Tree swallow

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Tree swallow
Tree swallow at Stroud Preserve.jpg
At Stroud Preserve in West Chester, Pennsylvania, US
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Hirundinidae
Genus: Tachycineta
Species: T. bicolor
Binomial name
Tachycineta bicolor
(Vieillot, 1808)
Tree Swallow-rangemap.gif
Range of T. bicolor       Breeding summer visitor     Migration visitor      Winter visitor

Iridoprocne bicolor

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.

Taxonomy and etymology[edit]

The tree swallow is usually placed in the genus Tachycineta,[2] although it is sometimes placed in the genus Iridoprocne, along with the mangrove swallow, white-rumped swallow, white-winged swallow, and Chilean swallow.[3]

The generally accepted genus name is from Ancient Greek takhukinetos, "moving quickly", and the specific bicolor is Latin and means "two-coloured".[4] The other genus name, Iridoprocne, comes from the Greek iris, meaning rainbow, and Procne, a figure who supposedly turned into a swallow.[5]


This swallow averages 13.5 cm (5.3 in) long and weighs about 20 g (0.71 oz). The bill is tiny. The adult tree swallow has iridescent blue-green upperparts, white underparts, and a very slightly forked tail. The female usually has duller colours than the male, often more greenish than the more bluish male. The juvenile plumage is dull grey-brown above and may have hint of a grey breast band.


Flying in Central New York, US

Being highly social outside of the breeding season, tree swallows may form flocks of several thousand birds near roost sites.[6] Flocks near Vacherie, Louisiana, were estimated to contain well over 1 million birds during December 2009.[7]



The tree swallow nests in pre-existing holes, usually in trees and artificial structures such as pipes and fence posts, and in nestboxes.[2] The nest hole is, on average, 3.4 metres (11 ft) above ground level, although about 45% of them are less than 2 metres (6.6 ft) above the ground.[8] The nest cup itself is made from grass, moss, pine needles, and aquatic plants, and lined with feathers, all of which are collected mostly be the female.[2]

Eggs are laid from early May to mid-June and chicks fledge between mid-June and July. When the eggs are laid is influenced by latitude,[2] age of the female, and wing length of the female.[9] On average, birds in the southern part of the breeding range breed earlier than those in the northern portion.[2] The female's wing length and age are both inversely correlated with the timing of breeding.[9] These observations support the theory that the tree swallow breeds based on food conditions during the laying season. It generally lays when the temperature and the abundance of food (that the female can catch) are good enough for females to start laying eggs.[10] This species is generally socially monogamous, but up to 8% of breeding males are polygynous.[2] It is suggested that this polygyny depends on the conditions during the laying season: better conditions, such as an abundance of food, allow females in polygyny who do not receive help in foraging to lay more eggs.[11]

The tree swallow has high rates of extra-pair paternity, with 38% to 69% of nestlings being a product of extra-pair paternity, and 50% to 87% of broods containing at least one nestling that was the result of an extra-pair copulation.[2] One factor that might contribute to this is that females have control over copulation, making paternity guards ineffective.[12] Extra-pair paternity does not change the level of parental care the male contributes in the tree swallow, contrary to other birds. The tree swallow also differs in terms of the composition of extra-pair fathers; in a study that found the paternity of 35 extra-pair nestlings, it was determined that 25 extra-pair young were from fathers from sites near the nest where the female is, about 3 from sites within 2 kilometres (1.2 mi), and 7 that had fathers that were floaters (those present at breeding grounds that presumably do not breed). In the tree swallow, floating thus helps males in good condition produce more chicks, while allowing males in bad condition to be successful through parental care.[13]

How extra-pair fathers are chosen and why females even breed with other males (because they can control copulation) is controversial. One theory, called the genetic compatibility hypothesis, states that increased offspring fitness results from increased heterozygosity, and thus that female tree swallows would prefer to mate with those that have more different alleles from them. This theory is justified on the basis that young produced from extra-pair mates usually are more heterozygous than within-pair offspring. In additional support of this theory, females are likely able to judge, after copulation, whether or not a male's sperm is of high quality and whether she should allow it to impregnate her.[14] Another theory, called the good genes theory, says that females choose extra-pair males based on if they have good genes that would influence survival and mating success. This is supported on the basis that it is able to explain why some tree swallows do not have any extra-pair young, whereas others do.[12] Although this is true, there is criticism for a lack of phenotypic difference between extra-pair males and pair-bonded males. But, there are results that may be in support of this theory. For example, in a 2007 study, it was found that in increased plumage brightness and increased age in extra-pair males, together, increased the number of extra-pair young.[15]

The tree swallow lays a clutch of two to eight, although usually four to seven,[2] pure white, and translucent at laying, eggs that measure about 19 by 14 centimetres (7.5 by 5.5 in).[16] These eggs are incubated by the female[2] for 11 to 20 days,[16] although most hatch after 14 to 15 days.[2] They hatch slightly asynchronously, with an average of 28 hours between the time of the first and final egg is laid. When a brood hatches asynchronously, a weight hierarchy is established, with nestlings hatched earlier weighing more than those hatched later. This allows for the female to prioritize which chick to give food to in times of food shortage, although this weight difference is less pronounced about 12 days into nesting, suggesting that this brood-reduction only has a significant effect early in the nestling period.[17]


The tree swallow forages 0 to 50 metres (160 ft) above the ground singly or in groups. Its flight is a mix of flapping and gliding. During the breeding season, this is mostly within 4 kilometres (2.5 mi) of the nest site. When it is foraging for nestlings, although, it usually goes up to 200 metres (660 ft) from the nest,[2] mostly staying in sight of it, and forages at a height up to 12 metres (39 ft).[18] Insects are additionally taken from the ground, water, vegetation, and vertical surfaces.[2]

The tree swallow eats mostly insects, with some molluscs, spiders, and fruit. In North America, flies make up about 40% of the diet, with beetles and ants supplementing it. Otherwise, the diet is about 90% flies. The seed and berry food is mainly from the genus Myrica, which is mainly taken in the all four of the Northern Hemisphere seasons except summer. Crustaceans were also found to be important in the wintering diet in a study on Long Island, New York.[2]


  1. ^ BirdLife International (2012). "Tachycineta bicolor". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ a b c d e f g h i j k l m Turner, A. (2017). del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi; Christie, David A.; de Juana, Eduardo, eds. "Tree Swallow (Tachycineta bicolor)". Handbook of the Birds of the World Alive. Barcelona, Spain: Lynx Edicions. Retrieved 10 December 2017. (Subscription required (help)). 
  3. ^ Turner, Angela (2017). del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi; Christie, David A.; de Juana, Eduardo, eds. "White-rumped Swallow (Tachycineta leucorrhoa)". Handbook of the Birds of the World Alive. Lynx Edicions. Retrieved January 14, 2017. (Subscription required (help)). 
  4. ^ Jobling, James A (2010). The Helm Dictionary of Scientific Bird Names. London: Christopher Helm. pp. 72, 377. ISBN 978-1-4081-2501-4. 
  5. ^ Coues, Elliott (1882). The Coues Check List of North American Birds. Boston: Estes and Lauriat. p. 42. 
  6. ^ Animal Diversity Web: Tree Swallow
  7. ^ Ed Cullen. Millions of tree swallows swirl down in Vacherie. AP Louisiana News. Posted 19 December 2009.
  8. ^ Rendell, Wallace B.; Robertson, Raleigh J. (1989). "Nest-site characteristics, reproductive success and cavity availability for tree swallows breeding in natural cavities". The Condor. 91 (4): 875. doi:10.2307/1368072. ISSN 0010-5422. 
  9. ^ a b Winkler, David W.; Allen, Paul E. (1996). "The seasonal decline in tree swallow clutch size: physiological constraint or strategic adjustment?". Ecology. 77 (3): 922–932. doi:10.2307/2265512. ISSN 0012-9658. 
  10. ^ Nooker, Jacqueline K.; Dunn, Peter O.; Whittingham, Linda A. (2005). "Effects of food abundance, weather, and female condition on reproduction in tree swallows (Tachycineta bicolor)". The Auk. 122 (4): 1225. doi:10.1642/0004-8038(2005)122[1225:EOFAWA]2.0.CO;2. ISSN 0004-8038. 
  11. ^ Dunn, Peter O.; Hannon, Susan J. (1992). "Effects of food abundance and male parental care on reproductive success and monogamy in tree swallows". The Auk. 109 (3): 488–499. ISSN 0004-8038. 
  12. ^ a b Lifjeld, Jan T.; Dunn, Peter O.; Robertson, Raleigh J.; Boag, Peter T. (1993). "Extra-pair paternity in monogamous tree swallows". Animal Behaviour. 45 (2): 213–229. doi:10.1006/anbe.1993.1028. ISSN 0003-3472. 
  13. ^ Kempenaers, Bart; Everding, Susie; Bishop, Cheryl; Boag, Peter; Robertson, Raleigh J. (2001). "Extra-pair paternity and the reproductive role of male floaters in the tree swallow (Tachycineta bicolor)". Behavioral Ecology and Sociobiology. 49 (4): 251–259. doi:10.1007/s002650000305. ISSN 0340-5443. 
  14. ^ Stapleton, Mary K.; Kleven, Oddmund; Lifjeld, Jan T.; Robertson, Raleigh J. (2007). "Female tree swallows (Tachycineta bicolor) increase offspring heterozygosity through extrapair mating". Behavioral Ecology and Sociobiology. 61 (11): 1725–1733. doi:10.1007/s00265-007-0404-4. ISSN 0340-5443. 
  15. ^ Bitton, Pierre-Paul; O'Brien, Erin L.; Dawson, Russell D. (2007). "Plumage brightness and age predict extrapair fertilization success of male tree swallows, Tachycineta bicolor". Animal Behaviour. 74 (6): 1777–1784. doi:10.1016/j.anbehav.2007.03.018. ISSN 0003-3472. 
  16. ^ a b Hauber, Mark E. (1 August 2014). The Book of Eggs: A Life-Size Guide to the Eggs of Six Hundred of the World's Bird Species. Chicago: University of Chicago Press. p. 448. ISBN 978-0-226-05781-1. 
  17. ^ Clotfelter, Ethan D.; Whittingham, Linda A.; Dunn, Peter O. (2000). "Laying order, hatching asynchrony and nestling body mass in tree swallows Tachycineta bicolor". Journal of Avian Biology. 31 (3): 329–334. doi:10.1034/j.1600-048X.2000.310308.x. ISSN 0908-8857. 
  18. ^ McCarty, John P.; Winkler, David W. (1999). "Foraging ecology and diet selectivity of tree swallows feeding nestlings". The Condor. 101 (2): 246–254. doi:10.2307/1369987. ISSN 0010-5422. 

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