Camouflage , also known as crypsis in behavioral biology (from ancient Greek κρύψις krýpsis , German 'to hide, to hide' ), is the process or condition in animals that aims to send misleading signals to another living being. It is both the simplest and most effective mechanism for reducing the risk of predation and a possible evolutionary adaptation of predators , which, due to their camouflage, are less easily perceived by potential prey. This deception can be directed against all sensory organs, for example, deceive visual perception (“the eye ”), auditory perception (“the ear ”) or olfactory perception (“the olfactory sense ”). As a special form of camouflage certain to mimicry variants be construed, where, for example savory or defenseless species exterior features copy bad tasting or fortified species and thus to potential predators disguise.
If the visual (the externally visible) appearance of an animal is used for camouflage, experts refer to this appearance as camouflage .
The exchange of signals is an essential prerequisite for any communication and requires at least one transmitter and one receiver of signals. Camouflage in animals can therefore be described as an ability acquired in the course of tribal history to only send signals, at least under certain circumstances, that differ as little as possible from the circumstances surrounding the individual. Camouflage can serve both to hide from predators and to hide from potential prey ( attack camouflage ).
Somatolysis (from ancient Greek σῶμα sōma , German 'body' and λύσις lýsis , German 'dissolution' , literally dissolution of the body ) describes the merging of a living being with its natural environment through a specially patterned and sometimes color-coordinated costume - the animal becomes invisible to a certain extent by adapting to the structure and color of its surroundings.
This form of camouflage is mostly used to evade natural enemies or, for example, with lions (a hunter) and other big cats, to be discovered by their potential prey as late as possible. Conversely, a hunting lioness can hardly be distinguished from the steppe grasses, which are also brown in dry periods, even at close range due to their brown fur. The same applies to many other cats, such as the cheetah and the leopard .
With somatolysis, from the point of view of the observing person, the pattern and color tone can appear very noticeable instead of camouflaging and thus seem counterproductive. An example of this is the black and white striped zebra . In the permanent exhibition of the Berlin Museum of Natural History , the development of fur coloring is described as follows:
“The habitat of the tsetse fly is the tropical belt of Africa, south of the Sahara . During the spread on the African continent, the dark colored wild horses from Asia crossed this area. A striped pattern was a selective advantage here, because the complex eyes of the mostly nocturnal fly could not dissolve the silhouette of the zebra in the dark. The zebra stripes were used to camouflage themselves from the disease carrier. The quagga, on the other hand, which was exterminated 100 years ago , was a zebra whose stripe pattern was limited to the base of the tail, the head and the neck, without any disadvantage. Its - striped - ancestors had passed through the habitat of the tsetse fly and left it again in the south. In their new habitat, the Cape Province , the stripe pattern no longer offered a selective advantage and could be abandoned like with the quagga. "
This interpretation was confirmed in two studies in 2012 and 2014. Was in 2019 - based painted replicas of human body - were further evidence that horseflies are attracted by brown models ten times more than black models with white stripes. Beige painted models attracted horseflies twice as often as black and white striped ones. The cause of these differences is evidently that the stripes lead to considerable irritation during landing when braking and therefore the landing does not occur more frequently than with non-striated targets. Previously it was thought that - for example, from the perspective of a crouch on the floor roving Löwin - the vertical side, of the head and abdomen more horizontal strip of a ground-level closely packed stationary herd visually with the tall grass and the buzz of day often heated Air unite and the contours of the individual animal dissolve, which makes it difficult for the predator to fixate a certain animal.
A well-known example of color-camouflaged animals is also the (white) polar bear , which is excellently camouflaged against potential prey when hunting young (white) harp seals , and vice versa, the baby seals in snow and ice cannot be distinguished from the ground from a greater distance and thus are protected from being discovered too quickly. The same applies to certain animal lice from the Ischnocera group : US researchers reported in 2010 that white-skinned lice can be detected in the plumage of white-feathered birds and dark-skinned lice in the plumage of dark-feathered birds; apparently it was the picking behavior of the cleaning hosts that caused a selection pressure towards the predominance of a certain color variant in the ectoparasites . The snowy owl, too, only looks very conspicuous in the aviary of a zoo due to its brilliant white plumage speckled with brown spots. On the other hand, sitting in leaves that are slightly covered with snow, it can hardly be distinguished from its surroundings.
In mid-2006, a research group from the University of Freiburg reported on an experiment with sometimes conspicuously colored butterfly dummies , which they had placed on different tree trunks - always with dead mealworms . After a certain period of time, checks were carried out to determine whether the mealworm had disappeared, which was rated as 'moth eaten'. Result: The moth dummies that were patterned on the wing edges 'survived' the longest; Mealworms disappeared significantly more often from the dummies patterned inside the wing. This was true even for blue-pink colored mock-ups on a moss-covered oak. From their observations, the researchers concluded that the disintegration of the body contours through spotted wing edges means that the innate trigger mechanisms of potential predators no longer detect the camouflaged butterfly as 'prey', regardless of the surface. By staining the inside of the wing, a butterfly can only camouflage itself depending on the suitably colored background.
- Further examples
- Trembling spiders can set their web to vibrate quickly, so that, due to these movements, they can no longer be reliably located by a predator in the web.
- Near the beach you can often see fish whose basic color appears silvery, but which have distinctive, dark stripes on the sides - from the back to the belly. When the sun is shining in the shallow water, even as a snorkeling layman, you can notice that the shadows on the bottom of the undulating water surface create comparable stripe patterns. Viewed from the side or at an angle from above, such fish can hardly be distinguished from their surroundings even from a short distance.
- Many conspicuously red-colored fish that can be found in coral reefs , for example , have developed this coloration that is conspicuous at first glance, because they are better protected from predatory fish in the dark: the red light is most strongly filtered off by the water (this is why water appears in the Depth always bluish), so that these fish appear blue-gray in the dark.
- Some jellyfish and shrimp are as translucent as water.
- The caterpillars of some butterflies , which are green like a leaf, are no less well known .
- Among the most well-camouflaged birds include bitterns . Their back plumage is predominantly brown, while their front is pale and has dotted, horizontal stripes. Thanks to this somatolytic coloration of the throat and chest, these large birds cannot be made out even behind a few reeds. The camouflaging coloring of the plumage is supported by behavioral components. Bitterns move extremely slowly through the reeds. In the event of danger, turn your front towards the source of danger, as it is better camouflaged. If the source of danger changes its position, the bittons also turn. Bitterns adopt a typical rigid posture when in danger, with the neck stretched out and the beak pointing towards the sky. They can hold this position for hours. If the wind moves the reeds, the bitterns sway with the wind movements.
- Many birds have spotted eggs: such eggs stand out less from the nest than unspotted eggs. In the case of the great tit , British researchers have also shown that the thinner the eggshell, the denser the reddish speckles. Apparently, the reddish color pigments act like a kind of additional glue between the calcite crystals of the shell.
- The small plover of the genus Charadrius have a contrasting colored plumage with a white and often a black collar. As a result, no bird silhouette is recognized at a cursory glance, but the head and torso are perceived as two different objects (stones).
Chirping insect in the high June grass
Cicada on tree trunk
Jumping spider with prey
Snowshoe hare in white winter fur
Under melanism is understood a particularly pronounced storage of dark pigments (especially of melanin ) in the skin. At the end of the 19th century there was such a drastic change in the appearance of the birch moth in English industrial areas that the term “industrial melanism” became established.
The term assumes a change in the frequency distribution of light and dark variants of the butterfly as a result of air pollution by industrial companies. However, this interpretation is controversial today.
In contrast to many animals living on the ground, which move on the surface of the earth and thus in a two-dimensional habitat , flying animals, water or tree dwellers stay in a three-dimensional habitat. Such animals are potentially exposed to attack not only from the sides and above, but also from below. The fact that the light always falls from above on the body does not allow a uniform color for the purpose of camouflage: uniformly dark animals would be clearly visible from below against the bright sky, uniformly light animals from above against the dark background. The adaptation developed several times independently of one another in the course of the tribal history of different groups is counter- shading ( engl. Countershading ). So many fish are belly-sided colored much brighter than on its upper side and similarly take advantage of many birds and mammals that kind of camouflage.
Adaptation to ambient brightness
Some marine animals in the middle water depth imitate the brightness of the environment and give off a faint shimmer downwards in order to cover their shadow, e.g. B. the lesser black dogfish ( Etmopterus spinax ). Hormonally controlled, the finely distributed luminous dots can be actively shielded in stages by variable chromatophores and adapted very precisely to the ambient brightness.
The dwarf squid Euprymna scolopes uses endosymbionts to generate the shimmer of light : luminous bacteria live in its coat , so that the host - potential predators swimming under it - can hardly be noticed. The squid can actively adjust the amount of light to the ambient brightness; its nervous system perceives the brightness generated by the bacteria directly (i.e. not only through the eyes).
The ability to change body color to match the environment as closely as possible is often a protective device and was developed independently by a wide variety of animal species . The most famous and almost proverbial for people who know how to adapt to any environment are the chameleons . Chameleons also move extremely slowly and rock back and forth when moving forward, so that they can hardly be perceived in the branches of a tree that is moved by the wind.
The mountain hare who u. a. lives in Northern Europe and the Alpine region , its coat changes over the course of the year: in summer it is gray-brown in color, while its winter coat is white. The ermine changes its coat color and the Ptarmigan its plumage in such a striking way during the year .
Many octopuses and squids can change the color of their skin in a matter of seconds. The long-sleeved octopus Macrotritopus defilippi , for example, camouflages itself on the sea floor by mimicking the color, body shape and movement of the peacock's butt Bothus lunatus . Also Sepia officinalis can with yellow, orange red and dark brown chromatophores camouflage. The animal evaluates the brightness contrasts of the background with a single type of receptor in its eye (at 492 nm wavelength). These animals also have another, effective protective mechanism that earned them the nickname octopus : cornered by a predator, they can splash a dark liquid into the water behind them, which forms a cloud that is so thick that it becomes real because of this camouflage Chances of escaping.
- Further examples
- The mutable crab spider (Misumena vatia) is often found in the yellow flowers of marsh marigolds , but occasionally also in the white flowers of the bindweed , where insects lie in wait . Sexually mature females can store a yellow dye in their otherwise white skin and break it down again. They can change color within hours and are then hardly visible to the human eye in a correspondingly colored flower.
- The antennae Antennarius commersoni , one of the so-called frogfish , also has two to four main color states, between which it can sometimes switch within seconds and sometimes only in the course of hours. These animals often sit motionless and color-matched on the ground, looking like an overgrown rock due to their warty-bulging body surface. The only noticeable thing is an imitation fish that hangs from a thread-like protuberance of the foremost dorsal fin and attracts predatory fish, which are then eaten by this "living stone" itself.
- Another relatively well-known example are plaice and other flatfish such as pheasant butt ( Bothus mancus ), which can change the color and pattern of their body surface according to the ground on which they lie: their skin looks more blotchy on gravel than on sand. Various color cells are embedded in their skin (chromatophores), which expand (then their surface is large and colored), but can also contract if necessary (their surface is then minimal). The desired pattern is ultimately caused by the distribution of different types of color cells on the skin and controlled by the eye.
- The larva (caterpillar) of the tomato swarm Manduca quinquemaculata (in the English-speaking world: Tomato hornworm ) is also called the tomato caterpillar and is considered to be an important pest. Depending on the ambient temperature, it can change its color: if the temperature is constantly above 28 degrees Celsius, the caterpillars are green, at lower temperatures the caterpillars are almost black. Scientists attribute this to the fact that certain hormones are active in the juvenile caterpillars depending on the outside temperature; They interpret the biological benefit as follows: At high temperatures, the advantage of camouflage prevails, at lower temperatures (especially in autumn) the advantage of better absorption of solar heat in the plants, which are then at least partially dried up, predominates .
- Central American bark bugs (Aradidae) quickly darken on contact with water: Even after a thunderstorm, they retain the color of the tree bark on which they are located and which is also significantly darker when it rains than when it is dry.
Not quite clean delineated against the Somatolyse is the mimesis , which can also be regarded as a form of camouflage. While somatolysis covers all cases that aim at becoming invisible, animals remain visible with mimetics, but can easily be confused with things in their environment due to their body color and build. With regard to their body color, animals may also imitate the environment when performing mimetics, but their body color, unlike when changing color, is permanent. One example is the blackberry leaf tensioner - it looks like bird droppings.
A well-known example are the anemonefish : They live in sea anemones without being sted by them. They do this by taking certain chemical substances from the sea anemone as protective substances. The sea anemone can then no longer distinguish the fish from its own tentacles. If the protective substances on the scales of the fish are removed in the experiment, the anemonefish will also be nettled.
At the beginning of the 1990s, a project on the subject of chemical camouflage was financed at the University of Bayreuth . a. was about increasing reproductive success through camouflage. The project report stated that the reproductive success of aphid parasitoids is optimized by chemical camouflage when these parasites attack aphid colonies that are invaded by ants ; Ants use the sweet excretions of aphids as a source of food. It is important here that ants remove predatory and parasitic aphid antagonists from the aphid colony. Certain parasitoids are, however, adapted to these protective activities of the ants in favor of the aphids through chemical camouflage: They are not detected by the ants and can develop undisturbed at the aphid's expense.
The blue gentian lays its eggs preferentially on leaves of the gentian lung , where they develop into caterpillars . The caterpillars are often carried by red garden ants in their colonies and looked after like their own young animals. Danish researchers reported in early 2008 that this form of social parasitism was based on the caterpillars being protected from exposure by chemical substances in their skin.
Other forms of chemical camouflage are used against ants . Many invertebrates mimic the pheromones that ants use to mark roads. The ants follow this wrong road and run straight to their enemies. Some arachnids, species of millipedes, and beetles specifically mimic the pheromones found in ant larvae. In this way they can enter the burrow to the brood chambers without hindrance and use the larvae.
Sound utterances are much more difficult to analyze than visual features, since this can usually only be achieved with considerable technical effort - especially outdoors. Therefore, clear findings are so far rare.
A long-tailed cat was observed in the jungle of the Amazon basin imitating the call of young two-color tamarins, whereupon adult two-color tamarins approached the location of these calls. This in turn meant that the wildcat tried to capture one of the approaching marmosets.
The blue gentian ant ( Maculinea rebeli ) lays its eggs exclusively on the gentian . When the caterpillars that have emerged from the eggs have eaten fat on the gentian, they drop to the ground and then suddenly smell like queens of the ant species Myrmicaschencki . The ants then carry them into the ant nest and feed them there. This chemical camouflage had been known for a long time, and in 2008 British researchers also analyzed the sounds made by ants and caterpillars. They found that caterpillars in the ant nest make sounds that are very similar to the sounds of the queen ants. If the ants workers were played the sounds of their queen and the sounds of the caterpillars, they teased the loudspeaker equally in both cases.
In the case of butterflies from the bear moth family , it has been shown that a tasty species mimics the sounds of an unpalatable species and therefore both species are not eaten by bats.
The skull hawk can produce a chirping sound with its trunk that resembles the sounds of a queen bee . This enables him to gain access to the beehive, where he can then suck the honey out of the honeycomb with the help of his long trunk.
Those hover flies that look like wasps also make flight noises similar to those of wasps. This is mainly due to the extremely similar frequency of the wing beats: 147 wing beats per second were detected in hover flies and 150 in wasps.
Other forms of camouflage
- Some species of butterflies camouflage their head (and thus their potential direction of flight) with a feeler-like extension of their abdomen.
- The Asian lacquer scale louse Tachardia lacca colonizes u. a. Trees of the genus Ficus . They drill into leaves, suck out sap and then excrete a resinous secretion that covers their bodies, camouflaging them as an apparent part of the tree.
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