Deception in animals
Deception in animals is the transmission of misinformation by one animal to another, of the same or different species, in a way that propagates beliefs that are not true. Deception in animals does not automatically imply a conscious act, but can occur at different levels of cognitive ability.
Mimicry and camouflage enable animals to appear to be other than they are. Prey animals may appear as predators, or vice versa; both predators and prey may be hard to see (crypsis), or may be mistaken for other objects (mimesis). In Batesian mimicry, harmless animals may appear to be distasteful or poisonous. In automimicry, animals may have eyespots in less important parts of the body than the head, helping to distract attack and increase the chance of survival.
More actively, animals may feign death when they detect a predator, or may quickly conceal themselves or take action to distract a predator, such as when a cephalopod releases ink. In deimatic behaviour, a harmless animal adopts a threatening pose or displays startling, brightly coloured parts of its body to startle a predator or rival.
Some animals may use tactical deception, with behaviour that is deployed in a way that other animals misinterpret what is happening to the advantage of the agent. Some of the evidence for this is anecdotal, but in the great apes in particular, experimental studies in ethology suggest that deception is actively practised by some animals.
- 1 Overview
- 2 Mimicry
- 3 Camouflage
- 4 Feigning death
- 5 Concealment
- 6 Distraction displays
- 7 Deimatic displays
- 8 Tactical deception
- 9 See also
- 10 References
- 11 Further reading
Some types of deception in animals are completely involuntary (e.g. disruptive colouration), but others are under voluntary control and may involve an element of learning. Most instances of voluntary deception in animals involve a simple behaviour, such as a cat arching its back and raising its hackles, to make itself appear larger than normal when attacked. There are relatively few examples of animal behaviour which might be attributed to the manipulative type of deception which we know occurs in humans, i.e. "tactical deception". It has been argued that true deception assumes the deceiver knows that (1) other animals have minds, (2) different animals' minds can believe different things are true (when only one of these is actually true), and (3) it can make another mind believe that something false is actually true. True deception requires the deceiver to have the mental capacity to assess different representations of reality. Animal behaviour scientists are therefore wary of interpreting a single instance of behaviour to true deception, and explain it with simpler mental processes such as learned associations. In contrast, human activities such as military deception are certainly intentional, even when they involve methods such as camouflage which physically parallel camouflage methods used by animals.
Levels of deception in animals
Mitchell and Thompson list four levels of deception in animals:
- false markings on animals, such as butterfly markings that indicate their heads are at the back end of their bodies as an aid to escape, or markings to make predators appear safe
- false behaviour, such as a predator acting in a way to hide its predatory nature around prey
- Feigned injury to get or divert attention; for example, a parent bird feigning a broken wing to attract a predator away from its defenceless offspring
- Verbal deception such as a chimp misleading other chimps to hide a food source, or a human lying in order to deceive another
Mimicry is the similarity of one species to another which protects one or both species. This similarity can be in appearance, behaviour, sound, scent, and location, with the mimics found in similar places to their models. There are many forms of mimicry, and an individual example may fall into more than one of the recognised categories.
Defensive or protective mimicry takes place when organisms are able to avoid encounters that would be harmful to them by deceiving enemies into treating them as something else.
Batesian mimicry is a form of mimicry typified by a situation where a harmless species has evolved to imitate the warning signals of a harmful species directed at a common predator. The harmful species (the model) might have spines, stingers, or toxic chemistry, while its apparent double has no defence other than resembling the unpalatable species. Protection of the mimic from predators is afforded by its resemblance to the unpalatable species, which the predator associates with a certain appearance and a bad experience.
Examples of Batesian mimicry are the several species of butterflies that mimic the toxic Heliconid butterflies. Another butterfly mimic is the non-toxic great Mormon of Indonesia. Each female butterfly (regardless of her colouration) can produce one or more different female forms which mimic any of five other species of foul-tasting butterflies. Batesian mimicry is also found in venomous coral snakes and the harmless milk snake. Both snakes are marked with alternating yellow, red, and black bands, causing potential predators to avoid both. The snakes can often be distinguished by using an old saying: "Red against yellow: kill a fellow. red against black: friend to Jack." The deadly coral snake has bands in the order of red, yellow, black, while the innocuous species have the pattern of red, black, yellow (although there are exceptions).
Deception by Batesian mimicry need not involve visual mimicry, but can be deception of any of the senses. For example, some moths use a highly effective defence against bats. In response to hearing ultrasound emitted by hunting bats, they produce loud ultrasonic clicks to mimic the unpalatable tiger moth – a case of auditory Batesian mimicry.
Müllerian mimicry occurs when two or more poisonous species, that may or may not be closely related and share one or more common predators, have come to mimic each other's warning signals.
For example, the viceroy butterfly appears very similar to the noxious-tasting monarch butterfly. Although it was for a long time purported to be an example of Batesian mimicry, the viceroy has recently been discovered to be just as unpalatable as the monarch, making this a case of Müllerian mimicry. Poison dart frogs of South America and Mantella frogs of Madagascar are examples of Müllerian mimicry with their conspicuous colouration (bright colours against black markings) and toxic composition.
Müllerian mimicry may also use any of the senses. For example, many snakes share the same auditory warning signals.
Aggressive mimicry describes predators (or parasites) which share the same characteristics as a harmless species, allowing them to avoid detection by their prey (or host).
Anglerfish are named for their characteristic method of predation. Anglerfish typically have at least one long filament (the illicium) sprouting from the middle of the head, protruding above the fish's eyes and terminating in an irregular growth of flesh (the esca) at the tip of the filament. The filament is moveable in all directions and the esca can be wiggled so as to resemble a prey animal, thus acting as bait to lure other predators close enough for the anglerfish to devour them whole. Some deep-sea anglerfishes of the bathypelagic zone emit light from their escas to attract prey. This bioluminescence is a result of symbiosis with bacteria.
Another example of aggressive mimicry is where males are lured towards what would seem to be a sexually receptive female only to be eaten. Studies on female fireflies of the genus Photuris revealed they emit the same light signals that females of the genus Photinus use as a mating signal. Further research showed male fireflies from several different genera are attracted to these "femmes fatales", and are subsequently captured and eaten. Female signals are based on that received from the male, each female having a repertoire of signals matching the delay and duration of the female of the corresponding species.
Aggressive mimicry need not involve the sense of vision. The assassin bug preys on spiders, entering their web and plucking its silk threads until the spider approaches. This vibrational aggressive mimicry matches a general pattern of vibrations which spiders treat as prey, having a similar temporal structure and amplitude to leg and body movements of typical prey caught in the web.
Automimicry, or intraspecific mimicry, is when animals have one body part that mimics another to increase survival during an attack, or helps predators appear innocuous.
Many moth, butterfly, and fish species have "eye-spots": large dark markings that help prey escape by deceiving predators to attack a false target, such as the gray hairstreak (Strymon melinus), that shows the false head at the rear, held upwards at rest. An animal has a better chance of surviving an attack to the outer part of its body than an attack to the head.
Another example of automimicry is the "two-headed" snake of Central Africa which has a tail that resembles a head and a head that resembles a tail. The snake even moves its tail in the way most snakes move their heads. This adaptation functions to deceive prey as to where the attack is originating from.
Camouflage is the use of any combination of materials, colouration, or illumination for concealment, by making animals difficult to see (crypsis), or by disguising them as something else (mimesis). This can be as simple as having green skin or pelage colouration for a background of foliage, a nest whose shape, emissions and entries are all disguised by local materials (dirt, twigs, stones, etc.), or as complex as an animal actively changing its appearance according to the changing background.
There are several methods of achieving crypsis. These include, resemblance to the surroundings, disruptive colouration, eliminating shadow, self-decoration, cryptic behaviour, motion camouflage, changeable skin appearance, countershading, counter-illumination, transparency, and silvering to reflect the environment.
There are many examples of species which are cryptically coloured to resemble their surroundings. For example, Uroplatus geckos can be almost completely invisible, even to a nearby observer. Similarly, the katydids, a group of grasshopper-like insects found worldwide, are nocturnal and use their cryptic colouration to remain unnoticed during the day. They remain perfectly still, often in a position that increases the effectiveness of their camouflage.
Some animals have disruptive colouration in which their colours or patterning appear highly conspicuous when outside their normal environment but highly cryptic when in it. For example, the blue Morpho, a forest butterfly, has iridescent blue upper wings and a 17 cm wingspan. However, because the underwings are dark, when the Morpho flies through the flickering light of the forest or even out in daylight, it seems to disappear. Other forest species, especially mammals, use disruptive colouration and have spotted or striped pelage which helps break up the animal's outline. In the shade created by trees or other foliage, even large mammals such as leopards, jaguars, ocelots, and okapi are difficult to see because of such disruptive colouration.
Underwater animals adopt a wide range of methods of camouflage including transparency, reflection, counter-illumination, countershading, self-decoration, and others.
Most forms of camouflage are ineffective when the camouflaged animal moves because the motion is easily seen by the observing predator or prey. However, insects such as hoverflies and dragonflies use motion camouflage: the hoverflies to approach possible mates, and the dragonflies to approach rivals when defending territories. Motion camouflage is achieved by moving so as to stay on a straight line between the target and a fixed point in the landscape; the pursuer thus deceives the target animal by appearing not to move but only to loom larger in the target's field of vision.
katydids have evolved a wide range of camouflage adaptations so their body colouring and shape match entire leaves, half-eaten leaves, dying leaves, leaves with bird droppings, sticks, twigs, and tree bark. Other well-known mimetic animals include beetles, mantids, caterpillars, moths, snakes, lizards, frogs, and fish.
A well known response of cephalopds when threatened is to release large volumes of ink. Some cephalopods also release pseudomorphs ("false bodies"); smaller clouds of ink with a greater mucus content, which allows them to hold their shape for longer. These are expelled slightly away from the cephalopod and are roughly the same volume and look similar to the cephalopod that released them. Many predators have been observed attacking them mistakenly, allowing the cephalopod to escape.
Counter-illumination camouflage is the production of light to blend in against a lit background. In water, light comes down from the surface, so when animals are seen from below, they appear darker than the background. Some species of cephalopod, such as the midwater squid and the sparkling enope squid, produce light in photophores on their undersides to match the background. Bioluminescence is common among marine animals, so counter-illumination camouflage may be a widespread mode of deception.
Colour change permits camouflage against different backgrounds. In the context of deception, this can be used as a defence or predatory strategy, or during courtship and mating. Colour change is made possible by chromatophores; pigment-containing and light-reflecting organelles in cells found in amphibians, fish, reptiles, crustaceans and cephalopods. Inside the chromatophore cell of cephalopods, pigment granules are enclosed in an elastic sac. To change colour, the animal distorts the sac by muscular contraction, changing its translucency, reflectivity or opacity. This differs from the mechanism used in fish, amphibians and reptiles, in that the shape of the sac is being changed rather than a translocation of pigment vesicles within the cell.
Some chameleon and anole species are able to voluntarily change their skin colours. Different chameleon species are able to change different colours which can include pink, blue, red, orange, green, black, brown, light blue, yellow, turquoise and purple. Some species, such as the Smith's dwarf chameleon, adjust their colours for camouflage in accordance with the vision of the specific predator species (bird or snake) that they are being threatened by.
Some octopuses can use muscles in the skin to change both the colour and texture of their mantle to achieve a greater camouflage. In some species, the mantle can take on the spiky appearance of seaweed, or the scraggly, bumpy texture of a rock, among other disguises. A few species, such as the mimic octopus, have another defence mechanism. They can combine their highly flexible bodies with their colour-changing ability to accurately mimic other, more dangerous animals, such as lionfish, sea snakes, and eels.
A well-researched form of deception is feigning death, often referred to by non-specialists as "playing dead" or "playing possum", although specialists use the terms "tonic immobility" or "thanatosis". A wide range of animals, e.g. lizards, birds, rodents, and sharks, will behave as if to appear dead, usually as a defensive method of avoiding predation as predators will usually take only live prey.
In beetles, artificial selection experiments have shown that there is heritable variation for length of death-feigning. Those selected for longer death-feigning durations are at a selective advantage to those at shorter durations when a predator is introduced. Death-feigning birds often take advantage of escape opportunities; tonic immobility in quail reduces the probability of the birds being predated by cats.
Death feigning can also be used in reproduction (e.g. in the nursery web spider, the male sometimes feigns death to avoid getting eaten by females during mating) and to improve predation (e.g. the predatory cichlid Haplochromis livingstoni will lie on its side on the bottom sediments until approached by scavengers attracted to what appears to be a dead fish, whereupon H. livingstoni abandons the pretence, rights itself and attacks the scavenger).
Death feigning behaviour can be deliberately induced by humans, particularly chickens, colloquially known as 'hypnosis'. According to Gilman et al. the investigation of ‘animal hypnosis’ dates back to the year 1646 in a report by Kircher. It has been shown that the intensity and duration of death feigning is related to the intensity of fear prior to the feigning state being induced. This has been used to show that hens in cages are more fearful than those in pens, hens on the top tier of battery cages are more fearful than those on the lower levels, hens carried by hand are more fearful than hens carried on a mechanical conveyor, and hens undergoing longer transportation times are more fearful than those undergoing transport of a shorter duration.
Concealment is the use of cover and terrain by the deceiver to hide from observation.
Some animals will select and carry around parts of the environment either to conceal themselves or behave as a form of mimicry based on the environment. In 2005, an article reported that the veined octopus has a bipedal behaviour. According to the article, this behaviour was discovered in octopuses in an area off Sulawesi, where the sandy bottom was littered with coconut shells. The bipedal motion appears to mimic a floating coconut. At least four individual veined octopuses have been observed retrieving discarded coconut shells, manipulating them, and then reassembling them to use as shelter. This discovery was documented in the journal Current Biology and has also been recorded on video. The octopuses carried the shells up to 20 m and has been described as the first discovered example of tool use in cephalopods.
Another form of concealment used by cephalopods is their tendency to release large amounts of dark ink when they are threatened. The ink obsucures the vision of the threatening animal and temporarily conceals the position of the cephalopod allowing it to escape.
Distraction displays, also known as deflection display, diversionary display or paratrepsis, are anti-predator behaviours used to attract the attention of a predator away from an object, typically the nest or young. They are particularly well known in birds but also occur in fish. The broken-wing display is well known in nesting waders and plovers and doves such as the mourning dove. Birds that are at the nest walk away from the nest with one wing hung low and dragging on the ground to appear as an easy target for a predator thereby deceiving predators and distracting their attention away from the nest or young.
The traditional view in ethology is that animal displays are almost always accurate barometers of the capabilities of the signaller, and that it is not possible for deception to become a stable feature of any such communication system. Deception in this case means that the signaller misrepresents its true capabilities in order to "win" a confrontation with a potential competitor. Ethologists argue that the widespread and continued use of deception by many individuals would cause the whole system to break down, as the recipients of the signal would become more "sceptical" about its validity as more and more deceivers’ bluffs are called.
However, deception seems to be a stable feature in communities of mantis shrimps, which spread their front limbs (known as "smashers") to threaten rivals. Newly moulted mantis shrimps frequently deceived potential competitors by spreading their front limbs, even though their still-soft exoskeletons meant that they could not use their smashers without damaging themselves, so the display was a bluff.
Some moths look threatening while at rest by displaying a sinister lurking face, such as those of genus Speiredonia, or the more aggressive face of a snake poised to attack, such as many species of genus Spirama. Adult Atlas moths of the genera Attacus and Rothschildia also display snake heads. The eyed hawkmoth displays its large eyespots on its wings and moves them slowly as if it were a vertebrate predator such as an owl.
Tactical deception (also referred to as functional deception) has been defined as "acts from the normal repertoire of [an] agent, deployed such that another individual is likely to misinterpret what acts signify, to the advantage of the agent" In other words, it is the active use of communicative or display skills already employed by the organism in order to mislead another individual. It has been specified in some studies that this is an intraspecific behaviour, meaning that it occurs between members of the same species. Most other kinds of deception are meant to fool members of a different species. Tactical deception can also be achieved when the deceiver withholds information by failing to perform an expected action, such as giving a warning call when danger is observed. This sort of deception can be costly to the user in that tactical deception mostly occurs in social animals which may lose trust of fellow group-members when their deceit is discovered.
The ability to employ tactical deception is thought to be either the product of a higher-functioning brain which allows the deceptive individual to project knowledge and beliefs on the target that are different from their own in order to manipulate the target using tools, vocalizations, gestures, or even other members of their family group; or a product of a brain evolved for rapid social learning allowing for quick manipulation of behaviour. The brain function attributed to the deceptive individual— whether the ability to predict another's mind or just clever use of learned behavioural cues in order to manipulate behaviour— is hotly debated and often changes with the species being observed. In the first scenario, the individual would be acknowledged as having the capacity for Theory of Mind (often seen abbreviated as ToM) which is the ability to attribute mental states (beliefs, knowledge, intents, desires, etc.) to another individual which are different and independent of one's own mental state. The second, often considered the more parsimonious explanation for the phenomenon of tactical deception, does not require a higher-functioning brain. It does, however, require specialized evolution of the parts of the brain which may responsible for social learning, such as the neocortex.
Brain Functionality: Brain tissue, which is more abundant in primates relative to body size than in any other mammal except for dolphins, is metabolically expensive. Therefore, there must be a large adaptive benefit for its overdevelopment in these species. The primary difference in brain size across the primates is due to size differences in the neocortex. Investigation into possible biological bases for neocortical development indicates that its evolution is likely very socially influenced and even selected-for in highly social species. In a study designed to use a measurable, direct indicator of social cognition— tactical deception by an individual to manipulate others in a social group— a strong correlation between the rate of social deception and size of the neocortex was discovered. This study involved 18 species (three strepsirrhines, four New World monkeys, seven Old World monkeys, and four ape species) for which neocortex size relative to total brain volume was compared.
Cephalopods: Some colour changes in cuttlefish may be tactical deception as they are able to simultaneously communicate two entirely different displays to two different observers. When a male cuttlefish courts a female in the presence of other males, he displays two different sides: a male pattern facing the female (courtship), and a female pattern facing away, to deceive other males.
Domestic pigs: Studies on pigs show that in trials where one trained animal reveals the source of food to another non-trained animal, these exploited food finders behave to increase the time they can spend at the food source before the scroungers arrive.
Birds: In an anecdotal account, Simmons reported that a female marsh harrier courted a male to obtain access to food he had stored. She then took this food and fed it to chicks which had been fathered by another male. More extensive studies focus on possibly deceitful behaviour in the pied flycatcher, a species in which males may possess more than one territory simultaneously. Females gain from mating with a male which has no other mates; males may attempt to deceive females about their mating status (mated or unmated). Females assess whether a male has already mated; if he is alone on a territory during repeated visits by the female, then he is probably unmated. Mated males will be absent from the territory (presumably because they are at another territory with their mate). By repeated sampling of male behaviour, females are usually able to avoid mating with previously mated males.
Group-foraging common ravens scatter hoard their food and also raid the caches made by others. Cachers withdraw from conspecifics when hiding their food and most often place their caches behind structures, obstructing the view of potential observers. Raiders watch inconspicuously and keep at a distance to cachers close to their cache sites. In response to the presence of potential raiders or because of their initial movements towards caches, the cachers frequently interrupt caching, change cache sites, or recover their food items. These behaviours suggest that ravens are capable of withholding information about their intentions, which may qualify as tactical deception.
great apes: Several great apes have been trained to use sign language and in some instances, have apparently used this to attempt to deceive human observers. Koko, a female gorilla, was trained to use a form of American Sign Language. It has been claimed that she once tore a steel sink out of its moorings and when her handlers confronted her, Koko signed "cat did it" and pointed at her innocent pet kitten.
Nim chimpsky was a chimpanzee also trained to use a form of American Sign Language. In a documentary about the chimp ("Project Nim") trainers claimed that when Nim got bored of learning to sign words she would sign 'dirty' indicating she wanted to go to the toilet, with the effect that the trainer stopped the lesson and took her to another room.
Observations on great apes have been widely reported as evidence of tactical deception. A well-known example involves a chimpanzee that was approached from behind by a loud aggressive rival. Here, the chimpanzee manipulated his lips several times before losing his fear grin and only after he had done so, he turned around to face the challenger, thereby concealing his fearful expression.
Studies on deceit in great apes have also been performed under experimental conditions, one of which is summarised by Kirkpatrick.
- "...food was hidden and only one individual, named Belle, in a group of chimpanzees was informed of the location. Belle was eager to lead the group to the food but when one chimpanzee, named rock, began to refuse to share the food, Belle changed her behaviour. She began to sit on the food until rock was far away, then she would uncover it quickly and eat it. rock figured this out though and began to push her out of the way and take the food from under her. Belle then sat farther and farther away waiting for rock to look away before she moved towards the food. In an attempt to speed the process up, rock looked away until Belle began to run for the food. On several occasions he would even walk away, acting disinterested, and then suddenly spin around and run towards Belle just as she uncovered the food."
Old world monkeys: In addition to the great apes, directly deceptive behavior has been observed in Baboons (Papio ursinus) which are part of the Old World monkeys. In one of their articles, Byrne and whiten recorded observations of what they refer to as "intimate tactical deception" within a group of baboons, and documented examples which they then broke into four separate "types" of deception. The four observed categories of deceptive behavior are as follows: A juvenile using warning screams to gain access to underground food storages which otherwise would have been inaccessible; an exaggerated "looking" gesture (which in an honest context would mean detection of a predator) produced by a juvenile to avoid attack by an adult male; recruitment of a "fall-guy" (a third party individual used by the deceiver to draw attention or aggression); and using one's own movement pattern to draw group-mates away from food caches. Byrne and whiten also broke these categories into subcategories denoting the modality of the action (e.g. vocalization) and what the action would have signified if observed in an honest context. They noted whether the individual that had been manipulated was in turn used to manipulate others, what the costs had been to the manipulated individual, and whether or not there were additional costs to third parties. Byrne and whiten expressed concerns that these observations might be rarities (more so than deception already would be in these individuals) and not actually be common behaviors in the species at all.
New world monkeys: Tufted capuchin (Cebus apella) monkey subordinates have been found to employ a vocal form of tactical deception when competing with dominant monkeys over valuable food resources. They will use alarm calls normally reserved for predator sightings— either barks (used specifically for aerial stimuli), peeps, or hiccups— to elicit a response in fellow group members and then take advantage of the distraction to pilfer food. In a series of experiments directed by Brandon Wheeler wherein a group of tufted capuchin monkeys was being observed and provided with platforms on which researchers had placed mounds of banana pieces, subordinates were responsible for nearly all of the alarm calls that could be classified as "false". In many of the false alarms, the caller was within two meters of the feeding platform. The event resulted in more dominant individuals reacting to the call by abandoning the platform. On four occasions, the caller then jumped to the platform immediately after the dominant had fled, and in three more cases, the caller made the alarm while on the platform and, when the other group-members were fleeing the platform, the subordinate caller stayed behind to eat.
Costs of tactical deception
Withholding information, a form of tactical deception, can result in costs of increased aggression by other group members. rhesus monkeys discovering food announce their discoveries by calling on 45% of occasions. Discoverers who fail to call, but are detected with food by other group members, receive significantly more aggression than vocal discoverers. Moreover, silent female discoverers eat significantly less food than vocal females. Because the cost of deception can be high for the deceivers if they are caught, tactical deception is a fairly rare occurrence. It is thought to be more common in forms and species where the cost of ignoring the possibly deceptive act is even higher than the cost of believing; for example, tufted capuchin monkeys employing alarm calls as deceptive tools. The cost of ignoring one of these calls could result in death, which may lead to a "better safe than sorry" philosophy even when the arbitrator is a known deceiver.
- Animal communication
- List of camouflage methods
- Military deception
- Origins of language
- Origin of speech
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