| 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 as anthroposemiotics, the study of human communication) has played an important part in the development of
ethology, sociobiology, and
the study of animal cognition.
The Animal Communication
Project (http://acp.eugraph.com) includes an overview of the science of animal
communication (text from the book The Language of Animals) and 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 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.
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.
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,
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.
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). 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 faeces. 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, 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 the
mutual 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 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, 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 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 concern 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.
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