Animal communication is the transfer of information from one or a group of animals (sender or senders) to one or more other animals (receiver or receivers) which affects either the current or future behavior of the receivers. The transfer of information may be deliberate (e.g. a courtship display) or it may be unintentional (e.g. a prey animal detecting the scent of a predator). When animal communication involves multiple receivers, this may be referred to as an "audience". The study of animal communication is a rapidly growing area of study and plays an important part in the disciplines of animal behavior, sociobiology, neurobiology and animal cognition. Even in the 21st century, many prior understandings related to diverse fields such as personal symbolic name use, animal emotions, learning and animal sexual behavior, long thought to be well understood, have been revolutionized.
When the information sent from the sender to receiver is either an act or a structure that manipulates the behavior of the receiver, it is referred to as a "signal". Signalling theory predicts that for the signal to be maintained in the population, the receiver should also receive some benefit from the interaction. Both the production of the signal from the sender and the perception and subsequent response from the receiver need to coevolve. It is important to study both the sender and receiver of the interaction, since the maintenance and persistence of the signal is dependent on the ability to both produce and recognize the signal. In many taxa, signals involve multiple mechanisms, i.e. multimodal signaling.
- 1 Modes
- 2 Functions
- 3 Interpretation of animal behavior
- 4 Intraspecific
- 5 Interspecific
- 6 Other aspects
- 7 See also
- 8 References
- 9 External links
For information on the perception of visual signals, see Visual Perception
- Gestures: The best known form of communication involves the display of distinctive body parts, or distinctive bodily movements; often these occur in combination, so a movement acts to reveal or emphasize a body part. A notable example is the presentation of a parent herring gull’s bill to its chick signals feeding time. Like many gulls, the herring gull has a brightly coloured bill, yellow with a red spot on the lower mandible near the tip. When the parent returns to the nest with food, it stands over its chick and taps the bill on the ground in front of it; this elicits a begging response from a hungry chick (pecking at the red spot), which stimulates the parent to regurgitate food in front of it. The complete signal therefore involves a distinctive morphological feature (body part), the red-spotted bill, and a distinctive movement (tapping towards the ground)which makes the red spot highly visible to the chick. While all primates use some form of gesture, Frans de Waal came to the conclusion that apes and humans are unique in that only they are able to use intentional gestures to communicate. He tested the hypothesis of gesture evolving into language by studying the gestures of bonobos and chimps.
- Facial expression: Facial gestures play an important role in animal communication. It is a motor expression of one or multiple facial features in response to some event or a signal of intention for further actions. See emotion in animals for further information on possible signals of emotion. Dogs, for example, express anger through snarling and showing their teeth. In alarm their ears will perk up. When fearful, dogs will pull back their ears, expose their teeth slightly and squint their eyes. Jeffrey Mogil studied the facial expressions of mice during increments of increasing pain; there were five recognizable facial expressions; orbital tightening, nose and cheek bulge, and changes in ear and whisker carriage.
- Gaze following: Coordination among social animals is facilitated by monitoring of each other's head and eye orientation. Long recognized in human developmental studies as an important component of communication, there has recently begun to be much more attention on the abilities of animals to follow the gaze of those they interact with, whether members of their own species or humans. Studies have been conducted on apes, monkeys, dogs, birds, and tortoises, and have focused on two different tasks: "follow[ing] another’s gaze into distant space" and "follow[ing] another’s gaze geometrically around a visual barrier e.g. by repositioning themselves to follow a gaze cue when faced with a barrier blocking their view". The first ability has been found among a broad range of animals, while the second has been demonstrated only for apes, dogs (and wolves), and corvids (ravens), and attempts to demonstrate this "geometric gaze following" in marmoset and ibis gave negative results. Researchers do not yet have a clear picture of the cognitive basis of gaze following abilities, but developmental evidence indicates that "simple" gaze following and "geometric" gaze following are likely to rely on distinct cognitive foundations.
- Color change. Color change can be separated into morphological color change, in which changes occur in relation to stage of development, or physiological color change, in which color change is triggered by mood, social context, or abiotic factors such as temperature. Physiological color change is a versatile mode for communication across a diverse array of taxa. Some cephalopods, such as the octopus and the cuttlefish, have specialized skin cells (chromatophores) that can change the apparent colour, opacity, and reflectiveness of their skin. In addition to being used for camouflage, rapid changes in skin colour are used while hunting and in courtship rituals. The colour changes in cuttlefish can be especially intricate as they are able to communicate two entirely different signals simultaneously from opposite sides of their body. When a male cuttlefish courts a female in the presence of other males, he displays two different sides: a male pattern facing the female, and a female pattern facing away, to deceive other males. Many animals communicate information about themselves without necessarily changing their behaviour. For example, sexual dimorphism in size or pelage communicates which sex the animal is. Other passive signals can be cyclical in nature. For example, in olive baboons, the beginning of the female's ovulation is a signal to the males that she is ready to mate. During ovulation, the skin of the female's anogenital area swells and turns a bright red/pink.
- Bioluminescent communication. Communication by the production of light occurs commonly in vertebrates and invertebrates in the oceans, particularly at depths (e.g. angler fish). Two well known forms of land bioluminescence are fireflies and glow worms. Other insects, insect larvae, annelids, arachnids and even species of fungi possess bioluminescent abilities. Some bioluminescent animals produce the light themselves whereas others have a symbiotic relationship with bioluminescent bacteria. (See also: List of bioluminescent organisms)
Many animals communicate through vocalization. Vocal communication is essential for many tasks, including mating rituals, warning calls, conveying location of food sources, and social learning. In a number of species, males perform calls during mating rituals as a form of competition against other males and to signal females, including hammer-headed bats, red deer, humpback whales, elephant seals, and songbirds. For more information on bird song, see bird vocalization. In various species, whale vocalizations have been found to have different dialects based on region. Other instances of vocal communication include the alarm calls of the Campbell monkey, the territorial calls of gibbons, and the use of frequency in greater spear-nosed bats to distinguish between groups. Another example of an animal that gives alarm calls is the vervet monkey. The vervet monkey gives a distinct alarm call for each of its four different predators. The other monkeys will react in a specific way, depending on which alarm call is issued by an individual. For example, the alarm calls for pythons and eagles are different because the response to each predator must be different. If an alarm call is given for a python, the monkeys must climb into the trees to avoid the python. In contrast, if an alarm call is given for an eagle, the monkeys must get low to the ground and seek a hiding place. It is important for these alarm calls to be distinguishable, so that the monkeys can recognize the threat and respond appropriately. Prairie dogs also have very complex communication when it comes to predator detection. According to Con Slobodchikoff and others, prairie dog calls contain specific information as to what type of predator is present, how big it is and how fast it is approaching.
Not all animals use vocalization as a means of auditory communication. Many arthropods rub specialized body parts together to produce sound. This is known as stridulation. Crickets and grasshoppers are well known for this, but many others use stridulation as well, including crustaceans, spiders, scorpions, wasps, ants, beetles, butterflies, moths, millipedes, and centipedes. Another means of auditory communication is the vibration of swim bladders in bony fish. The structure of swim bladders and the attached sonic muscles varies greatly across bony fish families, resulting in a wide range of sound production. Striking body parts together can also produce auditory signals. A popular example of this is the tail tip vibration of rattlesnakes as a warning signal. Other examples include bill clacking in birds, wing clapping in manakin courtship displays, and chest beating in gorillas.
Despite being the oldest method of communication, chemical communication is one of the least understood forms due to the “noisy” nature and sheer abundance of chemicals in our environment, and the difficulty of detecting and measuring all chemical species within a sample. The primary function of chemical reception is to detect resources (i.e. food) and this function was an adaptive trait (adaptation) first derived in single-celled organisms (bacteria), living in the oceans, during the early days of life on Earth. Over evolutionary time, this function became more refined, allowing some organisms to differentiate between chemical compounds emanating from resources, conspecifics (same species; i.e., mates and kin), and heterospecifics (different species; i.e., competitors and predators). The ability to detect chemicals present within the environment allowed organisms to associate advantageous or adaptive behaviors with the information provided by the chemicals. For instance, a small minnow species may do well to avoid habitat with a detectable concentration of chemical cue associated with a predator species such as northern pike. Minnows with the ability to perceive the presence of predators before they are close enough to be seen and then respond with adaptive behavior (such as hiding) are more likely to survive and reproduce, as will their offspring due to the nature of inheritance (heredity).
A rare form of animal communication is electrocommunication. It is seen primarily in aquatic animals, though some land mammals, notably the platypus and echidnas are capable of electroreception and thus theoretically of electrocommunication.
Weakly electric fishes are an example of electrocommunication tied with an active sensory modality for electrolocation. These fish communicate by generating an electric field using what is known as an electric organ. This field, and any changes of it, is detected by electroreceptors. Differences in waveforms and frequencies convey information on species, sex, and individuals. Differences and changes in waveforms can be in response to hormones, circadian rhythms, and interactions with other fish. Some predators, such as sharks and rays, are able to eavesdrop on these electrogenic fish through passive electroreception.
Touch can be an important factor in social interactions, for example in fights or in a mating context. In both occasions, the use of touch will increase as an interaction escalates. In a fight, touch can be used to challenge an opponent, to coordinate movements during the escalation of the fight, and it can be used by the loser to perform submissive actions afterwards. Mammals will initiate mating by grooming, stroking or rubbing against each other. This provides the opportunity to assess chemical signals of the potential mate, or apply additional chemical signals. Touch is also used to announce the intention of the male to mount the female, such as a male kangaroo grabbing the tail of a female. During mating, touch stimuli are important for pair positioning, coordination and genital stimulation. In social integration, touch is a widely used communication system. The most widespread behaviour involving touch is allogrooming, the grooming of one animal by another. This has several functions; it removes parasites and debris from the body of the groomed animal, reaffirms the affiliative bond or hierarchical relationship between the animals involved, and gives the groomer an opportunity to examine olfactory cues on the groomed individual, perhaps adding additional ones. This behaviour has been observed in social insects, birds and mammals.
Another mechanism for social integration is prolonged physical contact or huddling. This can be used to transfer olfactory or tactile information, or for heat exchange. Some organisms live in constant contact in a colony, for example colonial corals. Because of the tight linkages between individuals, the entire colony can react on the aversive or alarm movements made by only a few individuals. In several herbivorous insect nymphs and larvae, aggregations where there is prolonged contact play a major role in group coordination. This may take the form of a procession or a rosette. The behaviour to form a rosette is called cycloalexy. Touch can also be a way to inform conspecifics about the environment. Some ant species recruit fellow workers to new food finds by first tapping them with their antennae and forelegs, then leading them to the food source while keeping physical contact. Another example of this is the waggle dance of honey bees.
Seismic communication is the exchange of information using self-generated vibrational signals transmitted via a substrate such as the soil, water, spider webs, plant stems, or a blade of grass among others. This communication holds many advantages such as being able to be sent regardless of light and noise levels, and having short ranges and short persistence with little danger of detection of predators. There are animals that use seismic communication from a large number of taxa. Some of these include, but are not limited to, frogs, kangaroo rats, mole rats, bees, and nematode worms. Tetrapods for the most part use a body part to drum against the ground to create seismic waves, which in turn are received through the sacculus. The sacculus is an organ in the inner ear containing a membranous sac that is used for balance aid, but in animals that use this communication can detect seismic waves. Vibrations and other communication channels are not necessarily mutually exclusive, but can be used in multi-modal communication.
Autocommunication is a type of communication system in which the sender and receiver are the same individual. The sender emits a signal that is altered by the environment and eventually is received by the same individual. Certain alterations code for specific conditions which provide information about the environment that can be used to indicate food, predators or conspecifics. Because the sender and receiver are the same animal, selection pressure maximizes signal efficacy, i.e. “the degree to which an emitted signal is correctly identified by a receiver despite propagation distortion and noise.” Autocommunication can be divided in two main systems. The first is active electrolocation found in the electric fish Gymnotiformes (knifefishes) and Mormyridae (elephantfish) and also in the platypus (Ornithorhynchus anatinus). The second form of autocommunication is echolocation, found in bats and Odontoceti.
Main article: Infrared sensing in snakes
The ability to sense infrared thermal radiation evolved independently in various families of snakes. Essentially, it allows these reptiles to “see” radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the prey at which it strikes. It was previously thought that the organs evolved primarily as prey detectors, but it is now believed that it may also be used in thermoregulatory decision making. The facial pit underwent parallel evolution in pitvipers and some boas and pythons, having evolved once in pitvipers and multiple times in boas and pythons. The electrophysiology of the structure is similar between the two lineages, but they differ in gross structural anatomy. Most superficially, pitvipers possess one large pit organ on either side of the head, between the eye and the nostril (Loreal pit), while boas and pythons have three or more comparatively smaller pits lining the upper and sometimes the lower lip, in or between the scales. Those of the pitvipers are the more advanced, having a suspended sensory membrane as opposed to a simple pit structure. Within the family Viperidae, the pit organ is seen only in the subfamily Crotalinae: the pitvipers. The organ is used extensively to detect and target endothermic prey such as rodents and birds, and it was previously assumed that the organ evolved specifically for that purpose. However, recent evidence shows that the pit organ may also be used for thermoregulation. According to Krochmal et al., pitvipers can use their pits for thermoregulatory decision making while true vipers (vipers who do not contain heat-sensing pits) cannot.
In spite of its detection of IR light, the pits’ IR detection mechanism is not similar to photoreceptors - while photoreceptors detect light via photochemical reactions, the protein in the pits of snakes is in fact a temperature sensitive ion channel. It senses infrared signals through a mechanism involving warming of the pit organ, rather than chemical reaction to light. This is consistent with the thin pit membrane, which allows incoming IR radiation to quickly and precisely warm a given ion channel and trigger a nerve impulse, as well as vascularize the pit membrane in order to rapidly cool the ion channel back to its original “resting” or “inactive” temperature.
There are many functions of animal communication. However, some have been studied in more detail than others. This includes:
- Communication during contests: Animal communication plays a vital role in determining the winner of contest over a resource. Many species have distinct signals that signal aggression or willingness to attack or signals to convey retreat during competitions over food, territories, or mates.
- Mating rituals: Animals produce signals to attract the attention of a possible mate or to solidify pair bonds. These signals frequently involve the display of body parts or postures. For example, a gazelle will assume characteristic poses to initiate mating. Mating signals can also include the use of olfactory signals or calls unique to a species. Animals that form lasting pair bonds often have symmetrical displays that they make to each other. Famous examples are the mutual presentation of reeds by great crested grebes studied by Julian Huxley, the triumph displays shown by many species of geese and penguins on their nest sites, and the spectacular courtship displays by birds of paradise.
- Ownership/territorial: Signals used to claim or defend a territory, food, or a mate.
- Food-related signals: Many animals make "food calls" to attract a mate, offspring, or other members of a social group to a food source. Perhaps the most elaborate food-related signal is the Waggle dance of honeybees studied by Karl von Frisch. One well known example of begging of offspring in a clutch or litter is altricial songbirds. Young ravens signal will signal to older ravens when they encounter new or untested food. Rhesus macaques will send food calls to inform other monkeys of a food source to avoid punishment. Pheromones are released by many social insects to lead the other members of the society to the food source. For example, ants leave a pheromone trail on the ground that can be followed by other ants to lead them to the food source.
- Alarm calls: Alarm calls communicate the threat of a predator. This allows all members of a social group (and sometimes other species) to respond accordingly. This may include running for cover, becoming immobile, or gathering into a group to reduce the risk of attack. Alarm signals are not always vocalizations. Crushed ants will release an alarm pheromone to attract more ants and send them into an attack state.
- Meta-communication: Signals that will modify the meaning of subsequent signals. One example is the 'play face' in dogs which signals that a subsequent aggressive signal is part of a play fight rather than a serious aggressive episode.
Interpretation of animal behavior
Animal behavior is sometimes very hard to interpret. It is not so hard to describe, but to give the right meaning to behavior is much harder. Psychological interpretations of animal behavior are often anthropomorphized, leading to wrong conclusions. On the other hand, the similarities between human behavior and certain animal behavior cannot be ignored. Anthropomorphizing behavior is most often applied to domesticated animals, like cats and dogs, and with apes, because of the close phylogenetic relationship to humans. An experiment on chimpanzees shows that a small “dose of anthropomorphizing” often gives better scientific results than when researchers try to describe all behavior objectively, but skepticism remains for this concept. Interpreting animal behavior is vital when considering the context in which the signal is produced. This context is important for the recipient, humans or otherwise, to get the intended meaning of a signal. Research about the right interpretation of animal behavior has been going on for decades. In 1955, Cherry said “meaning is... like the beauty of a complexion; it lies altogether in the eye of the beholder”. Although his research was mainly on human behavior, he also used it for animal behavior. The difficulty in studying the meaning of signals lies in the range of possible responses. The same gesture may have multiple meanings, depending on context and other associated behaviors. Because of this, generalizations such as "X means Y" are often, but not always, accurate. Combining the information from context and the signal itself, will provide a more thorough meaning of communication. For example, a domestic dog's simple tail wag may be used in subtly different ways to convey many meanings as illustrated in Charles Darwin's The Expression of the Emotions in Man and Animals published in 1872.
Combined with other body language, in a specific context, many gestures e.g. yawns, direction of vision, all convey meaning. Thus statements that a particular action "means" something, should always be interpreted as "often means". As with human beings, who may smile or hug or stand a particular way for multiple reasons, many animals also re-use gestures. The right interpretation of animal behavior can be critical, such as clinical research with laboratory animals. Certain behaviors indicates pain levels, which is important to perfect medical procedures, or ensure animal’s welfare and minimize pain. When animals are in pain, they often behave differently. When given pain relief, their behavior returns to normal.
Much animal communication occurs between members of the species and this is the context in which it has been most intensively studied. Most of the forms and functions of communication described above are relevant to intraspecific communication.
Many examples of communication take place between members of different species. Animals communicate to other animals with various signs: visual, sound, echolocation, vibrations, body language, and smell.
Prey to predator
If a prey animal moves, makes a noise or vibrations, or emits a smell in such a way that a predator can detect it, this is consistent with the definition of "communication" given above. This type of communication is known as interceptive eavesdropping, where a predator intercepts the message being conveyed to conspecifics.
There are however, some actions of prey species that are clearly communications to actual or potential predators. A good example is warning colouration: species such as wasps that are capable of harming potential predators are often brightly coloured, and this modifies the behaviour of the predator, who either instinctively or as the result of experience will avoid attacking such an animal. Some forms of mimicry fall in the same category: for example hoverflies are coloured in the same way as wasps, and although they are unable to sting, the strong avoidance of wasps by predators gives the hoverfly some protection. There are also behavioural changes that act in a similar way to warning colouration. For example, canines such as wolves and coyotes may adopt an aggressive posture, such as growling with their teeth bared, to indicate they will fight if necessary, and rattlesnakes use their well-known rattle to warn potential predators of their venomous bite. Sometimes, a behavioural change and warning colouration will be combined, as in certain species of amphibians which have most of their body coloured to blend with their surroundings, except for a brightly coloured belly. When confronted with a potential threat, they show their belly, indicating that they are poisonous in some way.
Another example of prey to predator communication is the pursuit-deterrent signal. Pursuit-deterrent signals occur when prey indicates to a predator that pursuit would be unproﬁtable because the signaler is prepared to escape. Pursuit-deterrent signals provide a beneﬁt to both the signaler and receiver; they prevent the sender from wasting time and energy ﬂeeing, and they prevent the receiver from investing in a costly pursuit that is unlikely to result in capture. Such signals can advertise prey’s ability to escape, and reﬂect phenotypic condition (quality advertisement), or can advertise that the prey has detected the predator (perception advertisement). Pursuit-deterrent signals have been reported for a wide variety of taxa, including ﬁsh (Godin and Davis, 1995), lizards (Cooper et al., 2004), ungulates (Caro, 1995), rabbits (Holley 1993), primates (Zuberbuhler et al. 1997), rodents (Shelley and Blumstein 2005, Clark, 2005), and birds (Alvarez, 1993, Murphy, 2006, 2007). A familiar example of quality advertisement pursuit-deterrent signal is stotting (sometimes called pronking), a pronounced combination of stiff-legged running while simultaneously jumping shown by some antelopes such as Thomson's gazelle in the presence of a predator. At least 11 hypotheses for stotting have been proposed. A leading theory today is that it alerts predators that the element of surprise has been lost. Predators like cheetahs rely on surprise attacks, proven by the fact that chases are rarely successful when antelope stot. Predators do not waste energy on a chase that will likely be unsuccessful (optimal foraging behaviour). Quality advertisement can be communicated by modes other than visual. The banner-tailed kangaroo rat produces several complex foot-drumming patterns in a number of different contexts, one of which is when it encounters a snake. The foot-drumming may alert nearby offspring but most likely conveys vibrations through the ground that the rat is too alert for a successful attack, thus preventing the snake's predatory pursuit.
Predator to prey
Typically, predators attempt to reduce communication to prey as this will generally reduce the effectiveness of their hunting. However, some forms of predator to prey communication occur in ways that change the behaviour of the prey and make their capture easier, i.e. deception by the predator. A well-known example is the angler fish, an ambush predator which waits for its prey to come to it. It has a fleshy bioluminescent growth protruding from its forehead which it dangles in front of its jaws. Smaller fish attempt to take the lure, placing themselves in a better position for the angler fish to catch them. Another example of deceptive communication is observed in the genus of jumping spiders (Myrmarachne). These spiders are commonly referred to as “antmimicking spiders” because of the way they wave their front legs in the air to simulate antennae.
Various ways in which humans interpret the behaviour of domestic animals, or give commands to them, are consistent with the definition of interspecies communication. Depending on the context, they might be considered to be predator to prey communication, or to reflect forms of commensalism. The recent experiments on animal language are perhaps the most sophisticated attempt yet to establish human/animal communication, though their relation to natural animal communication is uncertain. Lacking in the study of human-animal communication is a focus on expressive communication from animal to human specifically. Horses are taught not to communicate (for safety). Dogs and horses are generally not encouraged to communicate expressively, but are encouraged to develop receptive language (understanding). Since the late 1990s, one scientist, Sean Senechal, has been developing, studying, and using the learned visible, expressive language in dogs and horses. By teaching these animals a gestural (human made) American Sign Language-like language, the animals have been found to use the new signs on their own to get what they need.
The importance of communication is evident from the highly elaborate morphology, behaviour and physiology that some animals have evolved to facilitate this. These include some of the most striking structures in the animal kingdom, such as the peacock's tail, the antlers of a stag and the frill of the frill-necked lizard, but also include even the modest red spot on a European herring gull's bill. Highly elaborate behaviours have evolved for communication such as the dancing of cranes, the pattern changes of cuttlefish, and the gathering and arranging of materials by bowerbirds. Other evidence for the importance of communication in animals is the prioritisation of physiological features to this function, for example, birdsong appears to have brain structures entirely devoted to its production. All these adaptations require evolutionary explanation.
There are two aspects to the required explanation:
- identifying a route by which an animal that lacked the relevant feature or behaviour could acquire it;
- identifying the selective pressure that makes it adaptive for animals to develop structures that facilitate communication, emit communications, and respond to them.
Significant contributions to the first of these problems were made by Konrad Lorenz and other early ethologists. By comparing related species within groups, they showed that movements and body parts that in the primitive forms had no communicative function could be "captured" in a context where communication would be functional for one or both partners, and could evolve into a more elaborate, specialised form. For example, Desmond Morris showed in a study of grass finches that a beak-wiping response occurred in a range of species, serving a preening function, but that in some species this had been elaborated into a courtship signal.
The second problem has been more controversial. The early ethologists assumed that communication occurred for the good of the species as a whole, but this would require a process of group selection which is believed to be mathematically impossible in the evolution of sexually reproducing animals. Altruism towards an unrelated group is not widely accepted in the scientific community, but rather can be seen as reciprocal altruism, expecting the same behaviour from others, a benefit of living in a group. Sociobiologists argued that behaviours that benefited a whole group of animals might emerge as a result of selection pressures acting solely on the individual. A gene-centered view of evolution proposes that behaviours that enabled a gene to become wider established within a population would become positively selected for, even if their effect on individuals or the species as a whole was detrimental;
In the case of communication, an important discussion by John Krebs and Richard Dawkins established hypotheses for the evolution of such apparently altruistic or mutualistic communications as alarm calls and courtship signals to emerge under individual selection. This led to the realization that communication might not always be "honest" (indeed, there are some obvious examples where it is not, as in mimicry). The possibility of evolutionarily stable dishonest communication has been the subject of much controversy, with Amotz Zahavi in particular arguing that it cannot exist in the long term. Sociobiologists have also been concerned with the evolution of apparently excessive signaling structures such as the peacock's tail; it is widely thought that these can only emerge as a result of sexual selection, which can create a positive feedback process that leads to the rapid exaggeration of a characteristic that confers an advantage in a competitive mate-selection situation.
One theory to explain the evolution of traits like a peacock's tail is 'runaway selection'. This requires two traits—a trait that exists, like the bright tail, and a prexisting bias in the female to select for that trait. Females prefer the more elaborate tails, and thus those males are able to mate successfully. Exploiting the psychology of the female, a positive feedback loop is enacted and the tail becomes bigger and brighter. Eventually, the evolution will level off because the survival costs to the male do not allow for the trait to be elaborated any further. Two theories exist to explain runaway selection. The first is the good genes hypothesis. This theory states that an elaborate display is an honest signal of fitness and truly is a better mate. The second is the handicap hypothesis. This explains that the peacock's tail is a handicap, requiring energy to keep and makes it more visible to predators. Thus, the signal is costly to maintain, and remains an honest indicator of the signaler's condition. Another assumption is that the signal is more costly for low quality males to produce than for higher quality males to produce. This is simply because the higher quality males have more energy reserves available to allocate to costly signaling.
Ethologists and sociobiologists have characteristically analysed animal communication in terms of more or less automatic responses to stimuli, without raising the question of whether the animals concerned understand the meaning of the signals they emit and receive. That is a key question in animal cognition. There are some signalling systems that seem to demand a more advanced understanding. A much discussed example is the use of alarm calls by vervet monkeys. Robert Seyfarth and Dorothy Cheney showed that these animals emit different alarm calls in the presence of different predators (leopards, eagles, and snakes), and the monkeys that hear the calls respond appropriately - but that this ability develops over time, and also takes into account the experience of the individual emitting the call. Metacommunication, discussed above, also seems to require a more sophisticated cognitive process.
It has been reported  that bottlenose dolphins can recognize identity information from whistles even when otherwise stripped of the characteristics of the whistle; making dolphins the only animals other than humans that have been shown to transmit identity information independent of the caller’s voice or location. The paper concludes that:
The fact that signature whistle shape carries identity information independent from voice features presents the possibility to use these whistles as referential signals, either addressing individuals or referring to them, similar to the use of names in humans. Given the cognitive abilities of bottlenose dolphins, their vocal learning and copying skills, and their fission–fusion social structure, this possibility is an intriguing one that demands further investigation.—V. M. Janik, et al. 
Animal communication and human behaviour
Another controversial issue is the extent to which human behaviours resemble animal communication, or whether all such communication has disappeared as a result of our linguistic capacity. Some of our bodily features - eyebrows, beards and moustaches, deep adult male voices, perhaps female breasts - strongly resemble adaptations to producing signals. Ethologists such as Irenäus Eibl-Eibesfeldt have argued that facial gestures such as smiling, grimacing, and the eyebrow flash on greeting are universal human communicative signals that can be related to corresponding signals in other primates. Given how recently spoken language has emerged, it is very likely that human body language does include some more or less involuntary responses that have a similar origin to the communication we see in other animals.
Humans also often seek to mimic animals' communicative signals in order to interact with them. For example, cats have a mild affiliative response of slowly closing their eyes; humans often mimic this signal towards a pet cat to establish a tolerant relationship. Stroking, petting and rubbing pet animals are all actions that probably work through their natural patterns of interspecific communication.
Dogs have shown an ability to understand human communication. In object choice tasks, dogs utilize human communicative gestures such as pointing and direction of gaze in order to locate hidden food and toys. It has also been shown that dogs exhibit a left gaze bias when looking at human faces, indicating that they are capable of reading human emotions. It is interesting to note that dogs do not make use of direction of gaze or exhibit left gaze bias with other dogs.
A new approach in the 21st century in the field of animal communication uses applied behavioral analysis (ABA), specifically Functional Communication Training (FCT). This FCT previously has been used in schools and clinics with humans with special needs, such as children with autism, to help them develop language. Sean Senechal, at the AnimalSign Center has been using an approach similar to this FCT with domesticated animals, such as dogs (since 2004) and horses (since 2000) with encouraging results and benefits to the animals and people. Functional communication training for animals, Senechal calls "AnimalSign Language". This includes teaching communication through gestures (like simplified American sign language), Picture Exchange Communication System, tapping, and vocalisation. The process for animals includes simplified and modified techniques.
Animal communication and linguistics
For linguistics, the interest of animal communication systems lies in their similarities to and differences from human language:
- Human languages are characterized for having a double articulation (in the characterization of French linguist André Martinet). It means that complex linguistic expressions can be broken down in meaningful elements (such as morphemes and words), which in turn are composed of smallest phonetic elements that affect meaning, called phonemes. Animal signals, however, do not exhibit this dual structure.
- In general, animal utterances are responses to external stimuli, and do not refer to matters removed in time and space. Matters of relevance at a distance, such as distant food sources, tend to be indicated to other individuals by body language instead, for example wolf activity before a hunt, or the information conveyed in honeybee dance language.It is therefore unclear to what extent utterances are automatic responses and to what extent deliberate intent plays a part.
- In contrast to human language, animal communication systems are usually not able to express conceptual generalizations. (Cetaceans and some primates may be notable exceptions).
- Human languages combine elements to produce new messages (a property known as creativity). One factor in this is that much human language growth is based upon conceptual ideas and hypothetical structures, both being far greater capabilities in humans than animals. This appears far less common in animal communication systems, although current research into animal culture is still an ongoing process with many new discoveries.
A recent and interesting area of development is the discovery that the use of syntax in language, and the ability to produce "sentences", is not limited to humans either. The first good evidence of syntax in non-humans, reported in 2006, is from the greater spot-nosed monkey (Cercopithecus nictitans) of Nigeria. This is the first evidence that some animals can take discrete units of communication, and build them up into a sequence which then carries a different meaning from the individual "words":
- The greater spot-nosed monkeys have two main alarm sounds. A sound known onomatopoeiacally as the "pyow" warns against a lurking leopard, and a coughing sound that scientists call a "hack" is used when an eagle is flying nearby.
- "Observationally and experimentally we have demonstrated that this sequence [of up to three 'pyows' followed by up to four 'hacks'] serves to elicit group movement... the 'pyow-hack' sequence means something like 'let's go!' [a command telling others to move]... The implications are that primates at least may be able to ignore the usual relationship between an individual alarm call, and the meaning it might convey under certain circumstances... To our knowledge this is the first good evidence of a syntax-like natural communication system in a non-human species."
- Animal consciousness
- Anthrozoology (human–animal studies)
- Body language
- Dear enemy effect and Nasty neighbour effect
- Deception in animals
- Emotion in animals
- Forms of activity and interpersonal relations
- International Society for Biosemiotic Studies
- Origin of language
- Origin of speech
- Sir Philip Sidney game
- Talking animal
- Witzany, G., ed. (2014). Biocommunication of Animals. Dortrecht: SpringerISBN=978-94-007-7413-1.
- Maynard-Smith and Harper, 2003
- de Waal
- Langford, D.J. et al., (2010). Coding of facial expressions of pain in the laboratory mouse. Nature Methods, May 9th. pp. 1-3. doi:10.1038/nmeth.1455
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- Williams, Sarah (2012). "Two-faced fish tricks competitors". Science Now. Retrieved March 16, 2013.
- Motluk, Alison (2001). "Big Bottom". New Scientist 19 (7).
- Ehrlich, Paul R., David S. Dobkin, and Darryl Wheye. ""Bird Voices" and "Vocal Development" from Birds of Stanford essays". Retrieved 9 Sep 2008.
- Slabbekoorn, Hans, Smith, Thomas B. "Bird song, ecology and speciation." Philosophical Transactions: Biology Sciences 357.1420 (2002). 493-503.
- Carey, Bjorn. Whales Found to Speak in Dialects. Live Science. 3 Jan. 2006.
- Zuberbühler, Klause. "Predator-specific alarm calls in Campbell's monkeys, Cercopithecus campbelli." Behavioral Ecology and Sociobiology 50.5 (2001). 414-442
- Boughman, Janette W. "Vocal learning by greater spear-nosed bats." Proceedings: Biological Sciences 265.1392 (1998). 227-233
- Krulwich, Robert. "New Language Discovered: Prairiedogese". Retrieved 20 May 2015.
- Edwards, Lin (4 February 2010). "Prairie dogs may have the most complex language". Retrieved 20 May 2015.
- DeMello, Margo (2007). "Yips, barks and chirps: the language of prairie dogs". Retrieved 20 May 2015.
- "Prairie dogs' language decoded by scientists". CBC News. 21 June 2013. Retrieved 20 May 2015.
- Bradbury, J.W., and S.L. Vehrencamp. Principles of Animal Communication. Sunderland, MA: Sinauer Associates Inc., 2011. Print.
- Brown, G.E., D.P. Chivers, and R.J.F. Smith. 1995. Localized defecation by pike: A response to labelling by cyprinid alarm pheromone?. Behavioral Ecology and Sociobiology. 36.2: 105-110.
- "Electrocommunication". Davidson College. Retrieved 2011-03-03.
- Bradbury, J.W., and S.L. Vehrencamp. Principles of Animal Communication. Sunderland, MA: Sinauer Associates Inc., 2011.
- Narins, Peter M. "Seismic Communication in Anuran Amphibians." BioScience40.4 (1990): 268. Print.
- (Kardong & Mackessy 1991)
- (Krochmal et al. 2004)
- (Pough et al. 1992)
- (Gracheva et al. 2010)
- "Web of Life:Vibrational communication in animals". Retrieved 8 December 2012.
- Sean Senechal: Dogs can sign, too. A breakthrough method of teaching your dog to communicate to you, 2009, Random House/Crown/TenSpeed Press
- discussed at length by Richard Dawkins under the subject of his book The Selfish Gene
- V. M. Janik, L. S. Sayigh, and R. S. Wells: "Signature whistle shape conveys identity information to bottlenose dolphins", Proceedings of the National Academy of Sciences, vol. 103 no 21, May 23, 2006
- Hare, B., Call, J. & Tomasello, M.: "Communication of food location between human and dog (Canis familiaris).", Evolution of Communication, 2, 137–159, 1998.
- K. Guo, K. Meints, C. Hall, S. Hall & D. Mills: "Left gaze bias in humans, rhesus monkeys and rhesus domestic dogs." "Animal Cognition", vol. 12, 2009
- The Times May 18, 2006, p.3
- Brandon Kiem. "Rudiments of Language Discovered in Monkeys". Wiredscience. Retrieved 2013-03-15.
- Animal Communicator - Documentary
- The Elgin Center for Zoosemiotic Research
- Zoosemiotics: animal communication on the web
- The Animal Communication Project
- International Bioacoustics Council research on animal language.
- Animal Sounds different animal sounds to listen and download.
- The British Library Sound Archive contains over 150,000 recordings of animal sounds and natural atmospheres from all over the world.