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Animal communication is any
behaviour on the part of one animal that has an effect on the current or
future behaviour of another animal. The study of animal communication,
called zoosemiotics (distinguishable from anthroposemiotics, the study
of human communication) has played an important part in the development
of ethology, sociobiology, and the study of animal cognition.
Intraspecies vs. interspecies communication
The sender and receiver of a communication may be of the same
species or of
different 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 suggests that we should modify the definition of communication in
some way, either by saying that communication should generally be to the
adaptive advantage of the communicator, or by saying that it involves something
more than the inevitable consequence of the animal going about its ordinary
life.
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 behavioral 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 poisonous bite. Sometimes, a behavioral change and
warning colouration will be combined, as in certain species of amphibians
which have a brightly coloured belly, but on which the rest of their body is
coloured to blend in with their surroundings. When confronted with a potential
threat, 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 shown by some
antelopes such as Thomson's gazelle in the presence of a predator; it has been argued that
this demonstrates to the predator that the particular prey individual is fit and
healthy 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, in effect deceiving them. A well-known example is the angler
fish, which has a fleshy growth protruding from its forehead and dangling in
front of its jaws; smaller fishes try to take the lure, and in so doing are
perfectly placed for the angler fish to eat them.
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 of interspecific 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.
Some people believe that it is possible for humans and animals to communicate
through
telepathy.
Intraspecies communication
The majority of animal communication, however, occurs within a single
species, and this is the context in which it has been most 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; often these occur in combination, so a
distinctive movement acts to reveal or emphasise a distinctive body part. An
example that was important in the history of ethology was the parent Herring
Gull's presentation of its bill to a chick in the nest. Like many gulls, the
Herring Gull has a brightly coloured bill, yellow with a red spot on the lower
mandible near the tip. When it returns to the nest with food, the parent 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. Investigations by Niko Tinbergen and his colleagues showed that the red colour of the bill,
and its high contrast, are crucial for eliciting the appropriate response from
the chick (It is unresolved whether this actually is an inborn behavior in all
its complexity, or simply a combination of generalized curiosity on part of the
chick, and generalized parental/feeding instincts acting together to produce a
simple learning process via reward. Gull chicks peck at everything that is
brightly colored, mainly red, yellow, white or shining, high-contrast objects,
but the parent's bill is the only such object that will constantly yield food as
a reward when pecked at. Accidental swallowing of pieces of brightly colored
plastic or glass is a common cause of mortality amongst gull chicks).
Another important forms of communication is
bird song, usually performed mainly by males, though in some species the sexes
sing in alternation (this is called duetting and serves mainly purposes of
strengthening pair-bonding and repelling competitors). Bird song is just the
best known case of vocal communication; other instances include the warning
cries of many monkeys, the territorial 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 these smells in places where they have been. Often the scented substance
is introduced into urine or feces. Sometimes it is distributed through sweat,
though this does not leave a semi-permanent mark as scents deposited on the
ground do. Some animals have glands on their bodies whose sole function appears
to be to deposit scent marks: for example Mongolian gerbils have a scent gland
on their stomachs, and a characteristic ventral rubbing action 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 they
reenter, 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 studied in particular detail. They
include:
agonistic interaction: everything to do with contests and aggression
between individuals. Many species have distinctive threat 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 the threatened individual will make if it is
acknowledging the social dominance of the threatener; this has the effect of terminating
the aggressive episode and allowing the dominant animal unrestricted access
to the resource in dispute. Some species also have affiliative
displays 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 the display of body parts, body postures (gazelles assume
characteristic poses as a signal to initiate mating), 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 make to each other: famous examples are the mutual
presentation of weed 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 and
manakins.
food-related signals: many animals make "food calls" that attract a
mate, or offspring, or members of a social group generally to a food source.
When parents are feeding offspring, the offspring often have begging
responses (particularly when there 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 von Frisch.
alarm calls: signals made in the presence of a threat from a predator,
allowing all members of a social group (and often members 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 face in
dogs, which
signals that a subsequent aggressive signal is part of a play fight rather
than 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. They include 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 its production. 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 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. It
was the fundamental insight of sociobiology that behaviours that benefited a
whole group of animals might emerge as a result of selection pressures 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 to emerge under individual selection. This led to the
realisation 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 signalling 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.
Communication and understanding
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. Richard 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.
Animal communication and human behaviour
Another controversial issue is the extent to which humans have behaviours
that 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 Iraneaus Eibl-Eibesfeldt have argued that facial gestures such as smiling,
grimacing, and the eye-brow flash on greeting are universal 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
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 the animals. For example, cats have a mild 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 probably work through their natural patterns of interspecific
communication.
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 meaningless phonetic elements, or phonemes. Animal signals, however, do not exhibit this dual structure.
Animal utterances are generally reflexes of external stimuli and thus
are not produced intentionally. They cannot refer to matters removed in time
and space (a possible exception is the information conveyed in
honeybee dance language).
Human language is learned, while animal communication systems are known
largely by
instinct.
Human languages combine elements to produce new messages (a property
known as creativity). This is not possible in animal communication
systems.
In contrast to human language, animal communication systems are not able
to express conceptual generalizations.