Editing Swallow (section)

== Description ==
The Hirundinidae have an evolutionarily conservative body shape, which is similar across the [[clade]], but is unlike that of other [[passerine]]s.<ref name ="HBW">{{ cite book | last=Turner | first=Angela K. | year=2004 | chapter=Family Hirundinidae (Swallows and Martins) | editor1-last=del Hoyo | editor1-first=J. | editor2-last=Elliott | editor2-first=A. | editor3-last=Christie | editor3-first=D.A. | title=Handbook of the Birds of the World | volume=9: Cotingas to Pipits and Wagtails | location=Barcelona, Spain | publisher=Lynx Edicions | isbn=978-84-87334-69-6 | pages=602–685 | chapter-url=https://archive.org/details/handbookofbirdso0009unse/page/602/mode/1up | chapter-url-access=registration }}</ref> Swallows have adapted to hunting insects on the wing by developing a slender, streamlined body and long, pointed wings, which allow great maneuverability and endurance, as well as frequent periods of gliding. Their body shapes allow for very efficient [[bird flight|flight]]; the metabolic rate of swallows in flight is 49–72% lower than equivalent passerines of the same size.<ref name="Hails">{{cite journal|last1=Hails|first1=C.J|title=A comparison of flight energetics in hirundines and other birds|journal=Comparative Biochemistry and Physiology Part A: Physiology|date=1979|volume=63|issue=4|pages=581–585|doi=10.1016/0300-9629(79)90199-3}}</ref>
[[File:Riparia riparia.jpg|thumb|left|The bill of the [[sand martin]] is typical for the family, being short and wide.]]

Swallows have two {{birdgloss|foveae}} in each eye, giving them sharp lateral and frontal vision to help track prey. They also have relatively long eyes, with their length almost equaling their width. The long eyes allow for an increase in visual acuity without competing with the brain for space inside of the head. The morphology of the eye in swallows is similar to that of a raptor.<ref name="TyrrellFernández-Juricic2017">{{cite journal|last1=Tyrrell|first1=Luke P.|last2=Fernández-Juricic|first2=Esteban|title=The hawk-eyed songbird: Retinal morphology, eye shape, and visual fields of an aerial insectivore|journal=The American Naturalist|volume=189|issue=6|year=2017|pages=709–717|issn=0003-0147|doi=10.1086/691404|pmid=28514631|s2cid=3923166}}</ref>

Like the unrelated [[Swift (bird)|swift]]s and [[nightjar]]s, which hunt in a similar way, they have short bills, but strong jaws and a wide gape. Their body lengths range from about {{convert|10|-|24|cm|in |abbr=on}} and their weight from about {{convert|10|-|60|g|oz |abbr=on}}. The smallest species by weight may be the [[Fanti sawwing]], at a mean body mass of {{convert|9.4|g|oz|abbr=on}} while the [[purple martin]] and [[southern martin]], which both weigh in excess of {{convert|50|g|oz|abbr=on}} on average, rival one another as the heaviest swallows.<ref>{{cite book |title=CRC Handbook of Avian Body Masses |edition=2nd |editor-first=John B. Jr. |editor-last=Dunning |publisher=CRC Press |year=2008 |isbn=978-1-4200-6444-5}}</ref> The wings are long, pointed, and have nine primary feathers. The tail has 12 feathers and may be deeply forked, somewhat indented, or square-ended.<ref name ="HBW"/> A long tail increases maneuverability,<ref>{{cite journal|last1=Norberg|first1=R. Ake|title=Swallow Tail Streamer is a Mechanical Device for Self Deflection of Tail Leading Edge, Enhancing Aerodynamic Efficiency and Flight Manoeuvrability|journal=Proceedings of the Royal Society B|date=1994|volume=257|issue=1350|pages=227–233|doi=10.1098/rspb.1994.0119|bibcode=1994RSPSB.257..227N|s2cid=86592049}}</ref><ref name="Buchanan"/> and may also function as a sexual adornment, since the tail is frequently longer in males.<ref name="Buchanan">{{cite journal|last1=Buchanan|first1=Katherine L.|last2=Evans|first2=Matthew R.|title=The effect of tail streamer length on aerodynamic performance in the barn swallow|journal=Behavioral Ecology|date=2000|volume=11|issue=2|pages=228–238|doi=10.1093/beheco/11.2.228|doi-access=free|hdl=10536/DRO/DU:30100792|hdl-access=free}}</ref> In barn swallows, the tail of the male is 18% longer than those of the female, and females select mates on the basis of tail length.<ref name="Moller">{{cite journal|last=Møller|first=Anders pape|year=1992|title=Sexual selection in the monogamous barn swallow (''Hirundo rustica''). II. Mechanisms of sexual selection|journal=Journal of Evolutionary Biology|volume=5|issue=4|pages= 603–624 | doi = 10.1046/j.1420-9101.1992.5040603.x |s2cid=85260912|doi-access=free}}</ref>

Their legs are short, and their feet are adapted for perching rather than walking, as the front toes are partially joined at the base. Swallows are capable of walking and even running, but they do so with a shuffling, waddling gait.<ref name = "leg">{{cite journal|title=Myology of the Leg in Swallows |journal=Auk|year=1969|first=Abbot|last=Gaunt |volume=86 |issue=1|pages=41–53|url=http://sora.unm.edu/node/21819|doi=10.2307/4083540|jstor=4083540|doi-access=free}}</ref> The leg muscles of the river martins (''Pseudochelidon'') are stronger and more robust than those of other swallows.<ref name ="HBW"/><ref name = "leg"/> The river martins have other characteristics that separate them from the other swallows. The structure of the [[Syrinx (bird anatomy)|syrinx]] is substantially different between the two subfamilies;<ref name="Mayr 1951">{{cite journal|last1=Mayr|first1=E.|last2=Amadon|first2=D|title=A Classification of Recent Birds|journal=American Museum Novitates|date=1951|issue=1496|page=16|url=http://digitallibrary.amnh.org/bitstream/handle/2246/3994/N1496.pdf?sequence=1}}</ref> and in most swallows, the bill, legs, and feet are dark brown or black, but in the river martins, the bill is orange-red and the legs and feet are pink.<ref name ="HBW"/>

The most common [[wikt:hirundine|hirundine]] plumage is glossy dark blue or green above and plain or streaked underparts, often white or rufous. Species that [[burrow]] or live in dry or mountainous areas are often matte brown above (e.g. [[sand martin]] and [[crag martin]]). The sexes show limited or no [[sexual dimorphism]], with longer outer tail feathers in the adult male probably being the most common distinction.<ref>{{cite journal|last1=Bańbura|first1=Jerzy|title=Sexual dimorphism in wing and tail length as shown by the Swallow ''Hirundo rustica''|journal=Journal of Zoology|date=1986|volume=201|issue=1|pages=131–136|doi=10.1111/j.1469-7998.1986.tb03625.x}}</ref>

The chicks hatch naked and with closed eyes.<ref name="Gill1995">{{cite book|last=Gill|first=Frank B.|title=Ornithology|url=https://books.google.com/books?id=jFfs1jsPfwgC&pg=PA434|year=1995|publisher=W. H. Freeman|isbn=978-0-7167-2415-5|page=434}}</ref> Fledged juveniles usually appear as duller versions of the adult.<ref name = Turner/>