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Snow camouflage is the use of a different coloration or pattern for effective camouflage in summer and winter. Summer patterns are typically disruptively patterned combinations of shades of browns and greys, up to black, while winter patterns are dominated by white to match snowy landscapes.
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Among animals, snow camouflage is a type of seasonal polyphenism with a distinct winter plumage or pelage. It is found in birds such as the rock ptarmigan, lagomorphs such as the Arctic hare, mustelids such as the stoat, and one canid, the Arctic fox. Since these have evolved separately, the similar appearance is due to convergent evolution.
In military usage, soldiers often either exchange their disruptively-patterned summer uniforms for thicker snow camouflage uniforms printed with mainly-white versions of camouflage patterns in winter, or they wear white overalls over their uniforms. Vehicles and guns are often simply repainted in white. Occasionally, aircraft too are repainted in snow camouflage patterns.
Among animals
Animals of the far north, like the showshoe and Arctic hares, Arctic fox, stoat, and rock ptarmigan change their coat colour (by moulting and growing new fur or feathers) from brown or grey summer camouflage to white in the winter; the Arctic fox is the only species in the dog family to do so. However, Arctic hares which live in the far north of Canada, where summer is very short, remain white year-round. Since these animals in widely separated groups have evolved separately, the similarity of coloration is due to convergent evolution, on the presumption that natural selection favours a particular coloration in a particular environment.
The seasonal polyphenism in willow grouse differs between Scottish and Scandinavian populations. In Scotland, grouse have two plumages (breeding and non-breeding), while in Scandinavia there is a third plumage, a white winter morph. The genetic basis for this is not in the melanin pigment system, and is probably due to regulatory changes. The behaviour of moulting females in springtime depends on their plumage state: they tend to sit on snow while they are mainly white, but choose the border between bare ground and snow when they have more dark feathers. They seem to be choosing the best compromise between camouflage and food quality.
Climate change from global warming is leading to a mismatch between the seasonal coat coloration of arctic animals such as snowshoe hares with the increasingly snow-free landscape.
Military usage
The principle of varying coloration with the changing seasons has military applications.
Second World War
Several armies in the Second World War in Northern European countries preferred separate winter uniforms rather than oversuits. The Waffen-SS went a step further, developing reversible uniforms with separate schemes for summer and autumn, as well as white winter oversuits. Other German units fighting in Eastern Europe were at first poorly equipped for winter, having to make do with ordinary summer uniforms, but in the winter of 1942 to 1942 new white two-piece hooded oversuits with long mitten gauntlets started to arrive. American troops in Europe in the winter of 1944 to 1945 improvised snow capes and helmet covers from white cloth such as bed linen.
The Red Army issued a report, "Tactical and Technical trends, No. 17" in January 1943 on the camouflage of tanks in winter. It advised either all-white using zinc white or titanium white paint for level, open country, or disruptive two-colour winter camouflage for areas with more variety including "forests, underbrush, small settlements, thawed patches of earth". The two colours could be achieved either by leaving around a quarter to a third of the vehicle's summer camouflage uncovered, or by repainting the whole vehicle in white with dark gray or gray-brown spots. Units were advised not to paint all their vehicles identically, but to have some tanks all white, some in white with green stripes, and some in white and gray or gray-brown. Winter camouflage was not limited to paint: tracks left in the snow were to be obliterated, vehicles parked in cover, headlights covered with white fabric, shelters constructed, or else vehicles covered with white fabric, or dark fabric scattered with snow.
Post-war
Later in the 20th century, as disruptively patterned uniforms became widespread, winter variants of patterns such as Flecktarn were developed, the background colour (such as green) being replaced with white to form a Schneetarn (snow camouflage pattern). Aircraft deployed in winter have sometimes been snow camouflaged, as with Sepecat Jaguars on exercise in Norway.
Snow camouflage is manufactured commercially for use by hunters by companies such as Hyperstealth, Kingsnow, Mossy Oak, Naked North, NaturalGear, Realtree, and True Timber; some have been adopted by military and law enforcement units. For example, NaturalGear derive their patterns from photographic images using "the colors of nature".