View source for Biology:Xerocole

{{Short description|Any animal adapted to live in the desert}}
[[File:Fennec Fox @ Africa Alive,  Lowestoft 2.jpg|thumb|alt=A fennec fox standing around in tall grass.|The fennec fox's large ears help keep it cool: when the blood vessels dilate, blood from the body cycles in and dissipates over the expanded [[Surface area|surface area]].<ref name=buzzle />]]
A '''xerocole''' ({{etymology|gre|xēros {{IPAc-en|ˈ|z|ɪ|r|oʊ|s}}|dry|la|col(ere)|to inhabit}}),<ref>{{cite encyclopedia|title=xero-|encyclopedia=The New Oxford American Dictionary|edition=2nd|date=2005|publisher=Oxford University Press, Inc.}}</ref><ref>{{cite encyclopedia| publisher = Trafford Publishing| isbn = 9781553698869| last = Aldrich| first = Chris| encyclopedia = The Aldrich Dictionary of Phobias & Other Word Families| date = 1 December 2002|title=–COLE|page=17}}</ref><ref>{{cite book | publisher = Taylor & Francis US | isbn = 9781439836514 | last = Barrows | first = Edward M. | title = Animal Behavior Desk Reference: A Dictionary of Animal Behavior, Ecology, and Evolution | date = 20 April 2011|page=99 }}</ref> is a general term referring to any animal that is adapted to live in a [[Earth:Desert|desert]]. The main challenges xerocoles must overcome are lack of water and excessive heat. To conserve water they avoid evaporation and concentrate excretions (i.e. urine and feces).<ref name=buzzle>{{cite web|url=http://www.buzzle.com/articles/desert-animals-list.html|work=Buzzle|title=Desert Animals List|first=Shashank|last=Nakate|date=20 September 2011|access-date=24 November 2012|archive-url=https://web.archive.org/web/20121105154333/http://www.buzzle.com/articles/desert-animals-list.html|archive-date=5 November 2012|url-status=dead}}</ref> Some are so adept at conserving water or obtaining it from food that they do not need to drink at all. To escape the desert heat, xerocoles tend to be either [[Biology:Nocturnality|nocturnal]] or crepuscular (most active at dawn and dusk).

==Water conservation==
[[File:Merriam's kangaroo rat (Dipodomys merriami).jpg|thumb|left|A kangaroo rat can live its entire life without ever having to drink.<ref name=roberts86 />]]

===Avoiding evaporation===
Xerocoles have developed a variety of mechanisms to reduce water loss via evaporation. Mammalian xerocoles sweat much less than their non-desert counterparts. For example, the camel can survive ambient temperatures as high as {{convert|49|°C|°F|0|abbr=on}} without sweating,<ref name=national-geo >{{cite web|title=Arabian (Dromedary) Camel|access-date=25 November 2012|publisher=National Geographic Society|work=National Geographic|url=https://www.nationalgeographic.com/animals/mammals/facts/arabian-camel}}</ref> and the [[Biology:Kangaroo rat|kangaroo rat]] lacks sweat glands entirely.<ref name=sharma05 >{{cite book | publisher = RaGORI Publications | isbn = 9788171339051 | last = P.D | first = Sharma | title = Ecology And Environment | date = 2005|pages=95–96 }}</ref> Both birds and mammals in the desert have oils on the surface of their skin to "waterproof" it and inhibit evaporation.<ref name=roberts00>{{cite book | publisher = Nelson Thornes | isbn = 9780174387329 | last1 = Roberts | first1 = M. B. V. | first2 = Michael Jonathan|last2=Reiss|first3=Grace|last3=Monger|title = Advanced Biology | date = 23 June 2000|pages=294–296}}</ref>

Desert insects use a similar method, as their [[Biology:Arthropod cuticle|cuticle]]s are [[Physics:Wax|wax]]y to prevent water from escaping; however, at critical temperatures (ex. {{convert|30|°C|°F|0|abbr=on}} for cockroaches), the wax molecules in the cuticle rearrange to become permeable and permit evaporative cooling.<ref name=roberts86 >{{cite book | publisher = Nelson Thornes | isbn = 9780174480198 | last = Roberts | first = Michael Bliss Vaughan | title = Biology: A Functional Approach | date = 1986|pages=225–227, 234–235, 240}}</ref>

Amphibious xerocoles, such as species of the frog genus ''[[Biology:Phyllomedusa|Phyllomedusa]]'', have wax-like coatings on their skin to reduce water loss. The frogs secrete lipids from glands in their skin: when their skin begins to dry out, they move their limbs over the glands on their backs, and wipe the lipids over their bodies.<ref name=mares-animaladapt>{{cite book|last = Caldwell|first = Janalee P|chapter=Animal adaptations|pages=24–27|title=Deserts|year = 1999|isbn = 9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA24}}</ref> Other desert amphibians, such as the frog genus ''[[Biology:Cyclorana|Cyclorana]]'', avoid desiccation by burrowing underground during dry periods and forming a cocoon from shed skin: rather than being sloughed off, the skin remains attached to create the cocoon. As skin layers amass, [[Physics:Semipermeable membrane|water impermeability]] increases.<ref name=mares-animaladapt /><ref name=mares-amphibians>{{cite book|last = Caldwell|first = Janalee P|chapter=Amphibians|pages=19–22|title=Deserts|year = 1999|isbn = 9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA19}}</ref>

====During evaporation====
Though desert birds lack sweat glands, they can still take advantage of evaporative cooling by panting, which cools the trachea and lungs, and gular flapping, which consists of rapidly fluttering the [[Biology:Gular skin|gular skin]] to move air over the inner mouth and throat.<ref name=mares-birds>{{cite book|chapter=Birds|pages=74–75|title=Deserts|isbn=9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA74|last1=Mares|first1=Michael A.|year=1999}}</ref> Kangaroo rats and other small mammals use evaporative cooling in a similar way. When air is [[Physics:Breathing|respired]], water evaporates from the nose, cooling the surface of the nasal passages to approximately {{convert|24|°C|°F|0|abbr=on}}. The low temperature causes moisture to condense, partially making up for the water that was lost.<ref name=mares-animaladapt /><ref name=rastogi71>{{cite book | publisher = New Age International | isbn = 9788122412796 | last = Rastogi | first = S. C. | title = Essentials Of Animal Physiology | date = 1971|pages=180–181, 198, 200, 204 }}</ref> The process, called respiratory heat exchange, works best when the walls of the nasal passage have a large surface area.<ref name=feldhamer07 />

Some animals pour bodily fluids on themselves to take advantage of evaporative cooling. Xerocole birds such as [[Biology:Stork|stork]]s, [[Biology:New World vulture|New World vulture]]s, and [[Biology:Ibis|ibis]] urinate on their legs,<ref name=mares-birds /><ref name=mares-ibis>{{cite book|chapter=Ibis|pages=289–290|first=Stephen C|last=Lougheed|title=Deserts|year=1999|isbn=9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA289}}</ref> while desert tortoises sometimes salivate on their neck and front legs to keep cool.<ref name=roberts86 /> Similarly, many rodents and marsupials lick themselves to spread saliva, though this only remains effective for a short time, and requires the fur to become very damp.<ref name=feldhamer07 />

===Excretion===

====Urine====
[[File:Bilma-Salzkarawane2.jpg|thumb|250px|alt=Camels carrying baggage in the desert|Arabian camels can survive several days and travel up to {{convert|160|km|mi|-2}} without water.<ref name=roberts86 /><ref name=national-geo /> One way they save water is by excreting very concentrated urine.<ref name=sharma05 />]]
To excrete nitrogenous waste products, mammals (and most amphibians) excrete [[Chemistry:Urea#Physiology|urea]] diluted in water.<ref name=mares-kidneyfunction>{{cite book|chapter=Klipspringer|page=324|first=Thomas E|last=Lacher Jr.|title=Deserts|year=1999|isbn=9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA324}}</ref><ref name=virtual-chembook>{{cite web|url=http://www.elmhurst.edu/~chm/vchembook/633ureacycle.html |title=Urea Cycle |first=Charles E. |last=Ophardt |publisher=Elmhurst College |work=Virtual Chembook |access-date=26 November 2012 |url-status=dead |archive-url=https://web.archive.org/web/20121115153648/http://www.elmhurst.edu/~chm/vchembook/633ureacycle.html |archive-date=November 15, 2012 }}</ref> Such xerocoles have adapted to make their urine as concentrated as possible (i.e. use the least amount of water) to dissolve urea. Desert mammals have longer and more deeply inset nephrons,<ref name=munkasci65 >{{cite journal | issn = 0009-7330 | volume = 17 | issue = 4 | pages = 303–311 | last1 = Munkácsi | first1 = I. | first2 = M.|last2= Palkovits | title = Volumetric analysis of glomerular size in kidneys of mammals living in desert, semidesert or water-rich environment in the Sudan | journal = Circulation Research | date = October 1965|url=http://circres.ahajournals.org/content/17/4/303.full.pdf|pmid=4953625 | doi=10.1161/01.res.17.4.303| s2cid = 44221968 | doi-access = free }}</ref> as well as smaller and fewer cortical and juxtamedullary glomeruli (glomeruli being capillary networks where both fluid and waste are extracted from blood). This in turn leads to a smaller [[Medicine:Glomerular filtration rate|glomerular filtration rate]], and on the whole, less water is transferred from the blood to the kidney.<ref name=roberts86 /><ref name=munkasci65 /><ref name=gale08 >{{cite encyclopedia | publisher = The Gale Group, Inc. | title = glomeruli | encyclopedia = Gale Encyclopedia of Medicine | date = 2008 | url = http://medical-dictionary.thefreedictionary.com/glomeruli|access-date=27 November 2012 }}</ref> The kidneys of desert mammals are also better adapted at reabsorbing water from the tubular fluid: though there are fewer glomeruli, the xerocole has larger juxtamedullary glomeruli than cortical glomeruli (the former playing an important role in concentrating urine),<ref name=cliffs>
{{cite web
 |title=Regulation of Urine Concentration 
 |url=http://www.cliffsnotes.com/study_guide/Regulation-of-Urine-Concentration.topicArticleId-277792,articleId-277776.html 
 |work=Anatomy & Physiology 
 |publisher=CliffsNotes 
 |access-date=27 November 2012 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20121025033759/http://www.cliffsnotes.com/study_guide/Regulation-of-Urine-Concentration.topicArticleId-277792,articleId-277776.html 
 |archive-date=October 25, 2012 
}}</ref> whereas the opposite is true for non-xerocoles. Desert mammals also have longer loops of Henle, structures whose efficiency in concentrating urine is directly proportional to their length.<ref name=roberts86 /><ref name=munkasci65 /><ref name=mares-kidney>{{cite book|chapter=Kidneys|pages=323–324|first=E. Annette|last=Halpern|title=Deserts|year=1999|isbn=9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA323}}</ref> The efficiency of their loops of Henle is augmented by the increased antidiuretic hormone in their blood.<ref name=roberts86 />

Desert amphibians can store more nitrogen than aquatic ones, and do so when not enough water is available to excrete the nitrogen as urea.<ref name=mares-amphibians /> The [[Biology:Hyperolius|African reed frog]] can store excess nitrogen in [[Biology:Chromatophore#Iridophores and leucophores|iridophore]], pigmented [[Biology:Granule (cell biology)|granules]] in its skin, by converting the nitrogen to [[Chemistry:Guanine|guanine]], which makes up the majority of the iridophores' composition.<ref name=mares-animaladapt />

Reptiles, birds, insects, and some amphibious species excrete nitrogenous waste as [[Chemistry:Uric acid|uric acid]] rather than urea. Because uric acid is less toxic than urea, it does not need to be dissolved in water to be excreted (as such, it is largely insoluble).<ref name=mares-amphibians /><ref name=mares-kidneyfunction /><ref name=virtual-chembook /><ref name=mares-kidney />

====Feces====
Most animal feces are over 75% water; xerocoles, however, reabsorb water in the gut and produce much drier feces.<ref name=rodriguez12 >{{cite book | publisher = Enslow Publishers, Inc. | isbn = 9780766036970 | last = Rodríguez | first = Ana María | title = Gray Foxes, Rattlesnakes, and Other Mysterious Animals of the Extreme Deserts | date = 1 February 2012 | page = 27}}</ref> For example, the kangaroo rat's feces contain only {{frac|1|6}} as much water as that of other, non-desert rodents.<ref name=miller64>{{cite book | publisher = University of California Press | isbn = 9780520008663 | last1 = Miller | first1 = Alden Holmes | first2 = Robert Cyril |last2 = Stebbins | title = The Lives of Desert Animals in Joshua Tree National Monument | date = 1964 |page=9 }}</ref> In insects, the rectal gland also absorbs water, and the insects excrete dry pellets.<ref name=rodriguez12 /> In birds, along with some other vertebrates, the ureter and [[Biology:Rectum|rectum]] both lead to the [[Biology:Cloaca|cloaca]], whose walls also absorb water.<ref name=roberts86 /><ref name=roberts00 />

===Other methods===
Camels can further conserve water by closing an orifice in their stomach to create two compartments: one for water and one for food.<ref name=schmidt52 >{{cite journal| issn = 	0031-9333| volume = 32| issue = 2| pages = 135–166| last1 = Schmidt-Nielsen| first1 = Knut| first2 = Bodil| last2=Schmidt-Nielsen|title=Water Metabolism of Desert Mammals| journal = Physiological Reviews| access-date = 25 September 2012| date = 1 April 1952| doi = 10.1152/physrev.1952.32.2.135|url=http://physrev.physiology.org/content/32/2/135}}</ref>

Seed-eating rodents maintain a low metabolic rate to reduce water lost to respiration (and to prevent their burrow from overheating). Rodent mothers produce concentrated milk for their young, and then eat their young's dilute urine and feces to regain some of the water that was lost. Desert [[Biology:Canids|canids]] and kangaroos eat their own young's excrement for the same reason.<ref name=feldhamer07 />

The Australian [[Biology:Cyclorana platycephala|water-holding frog]] conserves water by retaining urine in the [[Biology:Bladder|bladder]], swelling up like a balloon; it then uses its bladder as a water reserve during the dry season.<ref name=roberts00 /><ref name=mares-amphibians />

==Alternative water sources==
[[File:Addax 039.jpg|thumb|right|upright|alt=An addax's face – he's looking into the camera and raising his upper lip, making it look as though he's laughing.|Some antelope, such as the [[Biology:Addax|addax]] (pictured) and the oryx, are so efficient at getting water from plants that they never need to drink.<ref name=feldhamer07 /><ref name=mares-addax >{{cite book|last = Lacher Jr.|first = Thomas E|chapter=Addax|page=7|title=Deserts|year = 1999|isbn = 9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA7}}</ref>]]
Xerocoles get a substantial amount of [[Biology:Hygroscopy|hygroscopic]] water from their food. Many feed on moisture-filled plants: the [[Biology:Aardvark|aardvark]] obtains water from wild cucumbers (''[[Biology:Cucumis humifructus|Cucumis humifructus]]'')<ref name=mares-aardvark>{{cite book|last = Lacher Jr.|first = Thomas E|chapter=Aardvark|page=3|title=Deserts|year = 1999|isbn = 9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA3}}</ref> and the camel eats succulents and bushes in the winter, getting enough water to go two months without drinking.<ref name=rastogi71 /> The [[Biology:Oryx|oryx]] eats ''[[Biology:Acacia|Acacia]]'' leaves late at night, when water content is highest: in the hot, arid daytime the leaves are only 1% water; but in cooler, more humid night the leaves are 40% water. Some xerocoles are able to obtain water from [[Biology:Halophyte|halophytic (saltwater) plants]], as they can metabolize high amounts of [[Chemistry:Oxalic acid|oxalic acid]] and produce very concentrated urine. The chisel-toothed kangaroo rat also mitigates the saltiness of the halophyte it eats (the shadscale) by using its broad, sharp lower incisors to scrape off the leaves' salty outerlayer to reach the less-salty center.<ref name=feldhamer07>{{cite book | publisher = JHU Press | isbn = 9780801886959 | last1 = Feldhamer | first1 = George A. | first2 = Lee C. | last2 = Drickamer | first3 = Stephen H. | last3 = Vessey | first4 = Joseph F. | last4 = Merritt | first5 = Carey | last5 = Krajewski | title = Mammalogy: Adaptation, Diversity, Ecology | chapter = Environmental Adaptations | date = 7 September 2007 | pages = [https://archive.org/details/mammalogyadaptat03edunse/page/176 176–190] | chapter-url = https://archive.org/details/mammalogyadaptat03edunse/page/176 }}</ref>

Carnivores derive water from their prey's meat and blood.<ref name=sharma05 /><ref name=feldhamer07 /> Insectivores, such as the [[Biology:Aardwolf|aardwolf]] (a type of hyena) and the [[Biology:Southern grasshopper mouse|southern grasshopper mouse]], are thus largely independent from free water.<ref name=feldhamer07 /><ref name=mares-aardwolf>{{cite book|last = Braun|first = Janet K|chapter=Aardwolf|pages=3–4|title=Deserts|year = 1999|isbn = 9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA3}}</ref>

Xerocoles obtain a large percentage of their water from the [[Biology:Metabolism|metabolic processes]] used to break down their food. The water gained from fat is nearly twice the amount gained from carbohydrates, as the former contains more hydrogen (which determines the amount of water produced). The water gained from metabolism is more than enough to offset the water lost from evaporation in the lungs (which increases due to the need for oxygen to break down food).<ref name=roberts86 /><ref name=sharma05 /><ref name=rastogi71 />

==Thermal regulation==

===Morphology===
Xerocoles such as the [[Biology:Lepus|hare]] have large ears that help them keep cool: when the ears stand up, blood flow increases to the numerous vessels there and heat is dissipated.<ref name=sharma05 /><ref name=biomimicry>{{cite web | publisher = The Biomimicry 3.8 Institute | title = Large ears used to cool off: jackrabbit| work = Ask Nature | access-date = 2012-12-03 | date = 2012-06-23 | url = http://www.asknature.org/strategy/a250478ba7f69e68c71405d931c91d62 }}</ref> However, at {{convert|48|°C|°F|0|abbr=on}}, the [[Biology:Cape hare|cape hare]] near [[Place:Abu Dhabi|Abu Dhabi, UAE]] sits in the shade and drapes its ears over itself, as erecting them in such weather would absorb more heat.<ref name=abudhabi>{{cite news | title = Desert hares | work = The National | location = United Arab Emirates | access-date = 2012-12-03 | url = http://www.thenational.ae/guide/historical/flora-and-fauna/desert-hares/desert-hares | publisher=Abu Dhabi Media }}</ref>

Desert animals have less fat than their non-desert counterparts, as fat would act as insulation, so retaining heat. What fat they do have is localized, such as in the camel's hump or the [[Biology:Plains bison|bison's]] neck.<ref name=roberts86 /> In terms of fur, however, desert animals have thick insulating coats that impede the conduction of heat towards the body.<ref name=sharma05 /> The coats are not uniformly distributed, but rather leave sparsely covered patches called "thermal windows" at the axilla, [[Medicine:Groin|groin]], scrotum, and [[Biology:Mammary gland|mammary gland]]s. Heat can be dissipated from thermal windows via [[Astronomy:Convection|convection]] and conduction.<ref name=feldhamer07 />

Similarly, desert birds have fewer feathers on the underwing and flank – heat stress induces some birds to raise their wings, increasing the surface area of exposed skin. Birds adjust their feathers to create or dissipate an insulating layer, as typified by the [[Biology:Ostrich|ostrich]]. At high temperatures, the ostrich elevates its long dorsal feathers to create a barrier against solar radiation while allowing air to move across the skin's surface. In the cool nights, the feathers lower and interlock, trapping an insulating layer above the skin.<ref name="mares-birds"/>

[[File:Cunningham skink448.jpg|thumb|left|alt=A reddish-gold lizard basking on a log|Ectotherms, such as this Cunningham's spiny-tailed skink, often bask in the sun to regulate body temperature.]]

===Burrows===
Most small xerocoles live in [[Biology:Burrow|burrow]]s to avoid the desert heat.<ref name=silverstein08>{{cite book | publisher = Twenty-First Century Books | isbn = 9780822534341 | last1 = Silverstein | first1 = Alvin | first2 = Virginia B | last2 = Silverstein | first3 = Virginia | last3 = Silverstein<!--No, really.--> | first4 = Laura | last4 = Silverstein Nunn | title = Adaptation | date = 2008 | pages = [https://archive.org/details/adaptation0000silv/page/42 42–43] | url-access = registration | url = https://archive.org/details/adaptation0000silv/page/42 }}</ref> The burrows act as microenvironments: when they are deeper than {{convert|50|–|60|cm|in|abbr=on}} below the surface, they maintain humidity and temperatures between {{convert|30|and|32|C|F|abbr=on}}, regardless of external weather.<ref name=feldhamer07 /><ref name=mares-gopher>{{cite book|chapter=Gopher|page=243|first=Janet K|last=Braun|title=Deserts|year=1999|isbn=9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA243}}</ref> Some animals seal their burrows to keep them moist.<ref name=sharma05 /><ref name=mares-iguana>{{cite book|chapter=Iguana, Desert|pages=290–291|first=Laurie J|last=Vitt|title=Deserts|year=1999|isbn=9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA290}}</ref>

Ectotherms also use burrows as a means to keep warm in the cold desert nights.<ref name=roberts86 /> As ectotherms are usually small and unable to store their own body heat, they quickly take on the external temperature of the environment, which necessitates controlled microenvironments. For example, while reptiles are able to operate at temperatures exceeding optima, they become sluggish when cold. As such, they spend their nights in burrows or crevices, where they create warm environments by quickly generating metabolic heat.<ref name=roberts86 /><ref name=rundel05>{{cite book | publisher = Cambridge University Press | isbn = 9780521021418 | last1 = Rundel | first1 = Philip Wilson | first2 = Arthur C.|last2=Gibson | title = Ecological Communities And Processes in a Mojave Desert Ecosystem: Rock Valley, Nevada | date = 30 September 2005|chapter=Adaptations of Mojave Desert Animals |pages=132–138}}</ref> Desert lizards usually use other animals' burrows to meet their purposes.<ref name=mares-animaladapt />

===Circadian rhythms===
All desert rodents except ground squirrels and [[Biology:Chipmunk|chipmunk]]s are nocturnal.<ref name=feldhamer07 /> Amphibians are usually nocturnal as well, while many other xerocoles are [[Biology:Diurnality|diurnal]], but reduce activity at midday and increase in the mornings and evenings.<ref name=mares-animaladapt /> Some xerocoles change their activity patterns depending on the season: nocturnal ants, for example, become diurnal during colder periods.<ref name=mares-actcycles >{{cite book|last = Caldwell|first = Janalee P|chapter=Activity cycles, animals|page=5|title=Deserts|year = 1999|isbn = 9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA5}}</ref>

Many xerocoles, especially rodents, estivate in the summer, becoming more dormant.<ref name=roberts86 /> Some desert amphibians estivate underground for over a year at a time.<ref name=mares-amphibians /> Unlike [[Biology:Hibernation|hibernation]], which leads to a state of [[Biology:Torpor|torpor]], estivation induces lethargy, and can go unnoticed in some animals if their body temperature is not measured.<ref name=feldhamer07 />

==Protection from the sun==
[[File:Xerus inauris 1.jpg|thumb|alt=Three cape ground squirrels emerging from a burrow in the Namib Desert|When the Cape ground squirrel scurries from one shady spot to the next, it holds its wide, flat tail over its back to provide shade.<ref name=feldhamer07 />]]
Xerocoles are usually light and sandy in color as a means to reflect solar radiation and reduce heat absorption.<ref name=rundel05 /> Some change color with the seasons to reflect more sunlight in the summer: addaxes change from gray-brown to nearly white.<ref name=mares-addax /><ref name=mares-camel>{{cite book|chapter=Camel|pages=96–97|first=E. Anette|last=Halpern|title=Deserts|year=1999|isbn=9780806131467|chapter-url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA96}}</ref> Iguanid lizards can change color on a much smaller time scale by varying [[Chemistry:Melanin|melanin]] concentration. They become darker when burrowing and lighter when basking – both the [[Biology:Desert iguana|desert iguana]] and the [[Biology:Zebra-tailed lizard|zebra-tailed lizard]] become so pale that they appear to shine due to the amount of light they reflect.<ref name=rundel05 />

Most desert lizards also have a black peritoneal lining in their abdominal cavity to absorb UV radiation and prevent it from damaging internal organs.<ref name=mares-animaladapt />

Shade under shrubbery provides resting spots for diurnal lizards, nesting sites for birds, as well as temporary oases for diurnal rodents, who skirt among shady spots.<ref name=feldhamer07 /> Large animals such as camels and carnivores also spend the hottest parts of the day under shade.<ref name=silverstein08 /><ref name=rundel05 />

==Protection from sand==
Desert animals such as the camel, addax, and kangaroo rat have large feet to prevent them from sinking in the sand.<ref name=national-geo /><ref name=silverstein08 /> The [[Biology:Fennec fox|fennec fox]] has extra fur on the soles of its feet to give it traction and protect it from the hot sand.<ref name=seaworld>{{cite journal|publisher=SeaWorld/Busch Gardens |title=Animal Adaptations |date=December 2002 |url=http://www.seaworld.org/just-for-teachers/classroom-activities/4-8/pdf/Desert%20Animal%20Adaptations.pdf |journal=Classroom Activities |url-status=dead |archive-url=https://web.archive.org/web/20120915051730/http://www.seaworld.org/just-for-teachers/classroom-activities/4-8/pdf/Desert%20Animal%20Adaptations.pdf |archive-date=September 15, 2012 }}</ref> Most animals in arid environments are slender with long legs, giving them the speed as they travel long distances for food and water.<ref name=cloudsley57>{{cite news | issn = 0262-4079 | volume = 2 | issue = 29 | last = Cloudsley-Thompson | first = J. L. | publisher = Reed Business Information | title = The Earth's increasing deserts | newspaper = New Scientist | date = 6 June 1957 |url=https://books.google.com/books?id=zh2TN99OsaQC&pg=PA30 }}</ref>

The three main vulnerabilities against the sand are through the eyes, ears, and nose.<ref name=lull20>{{cite book| publisher = Macmillan| last = Lull| first = Richard Swann| title = Organic evolution| date = 1920|chapter-url=https://books.google.com/books?id=F-E-AAAAYAAJ&pg=PA393|chapter=Desert Adaptations|pages=393–408}}</ref> To keep sand out of their eyes, xerocoles including reptiles and birds, and some amphibians and mammals<ref name=butler05>{{cite book| publisher = John Wiley & Sons| isbn = 9780471733836| last1 = Butler| first1 = Ann B.| first2 = William |last2= Hodos| title = Comparative Vertebrate Neuroanatomy: Evolution and Adaptation| url = https://archive.org/details/comparativeverte00butl_744| url-access = limited| date = 2 September 2005|page=[https://archive.org/details/comparativeverte00butl_744/page/n239 215]}}</ref> have a [[Biology:Nictitating membrane|nictitating membrane]] in their eyes: a third, transparent eyelid that protects the cornea from blowing sand and can dislodge it from the eye.<ref name=seaworld /><ref name=butler05 /> Reptiles also have eyes the size of pinholes or protected by valves.<ref name=lull20 /> To keep sand out of their ears, mammals such as the camel and the [[Biology:Sand cat|sand cat]] have long hairs protruding from them.<ref name=bronxzoo>{{cite web|author=Bronx Zoo |title=Camel Adaptations |access-date=29 November 2012 |url=http://www.bronxzoo.com/files/engage.html |publisher=Wildlife Conservation Society |format=Flash |url-status=dead |archive-url=https://web.archive.org/web/20120626071454/http://www.bronxzoo.com/files/engage.html |archive-date=June 26, 2012 }}</ref><ref name=lincolnpark>{{cite web | author = Lincoln Park Zoo | title = Sand cat | access-date = 6 December 2012 | date = 23 September 2010 | url = http://www.lpzoo.org/animals/factsheet/sand-cat }}</ref> The camel and the [[Biology:Saiga antelope|saiga antelope]] also have adaptations to protect their noses from sand: the former has narrow nostrils it can close, and the latter has a large nose with its nostrils set wide apart and far back to prevent sand from entering when grazing.<ref name=silverstein08 /><ref name=cloudsley57 /><ref name=amnh>{{cite web| publisher = American Museum of Natural History| title = Camels| work = Traveling the Silk Road| access-date = 8 December 2012| url = http://www.amnh.org/exhibitions/past-exhibitions/traveling-the-silk-road/take-a-journey/samarkand/camels}}</ref> Reptile diggers have nostrils that face upwards instead of forwards for the same reason.<ref name=lull20 />

==Speed==
Xerocoles, having to travel long distances for food and water, are often adapted for speed, and have long limbs, feet that prevent them from sinking in the sand, and are overall slender in form.<ref name=cloudsley57 /> As there is little cover to protect them from predators, desert animals also use speed as a defense mechanism. For example, a desert jackrabbit can run much faster than a coyote; as such, "an ordinary wolf or coyote will not attempt to chase him, for they realize the hopelessness of it."<ref name=lull20 />

==Known xerocoles==
The following animals are known xerocoles:

{{div col|colwidth=15em}}
* [[Biology:Aardvark|Aardvark]]
* [[Biology:Aardwolf|Aardwolf]]
* [[Biology:Acanthodactylus|Acanthodactylus]]
* [[Biology:Addax|Addax]]
* [[Biology:African leopard|African leopard]]
* [[Biology:Lion|African lion]]
* [[Biology:African savanna hare|African savanna hare]]
* [[Biology:African wild ass|African wild ass]]
* [[Biology:African wild dog|African wild dog]]
* [[Biology:American badger|American badger]]
* [[Biology:Antelope jackrabbit|Antelope jackrabbit]]
* Ankole-Watusi
* Arabian camel
* [[Biology:Arabian leopard|Arabian leopard]]
* [[Biology:Arabian gazelle|Arabian gazelle]]
* [[Biology:Arabian oryx|Arabian oryx]]
* [[Biology:Arabian red fox|Arabian red fox]]
* [[Biology:Arabian sand gazelle|Arabian sand gazelle]]
* [[Biology:Arabian wildcat|Arabian wildcat]]
* [[Biology:Arabian wolf|Arabian wolf]]
* [[Biology:Arizona bark scorpion|Arizona bark scorpion]]
* [[Biology:Crotalus cerberus|Arizona black rattlesnake]]
* [[Biology:Arizona woodpecker|Arizona woodpecker]]
* [[Biology:Armadillo girdled lizard|Armadillo girdled lizard]]
* [[Biology:Bactrian camel|Bactrian camel]]
* [[Biology:Barbary sheep|Barbary sheep]]
* Bearded dragon
* [[Biology:Big brown bat|Big brown bat]]
* [[Biology:Big free-tailed bat|Big free-tailed bat]]
* [[Biology:Black-tailed jackrabbit|Black-tailed jackrabbit]]
* [[Biology:Blanford's fox|Blanford's fox]]
* [[Biology:Bobcat|Bobcat]]
* [[Biology:Bolson tortoise|Bolson tortoise]]
* Burro
* [[Biology:Cactus wren|Cactus wren]]
* [[Biology:Cactus mouse|Cactus mouse]]
* [[Biology:Cairo spiny mouse|Cairo spiny mouse]]
* [[Biology:California leaf-nosed bat|California leaf-nosed bat]]
* California myotis
* [[Biology:California quail|California quail]]
* Cape ground squirrel
* [[Biology:Cape hare|Cape hare]]
* [[Biology:Caracal|Caracal]]
* Cave myotis
* [[Biology:Cerastes (genus)|Cerastes]]
* [[Biology:Chipmunk|Chipmunk]]
* [[Biology:Chuckwalla|Chuckwalla]]
* [[Biology:Colorado River toad|Colorado River toad]]
* Coues' deer
* Collared peccary
* [[Biology:Scolopendra polymorpha|Common desert centipede]]
* Common genet
* [[Biology:Coyote|Coyote]]
* [[Biology:Cunningham's spiny-tailed skink|Cunningham's spiny-tailed skink]]
* [[Biology:Cuvier's gazelle|Cuvier's gazelle]]
* [[Biology:Desert bighorn sheep|Desert bighorn sheep]]
* [[Biology:Desert box turtle|Desert box turtle]]
* [[Biology:Desert cottontail|Desert cottontail]]
* Desert elephant
* [[Biology:Desert hedgehog|Desert hedgehog]]
* [[Biology:Desert horned lizard|Desert horned lizard]]
* [[Biology:Desert iguana|Desert iguana]]
* [[Biology:Desert kangaroo rat|Desert kangaroo rat]]
* [[Biology:Desert kingsnake|Desert kingsnake]]
* [[Biology:Desert long-eared bat|Desert long-eared bat]]
* Desert monitor
* Desert mule deer
* [[Biology:Desert pipistrelle|Desert pipistrelle]]
* [[Biology:Desert pocket gopher|Desert pocket gopher]]
* [[Biology:Desert tortoise|Desert tortoise]]
* [[Biology:Dorcas gazelle|Dorcas gazelle]]
* Dromedary
* [[Biology:Egyptian mongoose|Egyptian mongoose]]
* [[Biology:Elegant quail|Elegant quail]]
* [[Biology:Fat-tailed gerbil|Fat-tailed gerbil]]
* [[Biology:Fennec fox|Fennec fox]]
* Ferruginous pygmy owl
* [[Biology:Gemsbok|Gemsbok]]
* [[Biology:Gambel's quail|Gambel's quail]]
* [[Biology:Ghost-faced bat|Ghost-faced bat]]
* [[Biology:Scolopendra heros|Giant desert centipede]]
* [[Biology:Gila monster|Gila monster]]
* [[Biology:Gila woodpecker|Gila woodpecker]]
* [[Biology:Grasshopper mouse|Grasshopper mouse]]
* [[Biology:Goanna|Goanna]]
* [[Biology:Golden jackal|Golden jackal]]
* [[Biology:Gopher tortoise|Gopher tortoise]]
* [[Biology:Greater long-nosed bat|Greater long-nosed bat]]
* [[Biology:Greater mouse-tailed bat|Greater mouse-tailed bat]]
* [[Biology:Greater roadrunner|Greater roadrunner]]
* Hamadryas baboon
* [[Biology:Hartebeest|Hartebeest]]
* [[Biology:Honey badger|Honey badger]]
* [[Biology:Hyperolius|Hyperolius]]
* [[Biology:Kangaroo rat|Kangaroo rat]]
* [[Biology:Kit fox|Kit fox]]
* [[Biology:Lappet-faced vulture|Lappet-faced vulture]]
* [[Biology:Lesser long-nosed bat|Lesser long-nosed bat]]
* [[Biology:Lesser mouse-tailed bat|Lesser mouse-tailed bat]]
* [[Biology:Lesser roadrunner|Lesser roadrunner]]
* Libyan jird
* [[Biology:Mauritanian shrew|Mauritanian shrew]]
* [[Biology:Meerkat|Meerkat]]
* [[Biology:Mexican free-tailed bat|Mexican free-tailed bat]]
* [[Biology:Mexican long-tongued bat|Mexican long-tongued bat]]
* [[Biology:Mexican wolf|Mexican wolf]]
* [[Biology:Crotalus scutulatus|Mojave rattlesnake]]
* [[Biology:Nine-banded armadillo|Nine-banded armadillo]]
* [[Biology:North African gerbil|North African gerbil]]
* [[Biology:Northwest African cheetah|Northwest African cheetah]]
* Nubian ibex
* [[Biology:Onager|Onager]]
* [[Biology:Ostrich|Ostrich]]
* Pallid bat
* [[Biology:Pocketed free-tailed bat|Pocketed free-tailed bat]]
* [[Biology:Pygmy gerbil|Pygmy gerbil]]
* [[Biology:Red kangaroo|Red kangaroo]]
* [[Biology:Rhim gazelle|Rhim gazelle]]
* [[Biology:Ring-tailed cat|Ring-tailed cat]]
* [[Biology:Round-tailed ground squirrel|Round-tailed ground squirrel]]
* Rueppell's fox
* [[Biology:Saharan shrew|Saharan shrew]]
* [[Biology:Saharan silver ant|Saharan silver ant]]
* [[Biology:Saharan striped polecat|Saharan striped polecat]]
* [[Biology:Saiga antelope|Saiga antelope]]
* [[Biology:Sand cat|Sand cat]]
* [[Biology:Crotalus cerastes|Sidewinder rattlesnake]]
* [[Biology:Scaled quail|Scaled quail]]
* [[Biology:Scimitar oryx|Scimitar oryx]]
* Silver-haired bat
* [[Biology:Sonoran collared lizard|Sonoran collared lizard]]
* [[Biology:Sonoran Desert tortoise|Sonoran Desert tortoise]]
* [[Biology:Sonoran pronghorn|Sonoran pronghorn]]
* Southwestern myotis
* [[Biology:Crotalus mitchellii|Speckled rattlesnake]]
* Spotted bat
* [[Biology:Spotted hyena|Spotted hyena]]
* [[Biology:Striped hyena|Striped hyena]]
* Texas banded gecko
* [[Biology:Texas horned lizard|Texas horned lizard]]
* Thorny dragon
* [[Biology:Townsend's big-eared bat|Townsend's big-eared bat]]
* [[Biology:Cyclorana platycephala|Water-holding frog]]
* [[Biology:Latrodectus hesperus|Western black widow]]
* [[Biology:Western diamondback rattlesnake|Western diamondback rattlesnake]]
* [[Biology:Western mastiff bat|Western mastiff bat]]
* [[Biology:Western Saharan spiny mouse|Western Saharan spiny mouse]]
* [[Biology:Whitaker's shrew|Whitaker's shrew]]
* White-bellied carpet viper
* Yuma myotis
* [[Biology:Zebra-tailed lizard|Zebra-tailed lizard]]
{{div col end}}

==See also==
* Arid Forest Research Institute (AFRI)
* Chionophile
* Deserts and xeric shrublands
* [[Biology:Xerophile|Xerophile]]
* [[Biology:Xerophyte|Xerophyte]]
{{Clear}}

== References ==
=== Citations ===
{{Reflist|30em}}

=== Sources ===
* {{cite book | publisher = University of Oklahoma Press | isbn = 9780806131467 | editor1-last = Mares | editor1-first = Michael A. | editor2 = Oklahoma Museum of Natural History | title = Deserts | year = 1999 }}

==External links==
*[https://web.archive.org/web/20100114013246/http://environment.nationalgeographic.com/environment/photos/desert-wildlife/ Desert Wildlife Photo Gallery] from ''National Geographic''
*[https://www.flickr.com/photos/lynngagnon/galleries/72157623568321158/ Photo Gallery] from [[Social:Flickr|Flickr]]

[[Category:Xerophiles]]

{{Sourceattribution|Xerocole}}