Sunning (behaviour)

Birds adopt special postures when sunning, these may include spreading out their feathers, flattening their body on soil, showing either their upper parts to the Sun or facing the Sun. Some authors separate the behaviours into sun-basking and sun-exposure {{endash}} the former term used when the behaviour is strictly thermoregulatory in function while the latter term may be more appropriate if the behaviour serves functions other than raising body temperature.

In some species, the sunbathing posture is adopted in very hot weather and the birds sometimes stay in close contact with hot soil. Birds may fluff up their feathers, expose their preen-gland, lean to one side and so on. The wings may be turned inside out as in the boobies or held in delta-wing positions as in herons and storks or held outspread as by vultures.{{cite book|pages= 569–560 |title=A Dictionary of Birds| author1=Campbell, Bruce| author2=Lack, Elizabeth| publisher=A & C Black| year=2013}}{{cite journal|author=Hauser, D.C.|year= 1957|title= Some observations on sun-bathing in birds|journal= Wilson Bulletin|volume= 69 |pages=78–90 |url=https://sora.unm.edu/sites/default/files/journals/wilson/v069n01/p0078-p0090.pdf }} Swallows were observed to indulge in the activity for very short durations and this appeared to induce hyperthermia leading to them gaping to cool. Observers have suggested that the purpose might not be thermoregulation in these cases.{{cite journal|title=Some observations on sunbathing in swallows| journal=Journal of Field Ornithology| volume=63| issue=1| pages=53–56| author1=Blem, C.R.| author2=Blem, L.B.}} A theory that birds obtained vitamin D by allowing precursors in the preen-gland secretions to be converted by ultraviolet radiation is considered to be unsupported.{{Cite journal| journal=Zeitschrift für Tierpsychologie|volume=30|issue=3|pages=253–258|year=1972| title=Sunbathing in birds|author=Mueller, Helmut C.|doi=10.1111/j.1439-0310.1972.tb00853.x}}{{cite journal|author=Kennedy, R.J.|year= 1969|title= Sunbathing behaviour of birds|journal= British Birds |volume=62|pages=249–258|url= https://britishbirds.co.uk/wp-content/uploads/article_files/V62/V62_N07/V62_N07_P249_258_A055.pdf }} Large soaring birds such as Gyps vultures may use sun-bathing postures to help in stiffening their feathers as they used such postures only prior to flying and not during the early morning hours.{{cite journal|author=Houston, D.C.|year=1980|title=A possible function of sunning behaviour by griffon vultures, Gyps spp., and other large soaring birds |journal=Ibis |volume=122|issue=3|pages=366–369 |doi= 10.1111/j.1474-919X.1980.tb00892.x}} Another theory is that ectoparasites may be killed or forced to move away from inaccessible parts of the body to more accessible areas where they can be removed through preening. This is supported by the observation that sunning is often followed by preening.{{cite journal|first=Derek |last=Goodwin| year= 1967 |title=Some possible functions of sun-bathing in birds|journal= British Birds |volume=60|pages=362–364|url= https://britishbirds.co.uk/wp-content/uploads/article_files/V60/V60_N09/V60_N09_P363_364_A061.pdf }}{{cite journal|doi=10.1098/rstb.2017.0196|pmid=29866911|pmc=6000146|title=Anti-parasite behaviour of birds|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=373|issue=1751|pages=20170196|year=2018|last1=Bush|first1=Sarah E.|last2=Clayton|first2=Dale H.}} Feather-degrading bacteria are known to be killed by the action of sunlight.{{cite journal|doi=10.1676/05-123.1|title=Sunlight on Feathers Inhibits Feather-Degrading Bacteria|journal=The Wilson Journal of Ornithology|volume=119|issue=2|pages=239–245|year=2007|last1=Saranathan|first1=Vinodkumar|last2=Burtt|first2=Edward H.|s2cid=84253238}}

File:Marsh wren sunning (41685).jpg|Marsh Wren sunbathing

File:20240702 sunbathing great crested flycatcher south meadows PD203700 01.jpg|Great Crested Flycatcher, Sunbathing

File:Asian openbill at Keoladeo national park (Jan,2023) 09.jpg|Asian openbill

Basking is common to most active diurnal reptiles. Lizards, crocodiles, terrapins, and snakes routinely make use of the morning sun to raise their body temperature. Freshwater turtles and terrapins have been found to bask and raise their body temperature close to the highest temperatures that they can tolerate.{{cite journal|title=Ecology of the Basking Habit in Turtles| author=Boyer, Don R.|journal=Ecology| volume=46| issue=1/2|year= 1965|pages= 99–118 |jstor=1935262| doi=10.2307/1935262| bibcode=1965Ecol...46...99B}}

File:Peninsular rock agama basking 2.jpg|Psammophilus agama basking

File:Marsh crocodile - Basking in the sun.jpg|Crocodylus palustris basking

File:Sheldonbasking.JPG| Captive Trachemys scripta elegans basking

File:Physignathus lesueurii howittii.jpg|Gippsland water dragon

File:Dimetrodon NT2 small.jpg|Dimetrodon may have used the sail on its back to gather heat

File:Turtle rock in Prospect Park (01717).jpg|Pond sliders and a river cooter struggle for space on a rock to bask

File:Tabby sunning after winter in house.jpg basking]]

Some mammals and most humans make use of the sun to warm their body or to provide comfort. It has been suggested that early mammals, which may have been small and nocturnal, may have basked to rapidly warm their bodies based on observations made on a nocturnal marsupial, Pseudantechinus macdonnellensis.{{cite journal|doi=10.1007/s00114-002-0349-4|pmid=12435094|title=Was basking important in the evolution of mammalian endothermy?|journal=Naturwissenschaften|volume=89|issue=9|pages=412–414|year=2002|last1=Geiser|first1=Fritz|last2=Goodship|first2=Nicola|last3=Pavey|first3=Chris|bibcode=2002NW.....89..412G|s2cid=7203160}}

File:PARNASSIAN_EVERSMANN'S_(Parnassius_eversmanni)_(6-25-2016)_denali_highway,_mile_p13_pass,_near_paxson,_alaska_(1)_(28494231274).jpg, a typical alpine butterfly with dark markings close to the body that help gather heat from the sun and forage early]]

Many insects require the morning sun to come out of nocturnal torpor and become active. In the higher latitudes, many insects have black on their wings or body to enhance their heat acquisition. This trend for increased darkness in higher latitudes is especially well marked in the Lepidoptera although the trend may be more general and unrelated to thermoregulation as it is also seen in nocturnal Geometridae.{{cite journal|doi=10.1111/geb.12703|title=The dark side of Lepidoptera: Colour lightness of geometrid moths decreases with increasing latitude|journal=Global Ecology and Biogeography|volume=27|issue=4|pages=407–416|year=2018|last1=Heidrich|first1=Lea|last2=Friess|first2=Nicolas|last3=Fiedler|first3=Konrad|last4=Brändle|first4=Martin|last5=Hausmann|first5=Axel|last6=Brandl|first6=Roland|last7=Zeuss|first7=Dirk|bibcode=2018GloEB..27..407H }}

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Category:Ethology