Animal communication

Animal communication is any behaviour on the part of oneanimal that has an effect on the current or future behaviour of another animal. The study of animal communication has played animportant part in the development of ethology , sociobiology , and the study of animalcognition .

The Animal Communication Project ] includes an overview of the science of animal communicationand regular updates about current scientifc research on animal communication.

Intraspecies vs. interspecies communication

The sender and receiver of a communication may be of the same species or ofdifferent species. The majority of animal communication is intraspecific (between two or more individuals of the same species).However, there are some important instances of interspecific communication. Also, the possibility of interspecific communication,and the form it takes, is an important test of some theoretical models of animal communication.

Interspecies communication

Prey to predator

If a prey animal moves or makes a noise in such a way that a predator can detect and capture it, that fits the definition of"communication" given above. Nonetheless, we do not feel comfortable talking about it as communication. Our discomfort suggeststhat we should modify the definition of communication in some way, either by saying that communication should generally be to theadaptive advantage of the communicator, or by saying that it involves something more than the inevitable consequence of theanimal going about its ordinary life.

There are however some actions of prey species that are clearly communications to actual or potential predators. A goodexample is warningcolouration : species such as wasps that are capable of harming potential predators areoften brightly coloured, and this modifies the behaviour of the predator, who either instinctively or as the result of experiencewill 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 areunable to sting, the strong avoidance of wasps by predators gives the hoverfly some protection. There are also behavioral changesthat 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, toindicate they will fight if necessary, and rattlesnakes use their well-knownrattle to warn potential predators of their poisonous bite. Sometimes, a behavioral change and warning colouration will becombined, as in certain species of amphibians which have a brightly colouredbelly, but on which the rest of their body is coloured to blend in with their surroundings. When confronted with a potentialthreat, they show their belly, indicating that they are poisonous in some way.

A more controversial example of prey to predator communication is stotting, a highly noticeable form of running shownby some antelopes such as Thomson's gazelle in thepresence of a predator; it has been argued that this demonstrates to the predator that the particular prey individual is fit andhealthy and therefore not worth pursuing.

Predator to prey

Some predators communicate to prey in ways that change their behaviour and make them easier to catch. A well known example isthe angler fish which dangles a lure in front of its jaws; smaller fishes tryto take the lure and are then easily captured.

Symbiotic species

Interspecies communication also occurs in various kinds of mutualism and symbiosis . For example, in the cleaner fish / grouper system, groupers signal their availability for cleaning by adopting a particular posture.

Human/animal communication

Various ways in which humans interpret the behaviour of domestic animals, or give commands to them, fit the definition ofinterspecific communication. Depending on the context, they might be considered to be predator to prey communication, or toreflect forms of commensalism. The recent experiments on animallanguage are perhaps the most sophisticated attempt yet to establish human/animal communication, though their relation tonatural animal communication is uncertain.

Intraspecies communication

The majority of animal communication, however, occurs within a single species, and this is the context in which it has beenmost intensively studied.

Forms of communication

Most of the following forms of communication can also be used for interspecific communication.

The best known forms of communication involve the display of distinctive body parts, or distinctive bodily movements; oftenthese occur in combination, so a distinctive movement acts to reveal or emphasise a distinctive body part. An example that wasimportant in the history of ethology was the parent Herring Gull 'spresentation of its bill to a chick in the nest. Like many gulls , the Herring Gull has abrightly coloured bill, yellow with a red spot on the lower mandible near the tip. When it returns to the nest with food, theparent stands over its chick and taps the bill on the ground in front of it; this elicits a begging response from a hungry chick,which stimulates the parent to regurgitate food in front of it. The complete signal therefore involves a distinctivemorphological feature (body part), the red-spotted bill, and a distinctive movement (tapping towards the ground) which makes thered spot highly visible to the chick. Investigations by Niko Tinbergen and his colleagues showed that the red colour of the bill, and its high contrast, are crucial for eliciting the appropriateresponse from the chick.

Another important forms of communication is bird song , usually performedmainly by males, though in some species the sexes sing in alternation (this is called duetting ). Bird song is just the best known caseof vocal communication; other instances include the warning cries of many monkeys , theterritorial calls of gibbons , and the mating calls of many species of frog .

Less obvious (except in a few cases) is olfactory communication. Many mammals,in particular, have glands that generate distinctive and long-lasting smells, and have corresponding behaviours that leave thesesmells in places where they have been. Often the scented substance is introduced into urine or faeces . Sometimes it is distributed through sweat, though thisdoes not leave a semi-permanent mark as scents deposited on the ground do. Some animals have glands on their bodies whose solefunction appears to be to deposit scent marks: for example Mongolian gerbils have a scent gland on their stomachs, and a characteristic ventral rubbingaction that deposits scent from it. Golden hamsters and cats have scent glands on their flanks, and deposit scent by rubbing their sides against objects;cats also have scent glands on their foreheads. Bees carry with them a pouch of material from the hive which they release as theyreenter, the smell of which indicates if they are a part of the hive and grants their safe entry.

Functions of communication

While there are as many kinds of communication as there are kinds of social behaviour, a number of functions have been studiedin particular detail. They include:

• agonistic interaction: everything to do with contests and aggression between individuals. Many species have distinctivethreat displays that are made during competition over food, mates or territory ; much bird song functions in this way. Often there is a matched submission display, which thethreatened individual will make if it is acknowledging the social dominance of the threatener; this has the effect of terminating the aggressive episodeand allowing the dominant animal unrestricted access to the resource in dispute. Some species also have affiliativedisplays which are made to indicate that a dominant animal accepts the presence of another
• courtship rituals: signals made by members of one sex to attract or maintain the attention of potential mate, or to cement a pair bond . These frequently involve thedisplay of body parts, or the emission of scents or calls, that are unique to the species , thus allowing the individuals to avoid mating with members of another species which would be infertile.Animals that form lasting pair bonds often have symmetrical displays that they pair make to each other: famous examples are themutual presentation of weed by Great-Crested Grebes , studied by Julian Huxley ,and the triumph displays shown by many species of geese and penguins on their nest sites.
• food-related signals: many animals make "food calls" that attract a mate, or offspring, or members of a social groupgenerally to a food source. When parents are feeding offspring, the offspring often have begging responses (particularly whenthere are many offspring in a clutch or litter - this is well known in altricial songbirds, for example). Perhaps the most elaborate food-related signal is the dance language of honeybees studied by Karl vonFrisch , though von Frisch's interpretation of this is currently controversial.
• alarm calls: signals made in the presence of a threat from a predator, allowing all members of a social group (and oftenmembers of other species) to run for cover, become immobile, or gather into a group to reduce the risk of attack.
• metacommunications: signals that modify the meaning of subsequent signals. The best known example is the play facein dogs , which signals that a subsequent aggressive signal is part of a play fight ratherthan a serious aggressive episode.

Evolution of communication

The importance of communication is clear from the fact that animals have evolved elaborate body parts to facilitate it. Theyinclude some of the most striking structures in the animal kingdom, such as the peacock 's tail. Birdsong appears to have not just peripheral but also brain structures entirely devoted to itsproduction. But even the red spot on a herring gull's bill, and the modest but characteristic bowing behaviour that displays it,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 thatmovements and body parts that in the primitive forms had no communicative function could be "captured" in a context wherecommunication would be functional for one or both partners, and could evolve into a more elaborate, specialised form. Forexample, Desmond Morris showed in a study of grass finches that a beak-wiping responseoccurred in a range of species, serving a preening function, but that in some species this had been elaborated into a courtshipsignal.

The second problem has been more controversial. The early ethologists assumed that communication occurred for the good of thespecies as a whole, but this would require a process of groupselection which is believed to be mathematically impossible in the evolution of sexually reproducing animals. It was the fundamental insight of sociobiology that behaviours that benefited a whole group of animals might emerge as a result of selectionpressures acting solely on the individual. In the case of communication, an important discussion by John R. Krebs and Richard Dawkins established hypotheses for the evolution of such apparently altruistic or mutualistic communications as alarm calls and courtship signals toemerge under individual selection. This led to the realisation that communication might not always be "honest" (indeed, there aresome obvious examples where it is not, as in mimicry). The possibility of evolutionarily stable dishonest communication has beenthe subject of much controversy, with Amotz Zahavi in particular arguingthat it cannot exist in the long term. Sociobiologists have also been concerned with the evolution of apparently excessivesignalling 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 anadvantage in a competitive mate-selection situation.

Communication and understanding

Ethologists and sociobiologists have characteristically analysed animal communication in terms of more or less automaticresponses to stimuli, without raising the question of whether the animals concern understand the meaning of the signals they emitand receive. That is a key question in animal cognition . There aresome signalling systems that seem to demand a more advanced understanding. A much discussed example is the use of alarm calls by vervet monkeys . Richard Seyfarth and Dorothy Cheney showed that theseanimals emit different alarm calls in the presence of different predators ( leopards , eagles , and snakes ), and the monkeys that hearthe calls respond appropriately - but that this ability develops over time, and also takes into account the experience of theindividual emitting the call. Metacommunication, discussed above, also seems to require a more sophisticated cognitiveprocess.

Animal communication and human behaviour

Another controversial issue is the extent to which humans have behaviours that resemble animal communication, or whether allsuch communication has disappeared as a result of our linguistic capacity. Some of our bodily features - eyebrows, beards andmoustaches, deep adult male voices, perhaps female breasts - strongly resemble adaptations to producing signals. Ethologists suchas IraneausEibl-Eibesfeldt have argued that facial gestures such as smiling, grimacing, and the eye-brow flash on greeting areuniversal human communicative signals that can be related to corresponding signals in other primates . Given the recency with which spoken language has emerged, it is likely that human body language does include some more or less involuntary responses that have asimilar origin to the communication we see in other animals.

Humans also often seek to mimic animals' communicative signals in order to interact with the animals. For example, cats have amild affiliative response involving closing their eyes; humans often close their eyes towards a pet cat to establish a tolerant relationship. Stroking, petting and rubbing pet animals are all actions that probablywork through their natural patterns of interspecific communication.