Editing Barn swallow (section)

=== Breeding ===

[[File:Hirundo rustica MHNT.jpg |Swallow eggs, hatched|thumb|alt=See caption]]

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.<ref name=BWP/> Plumage may be used to advertise: in some populations, like in the subspecies ''H. r. gutturalis'', darker ventral plumage in males is associated with higher breeding success. In other populations,<ref name="LiuScordato2018">{{cite journal|last1=Liu|first1=Yu|last2=Scordato|first2=Elizabeth S. C.|last3=Safran|first3=Rebecca|last4=Evans|first4=Matthew|s2cid=19235964|title=Ventral colour, not tail streamer length, is associated with seasonal reproductive performance in a Chinese population of barn swallows (''Hirundo rustica gutturalis'')|journal=Journal of Ornithology|volume=159|issue=3|year=2018|pages=675–685|issn=2193-7192|doi=10.1007/s10336-018-1555-y|bibcode=2018JOrni.159..675L }}</ref> the breeding success of the male is related to the length of the tail streamers, with longer streamers being more attractive to the female.<ref name=BWP/><ref name = Saino>{{cite journal |last=Saino |first=Nicola|author2=Romano, Maria|author3=Sacchi|author4=Roberto|author5=Ninni, Paola|author6=Galeotti, Paolo|author7= Møller, Anders Pape |s2cid=35334066|date=September 2003 |title=Do male barn swallows (''Hirundo rustica'') experience a trade-off between the expression of multiple sexual signals? |journal=Behavioral Ecology and Sociobiology |volume=54 |issue=5 |pages=465–471 |doi=10.1007/s00265-003-0642-z|bibcode=2003BEcoS..54..465S }}</ref> 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.<ref name= Moller/> Males in northern Europe have longer tails than those further south, whereas in Spain the male's tail streamers are only 5% longer than the female's; in Finland, the difference is 20%. In Denmark, the average male tail length increased by 9% between 1984 and 2004, but it is possible that climatic changes may lead in the future to shorter tails if summers become hot and dry.<ref name= BB102/>

[[File:Hirundo rustica 14105.JPG|Older chicks in nest|alt=see caption|thumb|left]]

Males with long streamers also have larger white tail spots, and since feather-eating [[chewing louse|bird lice]] prefer white feathers, large white tail spots without [[Parasitism|parasite]] damage again demonstrate breeding quality; a positive association exists between spot size and the number of offspring produced each season.<ref name= Kose>{{cite journal |last=Kose |first=Mati |author2=Mänd, Raivo|author3=Møller, Anders Pape |s2cid=24583746 |date=December 1999 |title=Sexual selection for white tail spots in the barn swallow in relation to habitat choice by feather lice |journal=Animal Behaviour |volume=58 |issue=6 |pages=1201–1205 |doi=10.1006/anbe.1999.1249 |pmid=10600140 |issn=0003-3472}}</ref>

The breeding season of the barn swallow is variable: in the southern part of the range, the breeding season usually is from February or March to early to mid September, although some late second and third broods finish in October. In the northern part of the range, it usually starts late May to early June and ends the same time as the breeding season of the southernmost birds.<ref name="Turner2010">{{cite book|author=Angela Turner|title=The Barn Swallow|url=https://books.google.com/books?id=bpfGYOqRDW0C&pg=PA113|date=29 January 2010|publisher=Bloomsbury Publishing|isbn=978-1-4081-2821-3|pages=113–114|access-date=14 July 2017|archive-date=26 July 2020|archive-url=https://web.archive.org/web/20200726150441/https://books.google.com/books?id=bpfGYOqRDW0C&pg=PA113|url-status=live}}</ref>

Both sexes defend the nest, but the male is particularly aggressive and territorial.<ref name=Turner/> Once established, pairs stay together to breed for life, but extra-pair [[Mating|copulation]] is common, making this species [[gene]]tically [[Animal sexual behaviour#Polygamy|polygamous]], despite being socially [[monogamy in animals|monogamous]].<ref>
{{cite journal |last=Møller |first=Anders Pape |author2=Tegelstrom, Håkan |s2cid=33591800 |date=November 1997 |title=Extra-pair paternity and tail ornamentation in the barn swallow |journal=Behavioral Ecology and Sociobiology |volume=41 |issue=5 |pages=353–360 |doi=10.1007/s002650050395}}</ref> Males guard females actively to avoid being [[cuckold]]ed.<ref>
{{cite journal |last=Møller |first=Anders Pape |s2cid=24056440 |date=October 1985 |title=Mixed reproductive strategy and mate guarding in a semi-colonial passerine, the swallow ''Hirundo rustica'' |journal=Behavioral Ecology and Sociobiology |volume=17 |issue=4 |pages=401–408 |doi=10.1007/BF00293220|bibcode=1985BEcoS..17..401M }}</ref> Males may use deceptive alarm calls to disrupt extrapair copulation attempts toward their mates.<ref>{{cite journal |last=Møller |first=Anders Pape |year=1990 |title=Deceptive use of alarm calls by male swallows, ''Hirundo rustica'': a new paternity guard |journal=Behavioral Ecology |volume=1 |issue=1 |pages=1–6 |doi=10.1093/beheco/1.1.1}}</ref>

As its name implies, the barn swallow typically nests inside accessible buildings such as barns and stables, or under bridges and wharves.<ref name="Duffin"/> Before man-made sites became common, it nested on cliff faces or in caves, but this is now rare.<ref name=Turner/> 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, algae<ref name="Duffin">{{cite journal|last=Duffin|first=K.|year=1973|title=Barn Swallows use freshwater and marine algae in nest construction|journal=Wilson Bull.|volume=85|pages=237–238}}</ref> or other soft materials.<ref name=Turner/> The nest building ability of the male is also sexually selected; females will lay more eggs and at an earlier date with males who are better at nest construction, with the opposite being true with males that are not.<ref name="SolerCuervo1998">{{cite journal|last1=Soler|first1=Juan José|last2=Cuervo|first2=José Javier|last3=Møller|first3=Anders Pape|last4=De Lope|first4=Florentino|s2cid=12957069|title=Nest building is a sexually selected behaviour in the barn swallow|journal=Animal Behaviour|volume=56|issue=6|year=1998|pages=1435–1442|issn=0003-3472|doi=10.1006/anbe.1998.0938|pmid=9933540}}</ref> After building the nest, 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 {{convert|4|to|8|m2|sqft|sigfig=1|abbr=on}} in size. [[Group size measures|Colony size]] tends to be larger in North America.<ref name= umich/>

[[File:Hirundo rustica -West Sussex, England -chick-8.jpg|right|thumb|A juvenile swallow on a red brick in Sussex]]

In North America at least, barn swallows frequently engage in a [[Mutualism (biology)|mutualist]] relationship with [[osprey]]s. Barn swallows will build their nest below an osprey nest, receiving protection from other birds of prey that 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.<ref name= umich/>

Barn swallows will normally raise two broods, with the original nest being reused for the second brood and being repaired and reused in subsequent years. The female lays two to seven, but typically four or five, reddish-spotted white eggs.<ref name=Turner/> The clutch size is influenced by latitude, with clutch sizes of northern populations being higher on average than southern populations.<ref name="Moller1984">{{cite journal|last1=Moller|first1=Anders Pape|title=Geographical trends in breeding parameters of swallows ''Hirundo rustica'' and house martins ''Delichon urbica''|journal=Ornis Scandinavica|volume=15|issue=1|year=1984|pages=43–54|issn=0030-5693|doi=10.2307/3676002|jstor=3676002}}</ref> The eggs are {{convert|20|x|14|mm|in|frac=8|abbr=on}} in size, and weigh {{convert|1.9|g|gr|abbr=off}}, of which 5% is shell. In Europe, the female does almost all the [[avian incubation|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.<ref name=Turner/> Compared to those from early broods, juvenile barn swallows from late broods have been found to migrate at a younger age, fuel less efficiently during migration and have lower return rates the following year.<ref>{{cite journal |author1= Raja-aho, S. |author2= Eeva, T. | author3= Suorsa, P. |author4= Lehikoinen, E. | year=2017| title= Juvenile Barn Swallows ''Hirundo rustica'' L. from late broods start autumn migration younger, fuel less effectively and show lower return rates than juveniles from early broods | journal=Ibis| volume=159| pages=892–901| doi=10.1111/ibi.12492 | issue=4| doi-access=free }}</ref>

[[File:Barn swallow (feeding) at Tennōji Park in Osaka, June 2016.jpg|Juvenile being fed|thumb|left|alt=A swallow is feeding an insect to another swallow]]

The barn swallow will [[mobbing behavior|mob]] intruders such as cats or [[accipiter]]s that venture too close to their nest, often flying very close to the threat.<ref name = Moller>
{{cite book |last=Møller |first=Anders Pape |year=1994 |title=Sexual Selection and the Barn Swallow |location=Oxford |publisher=Oxford University Press |isbn=978-0-19-854028-1| page=245}}</ref> Adult barn swallows have few predators, but some are taken by accipiters, [[falcon]]s, and [[owl]]s. [[Brood parasite|Brood parasitism]] by [[cowbird]]s in North America or [[cuckoo]]s in Eurasia is rare.<ref name=BWP/><ref name= umich/>

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.<ref name=Turner/> Barn swallow nestlings have prominent red gapes, a feature shown to induce feeding by parent birds. An experiment in manipulating brood size and immune system showed the vividness of the gape was positively correlated with T-cell–mediated immunocompetence, and that larger brood size and injection with an antigen led to a less vivid gape.<ref name="Saino03">{{cite journal|author=Saino, Nicola|author2=Ambrosini, Roberto|author3=Martinelli, Roberta|author4=Ninni, Paola|author5=Møller, Anders Pape |year=2003 |title=Gape coloration reliably reflects immunocompetence of barn swallow (''Hirundo rustica'') nestlings |journal=Behavioral Ecology |volume=14 |issue=1 |pages=16–22 |url=http://www.georgealozano.com/papers/Saino2K03.pdf|doi=10.1093/beheco/14.1.16 |url-status=dead |archive-url=https://web.archive.org/web/20110711084908/http://www.georgealozano.com/papers/Saino2K03.pdf |archive-date=11 July 2011|doi-access=free }}</ref>

The barn swallow has been recorded as [[hybrid (biology)|hybridising]] with the [[American cliff swallow|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.<ref name = Moller/>