AMER ZOOL.. 17:155-165(1977).
What Is a Display?
C. G. BEER
Institute of Animal Behavior, Rutgers University, Newark, New Jersey 07102
Scientists, by and large, place little value
on elegance or refinement in the use of
words, but they do insist, as a rule, on
rigorous and clear definitions in the language of their trade. The terms in which
the definitions should be couched have
been a matter of debate: Lord Kelvin maintained that statements should not be regarded as scientific unless they could be
expressed in numbers; Ernst Mach argued
that the terms of a science must ultimately
refer to sensations; P. W. Bridgeman held
that scientific terms mean the "operations"
involved in their application; and there
have been those, like Einstein, who have
opposed such reductionist views with what
could be called constructivist approaches
to the uses of concepts in science. But
whatever the position taken about the
meaning of "meaning," science is seen as
overcoming the vagaries of ordinary discourse by pinning meanings down with
sharp definitions.
At least such is supposed to be the case
in the so-called hard sciences of physics
and chemistry. Biology may be another
matter; and although psychology has been
recurrently preoccupied about problems
of definition, it appears to have had only
passing success in solving them. Ethology,
however, sometimes gives the impression
of being averse to definition, and even of
making an ally of ambiguity. Its dealings in
"instinct," for example, have let vagueness
and multiple meaning carry argument
over what might otherwise be regarded
as barriers to inference, but with pernicious consequences for the integrity of
thought.
Now while too little concern with matters of definition can give thought the
freedom to lose itself in the flyways of
fallacy, too much concern with definition
can have the opposite effect of restricting
thought to beaten paths within which it has
little freedom at all. If a concept can be
said to have life in the sense that it can
grow and accommodate to the assimilation
of new knowledge, then it can also be said
that by purporting to fix meaning once
and for all strict definition is a threat to
that life—rigour of definition risks rigor
mortis of concept. Of course one can also
say that scientific concepts eventually mature, along with the theories within which
they have their place, to the point where
further growth is no longer to be expected,
the meaning having settled into its final
form for the theory to do all the work
assigned to it. The definitions that the
Newtonian system brought to such concepts as force and work exemplify this
coming of age in science. But, as Kaplan
(1964) and others have pointed out, there
are numerous cases of concepts evolving
with the evolution of their science, which
argue that closure of meaning should not
be forced, but allowed to arrive in its own
due time. A certain degree of "open texture" (Waismann, 1953) in the meanings
of terms is therefore to be tolerated in a
science, in the interest of avoiding premaResearch reported in this paper was supported by ture aging. Terms such as "gene" and
Grant #MH 16727 from the U.S. Public Health "mutation" in genetics, "hormone" and
Service, and carried out in the Brigantine National
"synapse" in physiology, "niche" and
Wildlife Refuge, New Jersey, with the permission and
"competition"
in ecology exemplify ways in
cooperation of the U.S. Fish and Wildlife Service.
which meaning moves with the maturation
The help and hospitality of the Refuge Manager and
his staff are gratefully acknowledged. I also thank Dr. of a science. "Display" may do the same in
W. John Smith for permission to quote from his book, ethology.
which is in press.
155
156
C. G. BEER
However such change of meaning as
might occur to a scientific term can differ
according to whether one attends to what
the term classes together or what the qualifications for class membership are. The
distinction has been variously marked as
between denotation and connotation, extension and intention, reference and
sense, ostensive and verbal definition. To
adapt an example from Wittgenstein
(1958:2), you can indicate what is meant by
"pencil" by pointing to a pencil, but in so
doing you leave open the question of
which properties of the object entitle it to
be so called: its shape, its being made of
wood and graphite, its usefulness for writing and drawing, and so on. The ostensive
basis of a concept may change little if at all
as progress in its science transforms what
the concept means within the context of
prevailing theory; but change in the connotation can also result in widening or
narrowing of the denotation.
The concept of homology provides a
good example of the sort of thing I have in
mind. Prior to the ascendancy of Darwinian evolution in biology, homology meant
correspondence between parts of different
structures sharing the same basic structural design, with no implications about
origins (Russell, 1961). The Darwinian
theory initially provided explanation for
the existence of such correspondences, but
this explanation has come to pre-empt the
original meaning of the term, so that one
now finds homology defined in terms of
descent from common origin, in most
biology texts (e.g., the glossary definition in
Wilson, 1975:586). Nevertheless the ostensive bases for the concept remain where
they always were: in the comparison of
formal relationships in anatomical structures. At least this is the case for structural
homologies. Behavioural homologies are
another matter, even more tangled, about
which I shall have more to say later. It
affects what we may mean when we label
some kind of action as a display.
The kinds of action that we label displays are easy to exemplify from the behaviour of amphibia and reptiles, perhaps
the most familiar being the headbobbing
movements and dewlap extensions of
males in many species of lizards. However
birds take pride of place as performers of
display behaviour, for they do it, many of
them, where it can be easily observed, and
in such a variety of forms, many so spectacular as to seem opposed to utility, that
they have been favourite subjects of study
for ethologists from the beginning. Birds
drew attention to displays and displays
drew attention to birds. For this reason,
and because my own work has been devoted mainly to birds, I shall draw on bird
studies for most of my examples in what
follows. In any case birds can be considered as "feathered reptiles," and only the
tradition of the classification makes them
appear to have less in common with crocodiles than do snakes or turtles.
For ostensive definition of "display,"
then, one can hardly do better than point
to such remarkable exhibitions as the
peacock's tail spread, the Argus pheasant's
wing spread, and the posturing of Birds of
Paradise. These examples are displays
even in the common parlance sense of the
word, being visually conspicuous presentations of colour, form and movement in
what one has little hesitation in describing
as "showing off." The features of form and
colour pattern so presented appear to exist
for no other reason than to be "shown off"
in the ways they are. But "showing off," or
display in this sense, can hardly be regarded as an end in itself, at least by a
biologist.
In the more technical usage to which the
term is put in ethology, "display" has acquired functional and evolutionary connotations; and these have reflected back on
its denotion. In addition to the conspicuously visible showings-off of the sorts just
mentioned, displays, for the ethologist, include all sorts of less ostentatious ways in
which animals draw attention to themselves, or some feature of their situation,
by movement or posture, and also by
sound and even smell, taste, touch, and
electricity. What all of these productions
have in common is that they appear to
serve a signal or communication function,
and to have been evolutionarily "designed"
to that end.
How do we know that a certain way of
WHAT IS A DISPLAY?
behaving has a signal or communication
function? The answer that one is most
likely to receive is that in the case of such
behaviour its performance by one animal
can be observed to influence the behaviour
of another in some regular and predictable
manner. This, for example, is what J. M.
Cullen (1972: 102) says he means by
"communication"; and E. A. Armstrong
(1942:12) similarly construed "display" in
157
framework within which display behaviour
had been set—from which, indeed, the
notion of display had acquired much of its
meaning. According to this view, which
was that of what is now often referred to as
"Classical Ethology," displays function as
social releasers: that is to say, they provide
the sign stimuli that engage specific innate
releasing mechanisms in the recipient individuals and so elicit the social responses
his book Bird display and behaviour: "Un- controlled by these mechanisms (c.f., Tinder the term 'Display' I include move- bergen, 1951, 1953). Some variability in
ments, postures and sounds, generally of a kind and degree of response was allowed
conventionalised kind, which have the for, as resulting from difference in the
capacity to initiate specific responses in level to which an innate releasing
other creatures, more particularly in mechanisms might be loaded with motivamembers of the same species."
tional excitation from within, and in the
Much of what is regarded as display completeness or intensity of the sign
behaviour, however, is recognized as such stimuli from without (c.f., Lorenz's
before there is any clear understanding of "method of dual quantification"; e.g.,
its communication function. In some cases Lorenz, 1950). However, the variability
the behaviour just looks or sounds as actually observed in sequences of social
though it must be for communication, interaction turned out to be in excess, both
being showy or shrill, heraldic or his- qualitatively and quantitatively, of what
trionic, in ways that appear to serve no seemed plausibly consistent with the classiother purpose. When a peacock spreads cal conception.
and quivers his tail it is usually in the
As Lorenz (1952) gloomily forecast that
presence of a peahen, and the peacock it would, ethology turned to what he depositions himself face on the peahen, and scribed as "completely intangible statistical,
moves with her movements, so as to keep perhaps even cybernetic methods" (transthe full view of his array directly before lation in Schiller, 1957: 310) to deal with
her. Similarly a cock Amherst pheasant the true complexity in the ordering of
places himself side on to a female, and animal behaviour, including social comspreads only on the side toward her, when munication. The stark pictures of linear
he adopts the posture in which he com- sequences, such as the saw-tooth pattern
bines fanning of the neck-cape with unila- that Tinbergen drew for the courtship of
teral wing and leg extension. In such cases Three-spined Sticklebacks (Ter Pelkwikj
the behaviour is clearly directed towards and Tinbergen, 1937; Tinbergen, 1951),
another individual, but its reception may gave way to opulant pictures in which
vary from indifference to apparent an- arrows arched between nearly all permutanoyance and only occasionally may be tions of transition pairs in the set of besomething at all obviously in the cock's haviour patterns making up the class of
interest. In other cases, such as much of interaction sequences in question, the
the singing of male songbirds, the be- thickness of an arrow telling the frequency
haviour is performed, much of the time, in or probability of the transition it repthe absence of other individuals towards resented (e.g., the diagrams of courtship
which it is at all definitely directed and sequences of guppies given by Baerends^
upon which it can be seen to have regular al., 1956). These pictures, in their turn,
and consistent effects.
faded from fashion as their places were
taken
by tables of partial correlation
When ethologists began really to recogcoefficients
and transition matrices from
nize the extent of variability in response to
which
factor
analyses and Markov chains
displays, in many cases, they had to queswere
drawn
(e.g.,
Wiepkema, 1961; Neltion the adequacy of the theoretical
158
C. G. BEER
son, 1964; Hazlett and Bossert, 1965;
Altmann, 1965). For those who believe,
with Lord Kelvin, that all science aspires to
the condition of mathematics, these developments in the study of animal communication must have made it look as
though ethology were headed in the right
direction.
However, these quantitative methods of
analysis have methodological problems,
for many of which they do not provide the
means of solution. In the first place they
assume a prior qualitative analysis of the
behaviour into categories of acts, displays,
responses, or whatever, between which the
transitions are to be scored, the contiguities timed, the correlations computed,
and so forth. Statistical tests could not have
decided the issues between "molecular"
and "molar" behaviourism; no more can
they determine whether behaviour should
be described in terms of "movements" or
in terms of "actions" (c.f., Taylor, 1964),
i.e., as motor patterns such as flexion and
extension, running and coiling, or as patterns picked out on the basis of their
means-end relationships, such as fleeing
and attacking, hunting and building. Even
where there is agreement about what general kind of description is appropriate,
there may be disagreement between
"lumpers" and "splitters" about what
should be counted as a unit of behavior for
quantitative purposes. Where some tally
fights, songs and journeys, others tally
blows, notes and footsteps. Choice of time
unit may also precede analysis, and profoundly influence what the analysis produces (e.g. Hinde, 1970: 197-8). For
example the number of "courtship feedings" and the number of copulations are
highly positively correlated in half-hour
samples of the pre-laying behaviour of
mated Laughing Gulls, but on the basis of
occurrence within one minute of each
other, these two activities do not appear to
be associated (personal observation). The
crowing of one rooster has a short-term (of
the order of seconds) inhibitory effect on
the crowing of another, but a stimulating
effect over a longer (of the order of minutes) time range (Schleidt, 1973); and similar relationships have been found in the
calling of crickets (Busnel and Loher, 1961;
Heilegenberg, 1966, 1969). In cases such
as these the conclusions will be relative to
the time ranges chosen, or the way in
which the behaviour has been partitioned
or packaged temporally by the investigator.* Stochastic analyses that assume
the Markovian model in behaviour sequences deal solely with order, and so usually disregard the possibility that there
might be significance in variations of duration or interval. The only way in which the
Markov chain approach can take account of
such variation [by scoring the transitions
between short time intervals of equal duration (Parzen, 1962)] involves such large
volumes of data that it is more a theoretical
than a practical option.
Another problem in statistical analysis of
behavioural sequences is that its deliverances may differ from case to case, from
time to time, or from place to place. Such
lack of consistency, or "stationarity" as it is
technically called, would seem to be contrary to the requirements for effective
communication, at least according to what
has generally been assumed to be typical of
animal communication. Its appearance in
an analysis of communication could mean
that wrong assumptions had been made,
such as disregard of the possibility that
individual recognition might affect response to a signal, or that we have a case of
misplaced precision—of fine dissection directed at aspects of the behaviour that are
not centrally relevant to how it works as
communication. These and yet other
difficulties in the statistical analyses of behaviour sequences have been recently discussed by Slater (1973) and Simpson
(1973). The situation is such that it can
hardly be said that the quantitative approaches have provided unequivocal
* However, choice of boundary lines is sometimes
based on statistical analysis of the temporal features
of behaviour sequences. For example, Marler and
Isaac (1960) found a marked discontinuity in histograms of intervals between notes in vocalizations of
Chipping Sparrows, which they used to mark off
songs in this species; and plotting durations or intervals as log-survivorship curves has been used in
deciding what to regard as a bout of behaviour (e.g..
Nelson, 1964; Slater, 1975).
WHAT IS A DISPLAY?
means of discovering the communication
functions of display behaviour, and hence,
if communication function is a defining
characteristic of displays, of determining
what is and what is not to be regarded as a
display.
Part of the problem we have here is that,
more often than not, statistics is a means of
testing hypotheses rather then a means of
discovery. The ways in which statistical
techniques are put to work in studies of
communication will depend upon the conception of communication that is thought
to apply to whatever case is in question;
and the conception may differ from case to
case and be changed from time to time as
new facts come to light or new possibilities
come to mind. For example, Schleidt's
(1973) idea of "tonic communication," according to which rate of repetition of a
"key sign" may be a quantity in which
information is coded, will direct an investigator to look for correlation between
variation in signal rate and variation in
whatever it might appear that the signaller
is signalling about, in situations in which
someone working to the Markov model of
communication would attend to time only
in the sense of "before and after."
Another conception of communication
is incorporated in the "message-meaning
analysis" of W. J. Smith (e.g., 1968). This
conception brings in the notion of context
to account for the variability in sequences
of social interactions that frustrates the
defining of displays in functional terms.
Smith harks back beyond the Shannon and
Weaver era in the study of communication
to the less mathematical but equally
operationistic doctrines of the semiotics of
Charles Morris (1938). Morris divided the
discipline of semiotics — the theory of
signs—into three parts: semantics, which
has to do with the encoding of information
in signs; syntactics, which concerns the
physical characteristics of signs and the
channels via which they are transmitted;
and pragmatics, the study of the decoding
of information from signs, which operationally amounts to observation of the
changes that reception of a sign effects in
the behaviour of a recipient (c.f., Marler,
1961). According to Smith, a particular
159
sign may be semantically invariant but
pragmatically variable, because the state,
sex, social status or some other condition
of the recipient, or differences in the circumstances in which the sign is transmitted
and received, affect how the sign is responded to. These factors contributing to
what a sign can cause a receiver to do,
Smith refers to as the "context" of sign
transmission. What the sign signifies about
the signaller he calls the "message" of the
sign, and what the sign effects in the behaviour of the receiver he calls the "meaning" of the sign. The relationship of messages to meanings can be one-many, because context can add variety to what is
signified by signs.
Initially Smith's concept of the message
appeared to be that the message informed
about the motivational, or physiological, or
central-nervous state of the signaller (e.g.,
Smith, 1968:46). More recently he has
changed or clarified his position to the
effect that messages tell about the signaller's behavioural tendencies, and hence
what it is likely to do next (Smith, 1977).
For example, observations of what a
territory-holding bird does immediately
after performing a putative threat display
may indicate that the display is a sign of
hesitancy between moving or remaining
stationary. This indecisiveness between alternatives, according to Smith, is the message of the display, not whatever motivational factors cause it. For one thing we
cannot perceive the central-nervous state,
or whatever else might be supposed to be
giving rise to the display, at least not as
directly as we can perceive the hesitancy.
For another thing, if the display is used in
a variety of situations between which there
may be good reason to believe that the
motivational states of the displayers must
differ, as, for example, between fighting
and courtship, the association between the
display and hesitancy to move may be the
only feature common to all the situations.
Smith (1966, 1968) has analyzed the "kitter" call of the Eastern Kingbird (Tyrannus
tyrannies) along these lines. The call, between perches, is used during flight by "advertising" males; by both males and females
when approaching one another during
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C. G. BEER
courtship; when showing signs of taking
flight in the direction of a predator or, in
flight, when changing direction towards or
away from the predator; during incubation, by females when about to fly from the
nest in the absence of the male; by newlyfledged young when flying after their parents for food, at the stage when their
begging has begun sometimes to be repulsed by attack from the parents. The
behavioural correlations running through
all of the situations in which the kingbirds
give the "kit-ter" call led Smith to the
conclusion that the call provides the information that the caller is vacillating between
flying or staying put, or between flying
towards or flying away from something, or
between flying and landing. Accordingly
he labelled the call as a "Locomotory Hesitance Vocalization" (Smith, 1968: 52).
In thus working out the messages encoded in displays Smith (1977) has drawn
up a list of "general messages," consisting
of the kinds of messages having widespread distribution in the display repertoires of species in which social communication has been studied. The length of this
list of general messages is quite short, since
the information conveyed by each of the
kinds of message included is so broad in
scope and thin in detail that the list covers
a wide diversity of displays and leaves little
that cannot be brought within its range.
There is at least a suggestion of convergence between Smith's list of general
message and Moynihan's (1970) conclusion that the numbers of "major" displays
in the repertoires of different species are
lower and more uniform than might have
been expected. Indeed it would not be
surprising if someone were to try pressing
the notion of general message into service
in the effort to deal with the issue of
behavioural homology.
However, Smith also recognizes that
there are messages specific to certain displays of certain species, and that messages
telling about behaviour may be accompanied by or incorporate messages giving
species or individual identification, information about sex, age, rank, and so forth.
Even so he is convinced that information
about the signaller's behaviour is the main
message of a display. Furthermore he believes that for each kind of display there is
but one kind of behavioural message, or, at
most, a limited set of messages all about
the same kind of behavioural tendency. In
contrast to the one-many relationships of
displays to function or meanings, the relationship of displays to messages is supposed to be essentially one-to-one.
Message, in the sense of information
made available about a performer's behavioural tendencies, thus presents itself
as an alternative to function, in the sense
of effect on the behaviour of other individuals, as a criterion for deciding the
question "What is a display?" According to
Smith (1977): "A display is an act that can
be performed by an individual and is
specialized in form or pattern of employment to make a consistent set of kinds of
messages available to at least one other
individual." And: ". . . display units . . . are
the smallest (briefest) acts that provide
consistent information about non-display
behavior" (ibid.). However, by thus being
made a matter of definition, the relationship of displays to messages becomes a
premise for inference instead of a matter
that could be a conclusion from observation. For the units or categories of communication that have been in use, in
analyses of social behaviour of animals, the
rules relating these units or categories to
what they communicate — indeed the
question of what they communicate—still
remain open to investigation, at least in the
majority of cases. The definition of display
and display units in terms of message still
leaves us with the hiatus between ostensive
and connotative criteria: There are patterns of behaviour that we perceive as
displays on the basis of characteristics of
form and context but about which we have
no clear ideas as far as their messages are
concerned. Moreover there is at least the
possibility that some animals may have
ways of using one kind of communication
behaviour for communicating more than
one kind of message. The Laughing Gull's
use of its "long-call" offers a case in point.
The Long-call of the Laughing Gull
gives the bird its name. It consists of a
string of notes, beginning with a group of
WHAT Is A DISPLAY?
relatively short rapidly repeated notes, followed by a group of longer, less quickly
repeated notes, and usually ending with
one or more "head-toss notes," the whole
sequence sounding a bit like mocking
laughter. However, to a person who knows
bird calls this call is unmistakably that of a
gull, for though in its particular features it
is peculiar to the Laughing Gull, its general character is held in common with what
are also called long-calls in the repertoires
of other species of gulls. As we experience
it, the Laughing Gull's long-call, together
with the postures in which it is performed,
is a distinct, regularly recurring pattern of
communication behaviour, which could
well serve as a paradigm of what an
ethologist means when he talks of display.
Yet neither the messages encoded in the
display, nor the meanings derived from it,
have so far been worked out to anywhere
near a full understanding. It is known that
the call is individually characteristic in
some of its features, which serve for individual recognition (Beer, 1970, 1973).
Consequently reactions to a gull's long-call
differ according to the relationship of the
hearer to the caller. Further pragmatic
diversity is associated with the wide range
of situations, and hence contexts, in which
the call is used, so that an individual will
react differently on different occasions to
the long-call of the same gull. But even in
the same situation it sometimes happens
that one individual shows variable reaction
to the long-call of another.
For example, a chick responds to some
of the long-calls of its parents by calling in
reply and approaching, but to others it
appears not to show any response at all.
Observation suggested that the reason for
this difference was simply that the calls to
which the chicks respond are those that a
parent directs towards them, the calls they
ignore being oriented elsewhere, usually
towards adult gulls—the mate, neighbours
or foreigners. However chicks sometimes
appear to be able to make the discrimination between these two classes of longcall—those directed towards them and
those not—even when the parent is hidden from them and they cannot see the
direction in which it is oriented. This was
161
proved to be the case by a playback experiment in which chicks were tested indoors
with recordings of calls that had been
directed towards them and calls that had
been directed at adults. The chicks showed
significantly greater positive response to
the calls that had been directed at them
than to the calls that had not, yet the latter
were apparently recognized as coming
from one of the parents, for they did not
elicit any of the negative response shown
to such recordings of long-calls of adults
other than the parents (Beer, 1973, 1975).
Comparison of sonagrams of the recordings used in this experiment, and of other
recordings of long-calls categorized as
chick-directed or adult-directed, revealed
differences in the amplitude modulation in
the short-note sections: In the chickdirected calls the first one or two shortnotes were louder than those following; in
the adult-directed calls the first one or two
short-notes were softer than the rest, or
the notes got progressively louder as they
succeeded one another (Beer, 1975).
When listened for in the field, this difference, which had not been noticed before,
turned out to be quite easy to hear.
We can thus conclude that, at least as far
as using the long-call to communicate with
its chicks is concerned, a Laughing Gull
has the option of varying features of the
call to vary its meaning, and, evidently, its
message as well—for what a chick-directed
call tells about a parent's behavioural inclinations appears to have little, if anything,
in common with what an adult-directed
call might tell. There are also other variable features of the long-call that correlate
with differences in context, suggesting that
the use of syntactic flexibility to give
semantic and hence pragmatic versatility
to the Laughing Gull long-call is not restricted to specifying the address of calls
uttered by a parent in the presence of its
chicks.
Of course, to preserve one-to-one relationship between displays and messages it
could be argued that my observations indicate no more than that we have been
mistaken in regarding the long-call as a
single type of display—that we should
distinguish each of the syntactically separ-
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C. G. BEER
and "kek-kek" alarm calls all sound and
look (as sonagrams) so much alike that one
can only guess at what might have been the
kind of call from which a particular note
was taken. These notes go to make up
different kinds of signal utterance by being
combined, grouped, or repeated in different temporal patterns of cadence or
rhythm (Beer, 1976). The same distinction
can be made between the components of
postures and the postures they compose:
lifting of the carpel joints of the wings,
extension of the neck, tilting of the head,
spreading of the tail, sleeking of the feathers and so forth, each enter into several
display postures, which differ from one
another in their combination of these
components (c.f., Golani, 1976, who has
developed a notation for precise
spaciotemporal description of display
movements). Some patterns, such as the
head-toss, appear to serve as autonomous
displays when performed alone, and as
components of display when combined
with other patterns, as in the long-call, in
something like the manner of "but" and
"butter." Too little has been done to say
how far the analogy with linguistic structure can be pressed. All that we can say at
present is that Laughing Gull communicaLaughing Gulls vary the combinations tion appears to have some degree of
and sequences of their display behaviour hierarchical organization.
in ways that give the impression of being
systematic. For example long-notes and
If, for purposes of argument, we imhead-toss notes of the kind that occur in agine the linguistic analogy to apply in
long-calls can be performed by themselves; some detail to the Laughing Gull system,
the long-call itself forms part of a we do not thereby answer or simplify the
stereotyped sequence with other displays question "What is a display?" On the conin the courtship ritual described as the trary! We should have categories like
"greeting ceremony." Other examples words, phrases, clauses and sentences as
have been given elsewhere (Beer, 1975, options between which to choose in decid1976). Investigation and analysis have not ing what to call a display. The broad and
yet gone far enough to give more than the vaguely marked out field of reference that
impression that it is worth looking for display denotes at present will have been
syntactic rules affecting the "senses" in chartered in such detail as to entail narwhich displays or display components are rowing the meaning of the word to a
used and understood. But it is already particular syntactic grade, or giving it a
apparent that a distinction can be drawn generic sense covering the whole range
between minimum units of form and and so ruling out its use in the singular to
minimum units of sense, analagous to the refer to particular patterns of behaviour.
distinction between phonemes and morBut the conventions that can be imphemes in language. For example notes agined for dealing with the complexity
isolated from short-note strings of long- that appears to be emerging from study of
calls, copulation calls, "gackering" calls, the Communication behaviour of Laugh-
able forms to which a different kind of
message is attached and regard it as a
distinct kind of display. But this would be
to put principle before practice or perception. As yet our understanding of the
message content of Laughing Gull longcalls is top rudimentary and vague to serve
as a means of differentiating types of
long-call display. And such differentiation
into types would be at variance with, and
leave unaccounted for, the extent to which
formal features are shared between what
are referred to as long-calls, and give the
ostensive basis for use of the name in
descriptions of the behaviour of Laughing
Gulls and other species of gull. But
perhaps a more heuristic reason for taking
issue with this way to keep the semantics
simple—indeed with the general thesis
that displays attach to messages on a oneto-one basis—is that it inhibits consideration of the alternative possibilities that
there is some reason to believe might be
worth exploring in the syntactic domain,
for example the possibility that sequence
and combination rules may provide the
means for using one pattern of communication behaviour to convey more than one
kind of message.
WHAT IS A DISPLAY?
ing Gulls may also be thought of as having
limited applicability elsewhere. There are
groups of animals — I suspect that reptiles
and amphibia are of their number—in
which the variety of discrete communication patterns and what they communicate
are so limited as to make the conception of
one-to-one connection between displays
and messages sufficient to accomodate all
that goes on. In other cases, such as the
singing of many species of songbirds, the
variety in the communication behaviour
far exceeds what we reasonably assume to
be the variety in what there is to communicate about, and so appears to require more
than semantic considerations to account
for its generation. Evolution has apparently given rise to greater diversity among
communication systems than our available
equipment of descriptive concepts comes
fully to terms with. The effort to arrive at
once-and-for-all definitions for a set of
universal terms for description of communication behaviour runs into the
difficulty that generality entails lack of
precision and precision entails lack of generality.
The implications of this line of thought
are also less than obliging to that part of
comparative ethology that attempts to deal
with what can be called the phylogeny of
behaviour. The thesis that displays are
"derived activities" (Tinbergen, 1952),
evolved by "ritualization" from behaviour
having primary functions other than
communication, entails that certain behaviour patterns can be identified as
phylogenetically the same, if it is to be
applied and tested against evidence. The
notion of behavioural homology is as central to comparative ethology as the notion
of structural homology is to comparative
anatomy. But again ostensive criteria can
be distinguished from connotative definition. As I alluded earlier, the old Principle of Connections of St. Hilaire (Russell,
1916), according to which homology is
correspondence of relative position in
structures sharing the same plan, still provides the means of perceiving and deciding what is homologous to what in comparative morphology (c.f., Karten, 1969),
even though the textbooks now almost all
163
define homology in terms of descent from
common ancestral origins. In ethology
there is no exact equivalent of the Principle of Connections. Each of the possibilities, such as position in sequence, and
place in repertoire sets of behaviour patterns, turns out to be of limited application
and to admit of exceptions (Atz, 1970;
Beer, 1974). Similarity of form is probably
the most frequently used basis for recognizing behavioural homologies, but it too is
neither a sufficient nor a necessary condition, for there are formal similarities that
are interpreted as the result of convergence, and patterns of behaviour that
have been interpreted as homologous in
spite of having little similarity of form. In
the latter kind of case independent evidence of common origin is the basis of the
interpretation; but in other cases homology perceived as formal correspondence
of some sort is the basis for inference to
common origin. Given such want of consistency, and encouragement to circularity, it
is no wonder that a number of people have
argued that the notion of behavioural
homology is more a hindrance than a help
to clear thinking about the evolution of
behaviour (e.g., Klopfer, 1973a, 19736;
Hodos, 1970). Add to this the problems
that attend definitions of units of communication behaviour, such as display, and
one is tempted to declare the field of
behavioural phylogeny a trackless wilderness area, off-limits to scientific development.
Nevertheless there are small areas of this
field that have been cultivated with care
and consistency. Lorenz's (1940) comparative studies of duck displays, and the work
of Tinbergen (e.g., 1959) and Moynihan
(e.g., 1955) on the displays of gulls, are
classic examples of how the comparative
morphology approach to communication
behaviour has arrived at convincing accounts of behavioural evolution. Beginning usually from intuitively sensed perception of essential sameness in different
behaviour patterns, ethologists have deployed form analysis, situation analysis,
and sequence analysis (Tinbergen, 1959)
to back-up and make explicit the grounds
for viewing the behaviour as homologous
164
C. G. BEER
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