Editing Camouflage (section)

=== Changeable skin coloration ===

{{further|Active camouflage|Snow camouflage}}

Animals such as [[chameleon]], frog,{{sfn|Cott|1940|pages=30–31}} flatfish such as the [[peacock flounder]], squid, octopus and even the isopod [[idotea balthica]] actively change their skin patterns and colours using special [[chromatophore]] cells to resemble their current background, or, as in most chameleons, for [[Signalling theory|signalling]].{{sfn|Forbes|2009|pages=52, 236}} However, [[Smith's dwarf chameleon]] does use active colour change for camouflage.<ref>{{cite journal |last1=Stuart-Fox |first1=Devi |last2=Moussalli |first2=Adnan |last3=Whiting |first3=Martin J. |title=Predator-specific camouflage in chameleons |journal=Biology Letters |date=23 August 2008 |volume=4 |issue=4 |pages=326–9 |doi=10.1098/rsbl.2008.0173 |pmid=18492645 |pmc=2610148 }}</ref>

{{multiple image
|total_width=400px
|align=left
|image1=Peacock Flounder Bothus mancus in Kona.jpg
|caption1=Four frames of the same [[peacock flounder]] taken a few minutes apart, showing its ability to match its coloration to the environment
|image2=Melanophores with dispersed or aggregated melanosomes.svg
|caption2=Fish and frog melanophore cells change colour by moving pigment-containing bodies.
}}

Each chromatophore contains pigment of only one colour. In fish and frogs, colour change is mediated by a type of chromatophore known as [[melanophore]]s that contain dark pigment. A melanophore is star-shaped; it contains many small pigmented [[organelle]]s which can be dispersed throughout the cell, or aggregated near its centre. When the pigmented organelles are dispersed, the cell makes a patch of the animal's skin appear dark; when they are aggregated, most of the cell, and the animal's skin, appears light. In frogs, the change is controlled relatively slowly, mainly by [[hormone]]s. In fish, the change is controlled by the brain, which sends signals directly to the chromatophores, as well as producing hormones.<ref name="Wallin">{{cite journal |last=Wallin |first=M. |url=http://www.bioscience-explained.org/ENvol1_2/pdf/paletteEN.pdf |archive-url=https://web.archive.org/web/20110722083738/http://www.bioscience-explained.org/ENvol1_2/pdf/paletteEN.pdf |archive-date=2011-07-22 |url-status=live |title=Nature's Palette |journal=Bioscience Explained |year=2002 |access-date=17 November 2011 |volume=1 |issue=2 |pages=1–12}}</ref>

The skins of cephalopods such as the octopus contain complex units, each consisting of a chromatophore with surrounding muscle and nerve cells.{{sfn|Cott|1940|page=32}} The cephalopod chromatophore has all its pigment grains in a small elastic sac, which can be stretched or allowed to relax under the control of the brain to vary its opacity. By controlling chromatophores of different colours, cephalopods can rapidly change their skin patterns and colours.<ref name="Cloney">{{cite journal |title=Ultrastructure of Cephalopod Chromatophore Organs |author1=Cloney, R. A. |author2=Florey, E. |journal=Zeitschrift für Zellforschung und Mikroskopische Anatomie |volume=89 |issue=2 |pages=250–280 |year=1968 |pmid=5700268 |doi=10.1007/BF00347297|s2cid=26566732 }}</ref><ref>{{cite web |url=http://marinebio.org/species.asp?id=553 |title=Day Octopuses, Octopus cyanea |publisher=MarineBio Conservation Society |access-date=31 January 2013 |archive-url=https://web.archive.org/web/20160320205031/http://marinebio.org/species.asp?id=553 |archive-date=20 March 2016 |url-status=dead }}</ref>

On a longer timescale, animals like the [[Arctic hare]], [[Arctic fox]], [[stoat]], and [[rock ptarmigan]] have [[snow camouflage]], changing their coat colour (by moulting and growing new fur or feathers) from brown or grey in the summer to white in the winter; the Arctic fox is the only species in the [[Canidae|dog family]] to do so.<ref name="Churchill">{{cite web |url=http://churchillpolarbears.org/churchill/arctic-wildlife |title=Arctic Wildlife |publisher=Churchill Polar Bears |year=2011 |access-date=22 December 2011}}</ref> However, Arctic hares which live in the far north of [[Canada]], where summer is very short, remain white year-round.<ref name="Churchill"/><ref name="ParksCanada">{{cite book |title=The Status of Arctic Hare (Lepus arcticus bangsii) in Insular Newfoundland |url=http://www.env.gov.nl.ca/env/wildlife/endangeredspecies/ssac/arctic_hare.pdf |publisher=Newfoundland Labrador Department of Environment and Conservation |last=Hearn |first=Brian |date=20 February 2012 |access-date=3 February 2013 |page=7 |archive-url=https://web.archive.org/web/20160304200851/http://www.env.gov.nl.ca/env/wildlife/endangeredspecies/ssac/arctic_hare.pdf |archive-date=4 March 2016 |url-status=dead }}</ref>

The principle of varying coloration either rapidly or with the changing seasons has military applications. ''[[Active camouflage]]'' could in theory make use of both dynamic colour change and counterillumination. Simple methods such as changing uniforms and repainting vehicles for winter have been in use since World War II. In 2011, [[BAE Systems]] announced their [[Adaptiv]] infrared camouflage technology. It uses about 1,000 hexagonal panels to cover the sides of a tank. The [[Peltier plate]] panels are heated and cooled to match either the vehicle's surroundings (crypsis), or an object such as a car (mimesis), when viewed in infrared.<ref>{{Cite news |url=https://www.bbc.co.uk/news/technology-14788009 |journal=BBC News |title=Tanks test infrared invisibility cloak |date=5 September 2011 |access-date=13 June 2012}}</ref><ref name=Adaptiv-Cloak>{{cite web |url=http://www.baesystems.com/en/feature/adativ-cloak-of-invisibility |title=Adaptiv – A Cloak of Invisibility |publisher=BAE Systems |year=2011 |access-date=14 November 2015}}</ref><ref>{{cite web |url=http://www.baesystems.com/en/feature/adativ-cloak-of-invisibility#! |title=Innovation Adaptiv Car Signature |publisher=BAE Systems |year=2012 |access-date=14 November 2015}}</ref>

<gallery class="center" mode="nolines" heights="150px" widths="150px">
File:Rock Ptarmigan (Lagopus Muta).jpg|Rock ptarmigan, changing colour in springtime. The male is still mostly in winter plumage
File:Norwegian Winter War Volunteers.jpg|Norwegian volunteer soldiers in [[Winter War]], 1940, with white camouflage overalls over their uniforms
File:Arctic Hare.jpg|Arctic hares in the low arctic change from brown to white in winter
File:Bundesarchiv Bild 101III-Roth-173-01, Russland, Raum Charkow, Jagdpanzer.jpg|Snow-camouflaged German [[Marder III]] [[jagdpanzer]] and white-overalled crew and infantry in Russia, 1943
File:Yemen Chameleon (cropped).jpg|[[Veiled chameleon]], ''Chamaeleo calyptratus'', changes colour mainly in relation to mood and for signalling.
File:Adaptiv infrared camouflage demo hiding tank as car.jpg|[[Adaptiv]] infrared camouflage lets an armoured vehicle mimic a car.
</gallery>