Tree Swallow

Tachycineta bicolor

Summary 4

The Tree Swallow (Tachycineta bicolor) is a migratory passerine bird that breeds in North America and winters in Mexico, Central America and the Caribbean. It is a very rare vagrant to western Europe.

Color of external features 5

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.

Conservation status 6

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

Habitat 7

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

Sources and Credits

  1. (c) Greg's Always Catchin' Up, some rights reserved (CC BY-NC-SA), https://www.flickr.com/photos/stitch1958/2507091465/
  2. (c) Rick Leche, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/64649343@N00/435466650
  3. (c) Steve Thompson, some rights reserved (CC BY-NC-SA), https://www.flickr.com/photos/srdt6458/32938783264/
  4. Adapted by Amanda Carrillo-Perez from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Tachycineta_bicolor
  5. (c) Unknown, some rights reserved (CC BY-NC), http://eol.org/data_objects/17433849
  6. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31425617
  7. (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31425607

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