Countershading, or
ThayerAbbott Handerson Thayer was an American artist, naturalist and teacher. As a painter of portraits, figures, animals and landscapes, he enjoyed a certain prominence during his lifetime, as shown by the fact that his paintings are in the most important U.S. art collections...
's Law, is a form of
camouflageCamouflage is a method of crypsis that allows an otherwise visible organism or object to remain indiscernible from the surrounding environment through deception. Examples include a tiger's stripes and the battledress of a modern soldier...
. Countershading, in which an animal’s pigmentation is darker
dorsallyIn anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
, is often thought to have an adaptive effect of reducing conspicuous shadows cast on the ventral region of an animal’s body. In essence the distribution of light on objects that are lit from above will cause unequal reflection of light on a solid body of uniform colour, such shadows could provide predators with visual cues to a prey's shape and projection.
Countershading, or
ThayerAbbott Handerson Thayer was an American artist, naturalist and teacher. As a painter of portraits, figures, animals and landscapes, he enjoyed a certain prominence during his lifetime, as shown by the fact that his paintings are in the most important U.S. art collections...
's Law, is a form of
camouflageCamouflage is a method of crypsis that allows an otherwise visible organism or object to remain indiscernible from the surrounding environment through deception. Examples include a tiger's stripes and the battledress of a modern soldier...
. Countershading, in which an animal’s pigmentation is darker
dorsallyIn anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
, is often thought to have an adaptive effect of reducing conspicuous shadows cast on the ventral region of an animal’s body. In essence the distribution of light on objects that are lit from above will cause unequal reflection of light on a solid body of uniform colour, such shadows could provide predators with visual cues to a prey's shape and projection. Countershading therefore,
reduces the ease of detection of preyIn ecology, crypsis is the ability of an organism to avoid observation. A form of antipredator adaptation, methods range from camouflage, nocturnality, subterranean lifestyle, transparency, or mimicry...
by potential predators by counterbalancing the effects of shadowing.
Examples
Countershading is observed in a large variety of animals: pronghorn antelope,
White-tailed deerThe white-tailed deer , also known as the Virginia deer, or simply as the whitetail, is a medium-sized deer native to the United States , Canada, Mexico, Central America, and in South America as far south as Peru...
, squirrels,
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, and various lepidopteran larvae.
Alternatively, in many marine animals (including various species of
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
such as
marlinMarlin, Istiophoridae, is a "billfish" and is closely linked to freshwater trout. A marlin has an elongated body, a spear-like snout or bill, and a long rigid dorsal fin, which extends forward to form a crest. Its common name is thought to derive from its resemblance to a sailor's marlinspike...
s and
sharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs....
s, penguins and
cephalopod{Taxobox| name = Cephalopods| fossil_range = | image = Tafel 054 300.jpg| image_caption = A variety of cephalopod forms from Ernst Haeckel's 1904 Kunstformen der Natur| regnum = Animalia| image_width = 220px| phylum = Mollusca| classis = Cephalopoda...
s) this form of camouflage may work through background matching; when seen from the top, the darker
dorsalIn anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
area of the animal blends into the darkness of the water below, when seen from below, the lighter ventral area blends into the sunlight from the surface.
Furthermore, countershading could also result from differential selection pressures on dorsal and ventral surfaces, from the need to protect against the damaging properties of UV light or
abrasionIn dermatology, an abrasion is a wound caused by superficial damage to the skin, no deeper than the epidermis. It is less severe than a laceration, and bleeding, if present, is minimal. Mild abrasions, also known as grazes or scrapes, do not scar or bleed, but deep abrasions may lead to the...
.
History
Abbott Handerson ThayerAbbott Handerson Thayer was an American artist, naturalist and teacher. As a painter of portraits, figures, animals and landscapes, he enjoyed a certain prominence during his lifetime, as shown by the fact that his paintings are in the most important U.S. art collections...
was one of the first to conduct extensive research on and to write about certain aspects of protective colouration in nature. In 1892, he wrote about the function of countershading in nature, in which he accounted for the white undersides of animals. For this reason countershading is sometimes called Thayer’s Law.
Military camouflageMilitary camouflage became an essential part of modern military tactics after the increase in accuracy and rate of fire of weapons during the 19th century. Until the 20th century armies tended to use bright colors and bold, impressive designs. These were thought to daunt the enemy, foster unit...
sometimes uses the same principle; Thayer even obtained a patent in 1902 to paint warships using a countershaded scheme.
See also
- Synodontis nigriventris, an "upside-down" catfish (with reverse countershading)
- counterchanging, a heraldic device of similar appearance