Barn Swallow

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Barn Swallow
European subspecies, H. r. rustica in Denmark
European subspecies,
H. r. rustica in Denmark
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Hirundinidae
Genus: Hirundo
Species: H. rustica
Binomial name
Hirundo rustica
Linnaeus, 1758
      Breeding range;       Resident year-round;       Non-breeding range
      Breeding range;       Resident year-round;       Non-breeding range
Synonyms

Hirundo erythrogaster

The Barn Swallow (Hirundo rustica) is the most widespread species of swallow in the world.[2] A distinctive passerine bird with blue upperparts, a long, deeply forked tail and curved, pointed wings, it is found in Europe, Asia, Africa and the Americas.[2] In Anglophone Europe it is just called the Swallow; in Northern Europe it is the only common species called a "swallow" rather than a "martin".[3]

There are six subspecies of Barn Swallow, which breed across the Northern Hemisphere. Four are strongly migratory, and their wintering grounds cover much of the Southern Hemisphere as far south as central Argentina, the Cape Province of South Africa, and northern Australia.[2] Its huge range means that the Barn Swallow is not endangered, although there may be local population declines due to specific threats, such as the construction of an international airport near Durban.[4]

The Barn Swallow is a bird of open country which normally uses man-made structures to breed and consequently has spread with human expansion. It builds a cup nest from mud pellets in barns or similar structures and feeds on insects caught in flight.[5]

This species lives in close association with humans, and its insect-eating habits mean that it is tolerated by man; this acceptance was reinforced in the past by superstitions regarding the bird and its nest. There are frequent cultural references to the Barn Swallow in literary and religious works due to both its living in close proximity to humans and its conspicuous annual migration.[6] The Barn Swallow is the national bird of Estonia.

Contents

[edit] Description

H. r. rustica in England
H. r. rustica in England

The adult male Barn Swallow of the nominate subspecies H. r. rustica is 17–19 centimetres (6.7–7.5 in) long including 2–7 centimetres (0.8–2.8 in) of elongated outer tail feathers. It has a wingspan of 32–34.5 centimetres (12.6–13.6 in) and weighs 16–22 grams (0.56–0.78 oz). It has steel blue upperparts and a rufous forehead, chin and throat, which are separated from the off-white underparts by a broad dark blue breast band. The outer tail feathers are elongated, giving the distinctive deeply-forked "swallow tail." There is a line of white spots across the outer end of the upper tail.[5]

The female is similar in appearance to the male, but the tail streamers are shorter, the blue of the upperparts and breast band is less glossy, and the underparts more pale. The juvenile is browner and has a paler rufous face and whiter underparts. It also lacks the long tail streamers of the adult.[2]

The song of the Barn Swallow is a cheerful warble, often ending with su-seer with the second note higher than the first but falling in pitch. Calls include witt or witt-witt and a loud splee-plink when excited.[5] The alarm calls include a sharp siflitt for predators like cats and a flitt-flitt for birds of prey like the Hobby.[7] This species is fairly quiet on the wintering grounds.[8]

The distinctive combination of a red face and blue breast band render the adult Barn Swallow easy to distinguish from the African Hirundo species and from the Welcome Swallow (Hirundo neoxena) with which its range overlaps in Australasia.[2] In Africa the short tail streamers of the juvenile Barn Swallow invite confusion with juvenile Red-chested Swallow (Hirundo lucida), but the latter has a narrower breast band and more white in the tail.[9]

[edit] Taxonomy

The Barn Swallow was described by Linnaeus in his Systema Naturae in 1758 as Hirundo rustica, characterised as H. rectricibus, exceptis duabus intermediis, macula alba notatîs.[10] Hirundo is the Latin word for "swallow"; rusticus means "of the country."[11] This species is the only one of that genus to have a range extending into the Americas, with the majority of Hirundo species being native to Africa. This genus of blue-backed swallows is sometimes called the "barn swallows."[2]>[12]

There are few taxonomic problems within the genus, but the Red-chested Swallow – a resident of West Africa, the Congo basin and Ethiopia – was formerly treated as a subspecies of Barn Swallow. The Red-chested Swallow is slightly smaller than its migratory relative, has a narrower blue breast-band, and the adult has shorter tail streamers. In flight, it also looks paler underneath than Barn Swallow.[9]

H. r. rustica in Poland
H. r. rustica in Poland

[edit] Subspecies

Six subspecies of Barn Swallow are generally recognized. In eastern Asia, a number of additional or alternative forms have been proposed, including saturata by Robert Ridgway in 1883,[13] kamtschatica by Benedykt Dybowski in 1883,[14] and mandschurica by Wilhelm Meise in 1934.[13] Given the uncertainties over the validity of these forms,[14] this article follows the treatment of Turner and Rose.[2]

  • H. r. rustica, the nominate European subspecies, breeds in Europe and Asia, as far north as the Arctic Circle, south to North Africa, the Middle East and Sikkim, and east to the Yenisei River. It migrates on a broad front to winter in Africa, Arabia, and the Indian subcontinent.[2] The Barn Swallows wintering in southern Africa are from across Eurasia to at least 91°E,[15] and have been recorded as covering up to 11,660 kilometres (7,250 miles) on their annual migration.[16]
  • H. r. transitiva was described by Ernst Hartert in 1910.[13] It breeds in the Middle East from southern Turkey to Israel and is partially resident, though some birds winter in East Africa. It has orange red underparts and a broken breast band.[2]
H. r. gutturalis in Japan
H. r. gutturalis in Japan
  • H. r. gutturalis, described by Giovanni Antonio Scopoli in 1786,[13] has whitish underparts and a broken breast band. It breeds from the eastern Himalayas to Japan and Korea. It winters across tropical Asia from India and Sri Lanka east to Indonesia and New Guinea. Increasing numbers are wintering in Australia. It hybridises with H. r. tytleri in the Amur River area. It is thought that the two eastern Asia forms were once geographically separate, but the nest sites provided by expanding human habitation allowed the ranges to overlap.[2] H. r. gutturalis is a vagrant to Alaska and Washington,[18] but is easily distinguished from the North American breeding subspecies, H. r. erythrogaster, by the latter's reddish underparts.[2]
H. r. erythrogaster in Canada
H. r. erythrogaster in Canada
  • The North American subspecies H. r. erythrogaster, described by Pieter Boddaert in 1783,[13] differs from the European subspecies in having redder underparts and a narrower, often incomplete, blue breast band. It breeds throughout North America, from Alaska to southern Mexico, and migrates to the Lesser Antilles, Costa Rica, Panama and South America to winter.[8] A few may winter in the southernmost parts of the breeding range. This subspecies funnels through Central America on a narrow front and is therefore abundant on passage in the lowlands of both coasts.[19]

Unexpectedly, DNA analyses show that Barn Swallows from North America colonised the Baikal region of Siberia, a dispersal direction opposite to that for most changes in distribution between North America and Eurasia.[20]

[edit] Behaviour

[edit] Habitat and range

The preferred habitat of the Barn Swallow is open country with low vegetation, such as pasture, meadows and farmland, preferably with nearby water. This swallow avoids heavily wooded or precipitous areas and densely built-up locations. The presence of accessible open structures such as barns, stables, or culverts to provide nesting sites, and exposed locations such as wires, roof ridges or bare branches for perching, are also important in the bird's selection of its breeding range.[5]

In Kolkata, India
In Kolkata, India

It breeds in the Northern Hemisphere from sea level to typically 2,700 metres (8,900 ft),[21] but to 3,000 metres (9,800 ft) in the Caucasus[5] and North America,[22] and it is absent only from deserts and the cold northernmost parts of the continents. Over much of its range, it avoids towns, and in Europe is replaced in urban areas by the House Martin. However, in Honshū, the Barn Swallow is a more urban bird, with the Red-rumped Swallow (Cecropis daurica) replacing it as the rural species.[2]

In winter, the Barn Swallow is cosmopolitan in its choice of habitat, avoiding only dense forests and deserts.[23] It is most common in open, low vegetation habitats, such as savanna and ranch land, and in Venezuela, South Africa and Trinidad and Tobago it is described as being particularly attracted to burnt or harvested sugarcane fields and the waste from the cane.[8][24][25] Individual birds tend to return to the same wintering locality each year[26] and congregate from a large area to roost in reed beds.[24] The Barn Swallow has been recorded as breeding in the more temperate parts of its winter range, such as the mountains of Thailand and in central Argentina.[27][2]

As would be expected for a long-distance migrant, this bird has occurred as a vagrant to such distant areas as Hawaii, Bermuda, Greenland, Tristan da Cunha and the Falkland Islands.[2]

[edit] Feeding

In flight
In flight

The Barn Swallow is similar in its habits to other aerial insectivores, including other swallow species and the unrelated swifts. It is not a particularly fast flier, with a speed estimated at about 11 m/s (36 ft/s) and a wing beat rate of approximately 7–9 times each second,[28] but it has the manoeuvrability necessary to feed on flying insects while airborne. It is often seen flying relatively low in open or semi-open areas.

It typically feeds 7–8 metres (23–26 ft) above shallow water or the ground, often following animals, humans or farm machinery to catch disturbed insects, but it will occasionally pick prey items from the water surface, walls and plants. In the breeding areas, large flies make up around 70% of the diet, with aphids also a significant component. However, in Europe, the Barn Swallow consumes fewer aphids than the House or Sand Martins.[5] On the wintering grounds, Hymenoptera, especially flying ants, are important food items. When egg-laying, Barn Swallows hunt in pairs, but will form often large flocks otherwise.[2]

Isotope studies have shown that wintering populations may utilise different feeding habitats, with British breeders feeding mostly over grassland, whereas Swiss birds utilised woodland more.[29] Another study showed that a single population breeding in Denmark actually wintered in two separate and different areas.[30]

The Barn Swallow drinks by skimming low over lakes or rivers and scooping up water with its open mouth.[22] This bird bathes in a similar fashion, dipping into the water for an instant while in flight.[26]

Swallows gather in communal roosts after breeding, sometimes thousands strong. Reed beds are regularly favoured, with the birds swirling en masse before swooping low over the reeds.[7] Reed beds are an important source of food prior to and whilst on migration; although the Barn Swallow is a diurnal migrant which can feed on the wing whilst it travels low over ground or water, the reed beds enable fat deposits to be established or replenished.[31]

[edit] Breeding

The male Barn Swallow returns to the breeding grounds before the females and selects a nest site, which is then advertised to females with a circling flight and song. The breeding success of the male is related to the length of the tail streamers, with longer streamers being more attractive to the female.[5][32] Males with longer tail feathers are generally longer-lived and more disease resistant, females thus gaining an indirect fitness benefit from this form of selection, since longer tail feathers indicate a genetically stronger individual which will produce offspring with enhanced vitality.[33]

Chicks and eggs in a nest with horse hair lining
Chicks and eggs in a nest with horse hair lining

Males with long streamers also have larger white tail spots, and since feather-eating bird lice prefer white feathers, large white tail spots without parasite damage again demonstrate breeding quality; there is a positive association between spot size and the number of offspring produced each season.[34]

Both sexes defend the nest, but the male is particularly aggressive and territorial.[2] Once established, pairs stay together to breed for life, but extra-pair copulation is common, making this species genetically polygamous, despite being socially monogamous.[35] Males guard females actively to avoid being cuckolded.[36] Males may use deceptive alarm calls to disrupt extrapair copulation attempts toward their mates.[37]

As its name implies, the Barn Swallow typically nests inside accessible buildings such as barns and stables, or under bridges and wharves. The neat cup-shaped nest is placed on a beam or against a suitable vertical projection. It is constructed by both sexes, although more often by the female, with mud pellets collected in their beaks and lined with grasses, feathers or other soft materials.[2] Barn Swallows may nest colonially where sufficient high-quality nest sites are available, and within a colony, each pair defends a territory around the nest which, for the European subspecies, is four to eight square metres (45 to 90 square feet) in size. Colony size tends to be larger in North America.[22]

Older chicks in nest
Older chicks in nest

In North America at least, Barn Swallows frequently engage in a mutualist relationship with Ospreys. Barn Swallows will build their nest below an Osprey nest, receiving protection from other birds of prey which are repelled by the exclusively fish-eating Ospreys. The Ospreys are alerted to the presence of these predators by the alarm calls of the swallows.[22]

Before man-made sites became common, the Barn Swallow nested on cliff faces or in caves, but this is now rare. The female lays two to seven, but typically four or five, reddish-spotted white eggs. The eggs are 20 x 14 millimetres (0.6 x 0.8 in) in size, and weigh 1.9 grammes (0.07 oz), of which 5 percent is shell. In Europe, the female does almost all the incubation, but in North America the male may incubate up to 25% of the time. The incubation period is normally 14–19 days, with another 18–23 days before the altricial chicks fledge. The fledged young stay with, and are fed by, the parents for about a week after leaving the nest. Occasionally, first-year birds from the first brood will assist in feeding the second brood.[2]

Fledged young waiting to be fed
Fledged young waiting to be fed

The Barn Swallow will mob intruders such as cats or accipiters that venture too close to their nest, often flying very close to the threat.[33] Adult Barn Swallows have few predators, but some are taken by accipiters, falcons, and owls. Brood parasitism by cowbirds in North America or cuckoos in Eurasia is rare.[22][5]

There are normally two broods, with the original nest being reused for the second brood and being repaired and reused in subsequent years. Hatching success is 90% and the fledging survival rate is 70–90%. Average mortality is 70–80% in the first year and 40–70% for the adult. Although the record age is more than 11 years, most survive less than four years.[2]

The Barn Swallow has been recorded as hybridising with the Cliff Swallow (Petrochelidon pyrrhonota) and the Cave Swallow (P. fulva) in North America, and the House Martin (Delichon urbicum) in Eurasia, the cross with the latter being one of the most common passerine hybrids.[33]

[edit] Status

The Barn Swallow has an enormous range, with an estimated global extent of 10 million square kilometres (4 million square miles) and a population of 190 million individuals. Although global population trends have not been quantified, the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (that is, declining more than 30 percent in ten years or three generations). For these reasons, the species is evaluated as "least concern" on the 2007 IUCN Red List,[1] and has no special status under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which regulates international trade in specimens of wild animals and plants.[22]

This is a species which has greatly benefited historically from forest clearance, which has created the open habitats it prefers, and from human habitation, which have given it an abundance of safe man-made nest sites. There have been local declines due to the use of DDT in Israel in the 1950s, competition for nest sites with House Sparrows in the US in the 19th century, and an ongoing gradual decline in numbers in parts of Europe and Asia due to agricultural intensification, reducing the availability of insect food. However, there has been an increase in the population in North America during the 20th century with the greater availability of nesting sites and subsequent range expansion, including the colonisation of northern Alberta.[2]

A specific threat to wintering birds from the European populations is the transformation by the South African government of a light aircraft runway near Durban into an international airport for the 2010 FIFA World Cup. The roughly 250 metres (275 yards) square Mount Moreland reed bed is a night roost for more than three million Barn Swallows, which represent one percent of the global population and eight percent of the European breeding population. The reed bed lies on the flight path of aircraft using the proposed La Mercy airport, and there were fears that it would be cleared because the birds could threaten aircraft safety.[4][21] However, following detailed evaluation, advanced radar technology will be installed to enable planes using the airport to be warned of bird movements and, if necessary, take appropriate measures to avoid the flocks.[24]

[edit] Relationship with humans

A male
A male

The Barn Swallow is an attractive bird which feeds on flying insects and has therefore been tolerated by humans when it shares their buildings for nesting. As one of the earlier migrants, this conspicuous species is also seen as an early sign of summer's approach.[38]

In the Old World, the Barn Swallow appears to have used man-made structures and bridges since time immemorial.[39] An early reference is in Virgil's Georgics (29 BC) ...garrula quam tignis nidum suspendat hirundo (...the twittering swallow hangs its nest from the rafters).[40]

It is believed that the Barn Swallow began attaching its nest to Native American habitations in the early 19th century, and the subsequent spread of settlement across North America is thought to have resulted in a dramatic population expansion of the species across the continent.[20]

[edit] In literature

Many literary references are based on the Barn Swallow's northward migration as a symbol of spring or summer. The proverb about the necessity for more than one piece of evidence goes back at least to Aristotle's Nicomachean Ethics: "For as one swallow or one day does not make a spring, so one day or a short time does not make a fortunate or happy man."[38]

The Barn Swallow symbolizes the coming of spring and thus love in the Pervigilium Veneris, a late Latin poem. In "The Waste Land," T. S. Eliot quoted the line "Quando fiam uti chelidon [ut tacere desinam]?" ("When will I be like the swallow, so that I can stop being silent?") This refers to a version of the myth of Philomela in which she turns into a Nightingale and her sister Procne into a Swallow; in less familiar versions, the two species are reversed.[41] On the other hand, an image of the assembly of Swallows for their southward migration concludes John Keats's ode "To Autumn."

There are mentions of the Barn Swallow in the Bible, although it seems likely that it is confused with the swifts in many translations,[42] or possibly other hirundine species which breed in Israel.[7] However, "Yea, the sparrow hath found her a house, And the swallow a nest for herself, where she may lay her young" from Psalms 84:3 likely applies to the Barn Swallow.[42]

The swallow is also notably cited in several of William Shakespeare's plays for the swiftness of its flight; for example: "True hope is swift, and flies with swallow's wings..." from Act 5 of Richard III, and "I have horse will follow where the game Makes way, and run like swallows o'er the plain." from the second act of Titus Andronicus. Shakespeare also references the annual migration of the species poetically in The Winter's Tale, Act 4: "Daffodils, That come before the swallow dares, and take The winds of March with beauty; violets dim,...".

[edit] In culture

On an Estonian 500 Kroon bill
On an Estonian 500 Kroon bill

Gilbert White studied the Barn Swallow in detail in his pioneering work The Natural History of Selborne, but even this careful observer was uncertain whether it migrated or hibernated in winter.[43] Elsewhere, its long journeys have been well-observed, and a swallow tattoo is popular amongst nautical men as a symbol of a safe return; the tradition was that a mariner had a tattoo of this fellow wanderer after sailing 5,000 nautical miles (9,260 km, 5,755 statute miles). A second swallow would be added after 10,000 nautical miles (18,520 km, 11,510 statute miles) at sea.[44]

In the past, the tolerance for this beneficial insectivore was reinforced by superstitions regarding damage to the Barn Swallow's nest. Such an act might lead to cows giving bloody milk, or no milk at all, or to hens ceasing to lay.[6] This may be a factor in the longevity of swallows' nests. Survival, with suitable annual refurbishment, for 10–15 years is regular, and one nest was reported to have been occupied for 48 years.[6]


It is depicted as the Martlet, Merlette or Merlot in heraldry, where it represents younger sons who have no lands. It is also represented as lacking feet as this was a common belief at the time.[45] As a result of a campaign by ornithologists, the Barn Swallow has been the national bird of Estonia since 23 June 1960.[46][47]

[edit] References

  1. ^ a b BirdLife International Species factsheet: Hirundo rustica. BirdLife International. Retrieved on 2007-11-15.
  2. ^ a b c d e f g h i j k l m n o p q r s t u Turner, Angela K; Rose, Chris (1989). Swallows & martins: an identification guide and handbook. Boston: Houghton Mifflin. ISBN 0-395-51174-7.  p164–169
  3. ^ See Gill, Frank, and Wright, Minturn, Birds of the World: Recommended English Names (Princeton 2006), ISBN 978-0691128276
  4. ^ a b "World Cup airport 'threatens swallow population'", The Guardian, 16 November 2006. Retrieved on 2007-11-27. 
  5. ^ a b c d e f g h Snow, David; Perrins, Christopher M (editors) (1998). The Birds of the Western Palearctic concise edition (2 volumes). Oxford: Oxford University Press. ISBN 0-19-854099-X.  p1061–1064
  6. ^ a b c Cocker, Mark; Mabey, Richard (2005). Birds Britannica. London: Chatto & Windus. ISBN 0-7011-6907-9. 
  7. ^ a b c d Mullarney, Killian; Svensson, Lars; Zetterstrom, Dan; Grant, Peter (1999). Collins Bird Guide. London: HarperCollins. ISBN 0-00-219728-6.  p242
  8. ^ a b c Hilty, Steven L (2003). Birds of Venezuela. London: Christopher Helm. ISBN 0-7136-6418-5.  p691
  9. ^ a b Barlow, Clive; Wacher, Tim; Disley, Tony (1997). A Field Guide to birds of The Gambia and Senegal. Robertsbridge: Pica Press. ISBN 1-873403-32-1.  p279
  10. ^ (Latin) Linnaeus, C (1758). Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.. Holmiae. (Laurentii Salvii)., p. 191. 
  11. ^ uk.rec.birdwatching, scientific bird names explained. Retrieved 28 November 2007
  12. ^ Gill, Frank, and Wright, Minturn (2006), Birds of the World: Recommended English Names Princeton: Princeton, ISBN 978-0691128276
  13. ^ a b c d e f Dickinson, Edward C.; Eck, Siegfried; Christopher M. Milensky (2002). "Systematic notes on Asian birds. 31. Eastern races of the barn swallow Hirundo rustica Linnaeus, 1758". Zoologische Verhandelingen, Leiden 340: 201–203. ISSN 0024-1652. 
  14. ^ a b Dickinson, Edward C.; René Dekker (2001). "Systematic notes on Asian birds. 13. A preliminary review of the Hirundinidae". Zoologische Verhandelingen, Leiden 335: 127–144. ISSN 0024-1652. 
  15. ^ European Swallow Hirundo rustica. SAFRING results. Avian Demography Unit, Department of Statistical Sciences, University of Cape Town. Retrieved on 2007-12-01.
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  19. ^ Stiles, Gary; Skutch, Alexander (2003). A guide to the Birds of Costa Rica. Ithaca, New York: Cornell University Press. ISBN 0-8014-2287-6.  p343
  20. ^ a b Williams, Nigel (April 2006). "Swallows track human moves". Current Biology 16 (7): R231. doi:10.1016/j.cub.2006.03.031. 
  21. ^ a b BirdLife International Species factsheet: Hirundo rustica. BirdLife International. Retrieved on 2007-12-06.
  22. ^ a b c d e f Dewey, Tanya; Roth, Chava (2002). Hirundo rustica. Animal Diversity Web. University of Michigan Museum of Zoology. Retrieved on 2007-11-19.
  23. ^ Sinclair, Ian; Hockey, Phil; Tarboton, Warwick (2002). SASOL Birds of Southern Africa. Cape Town: Struik. ISBN 1-86872-721-1.  p294
  24. ^ a b c Froneman, Albert; Bortle, Jon; Merritt, Ron. "Draft swallow monitoring and bird aircraft interaction" (PDF), Environmental Impact Assessment Report, Dube TradePort Environmental Impact Assessment Information Center, April 2007. Retrieved on 2007-11-29. 
  25. ^ ffrench, Richard (1991). A Guide to the Birds of Trinidad and Tobago, 2nd edition, Ithaca, New York: Comstock Publishing. ISBN 0-8014-9792-2.  p315–6
  26. ^ a b Burton, Robert (1985). Bird behaviour. London: Granada. ISBN 0-24-612440-7. 
  27. ^ Lekagul, Boonsong; Round, Philip (1991). A Guide to the Birds of Thailand. Bangkok: Saha Karn Baet. ISBN 974-85673-6-2.  p234
  28. ^ Park, Kirsty; Rosén, Mikael; Hedenström, Anders (August 2001). "Kinematics of the barn swallow (Hirundo rustica) over a wide range of speeds in a wind tunnel". The Journal of Experimental Biology 204 (15): 2741–2750. 
  29. ^ Evans, K. L.; Wadron, S.; Bradbury, R. B. (2003). "Segregation in the African wintering grounds of English and Swiss Barn Swallows Hirundo rustica: a stable isotope study". Bird Study 50: 294–299. 
  30. ^ Møller, Anders Pape; Hobson, K. A. (2004). "Heterogeneity in stable isotope profiles predicts coexistence of populations of Barn Swallows Hirundo rustica differing in morphology and reproductive performance". Proceedings of the Royal Society of London 271: 1355–1362. doi:10.1098/rspb.2003.2565. 
  31. ^ Pilastro, Andrea (December 1998). The EURING Swallow Project in Italy. Euring Newsletter, Volume 2. Retrieved on 2007-12-01.
  32. ^ Saino, Nicola; Romano, Maria; Sacchi; Roberto; Ninni, Paola; Galeotti, Paolo; Møller, Anders Pape (September 2003). "Do male barn swallows (Hirundo rustica) experience a trade-off between the expression of multiple sexual signals?". Behavioral Ecology and Sociobiology 54 (5): 465–471. doi:10.1007/s00265-003-0642-z. 
  33. ^ a b c Møller, Anders Pape (1994). Sexual Selection and the Barn Swallow. Oxford: Oxford University Press, p. 245. ISBN 0-19-854028-0. 
  34. ^ Kose, Mati; Mänd, Raivo: Møller, Anders Pape (December 1999). "Sexual selection for white tail spots in the barn swallow in relation to habitat choice by feather lice". Animal Behaviour 58 (6): 1201–1205. doi:10.1006/anbe.1999.1249. 
  35. ^ Møller, Anders Pape; Tegelstrom, Håkan (November 1997). "Extra-pair paternity and tail ornamentation in the barn swallow". Behavioral Ecology and Sociobiology 41 (5): 353–360. doi:10.1007/s002650050395. 
  36. ^ Møller, Anders Pape (October 1985). "Mixed reproductive strategy and mate guarding in a semi-colonial passerine, the swallow Hirundo rustica". Behavioral Ecology and Sociobiology 17 (4): 401–408. doi:10.1007/BF00293220. 
  37. ^ Møller, Anders Pape (1990). "Deceptive use of alarm calls by male swallows, Hirundo rustica: a new paternity guard". Behavioral Ecology 1 (1): 1–6. 
  38. ^ a b Welldon, James Edward Cowell (translator) [1897] (1987). "Book 1, chapter 6", The Nicomachean Ethics of Aristotle. Buffalo: Prometheus. ISBN 0-87975-378-1. 
  39. ^ Turner, Angela K (2006). The Barn Swallow. London: T. & A. D. Poyser. ISBN 0-7136-6558-0. 
  40. ^ (Latin) Virgil, The Georgics Text Book IV line 307. Retrieved 28 November 2007
  41. ^ Nims, John Frederick (1981). The Harper Anthology of Poetry. New York: Harper and Row. ISBN 0-06-044846-6. 
  42. ^ a b "Swallow", International Standard Bible Encyclopedia, Bible History Online. Retrieved on 2007-11-18. 
  43. ^ White, Gilbert [1789] (1887). The Natural History and Antiquities of Selborne. London: Cassell & Company, pp. 38–39. OCLC 3423785. 
  44. ^ Hardtack and marlinspikes – life and work aboard ship (PDF). Sailors' tattoos post-visit activity, teachers' handout. Maritime Museum of British Columbia. Retrieved on 2007-12-01.
  45. ^ Cooper, JC (1992). Symbolic and Mythological Animals. London: Aquarian Press, 218-19. ISBN 1-85538-118-4. 
  46. ^ The State - Structure and Symbols. Estonia. Estonian Embassy in London. Retrieved on 2007-11-27.
  47. ^ National symbols of Estonia. The Estonia Institute. Retrieved on 2007-11-27.

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