more than any other species of swallows . In order to bathe, swallows swoop down over water. They lightly brush the water and then begin to fly upwards, shaking the water off. They also bathe by preening extensively during rainfall, using it as a shower.

• Key Behaviors
• arboreal arboreal
• flies
• diurnal diurnal
• motile motile
• migratory migratory
• territorial territorial
• social social

Home Range

The size of tree swallow home ranges changes throughout the year. Before eggs are laid, tree swallows may travel up to 60 km to forage. However, during the incubation and nestling stages, tree swallows probably stay within about 5 km of the nest site.

Communication and Perception

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 visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• insects

• Plant Foods
• seeds, grains, and nuts
• fruit

Predation

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.

Ecosystem Roles

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.

Economic Importance for Humans: Positive

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

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

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

Conservation Status

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.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Kari Kirschbaum (author, editor), Animal Diversity Web.

Jennifer Roof (author), University of Michigan-Ann Arbor, Marie S. Harris (author), University of Michigan-Ann Arbor.

References

Harrison, H. 1975. A field guide to the birds' nests: United States east of the Mississippi River . New York: Houghton Mifflin, Peterson Field Guide Series.

Robertson, R., B. Stutchbury, R. Cohen. 1992. Tree Swallow ( Tachycineta bicolor ). Pp. 1-28 in The Birds of North America , Vol. 11. Philadelphia, PA: The Academy of Natural Sciences; Washington, DC: The American Ornithologists' Union.