some complexities in the communication behavior of gulls

SOME COMPLEXITIES IN T H E COMMUNICATION BEHAVIOR OF GULLS*

Colin Beer Institute of Animal Behavior

Rutgers University Newark, New Jersey 07102

This article returns to a theme that I tried to develop once before’: the place of preconceptions in the study of animal behavior. Here, however, I shall focus the discussion more narrowly, concentrating on aspects of my own work on the communication behavior of laughing gulls (Lams arricilla).

But first, some general preliminaries. According to Chomsky 2:

Each known animal communication system either consists of a fixed number of signals, each associated with a specific range of eliciting conditions or internal states, or a fixed number of “linguistic dimensions,” each associated with a nonlinguistic dimension in the sense that selection of a point along one indicates a corresponding point along the other. In neither case is there any significant similarity to human language.

At least until recently, this statement was consistent with the published research on animal communication. Nevertheless the ideas that informed this research and governed its interpretation have changed as the facts have accumulated, and the changes have been in the direction of recognizing greater and greater complexity in animal communication.

I f we begin with the work of the ethologists in the period when instinct was their ruling concept we find animal communication treated as though it consisted of sets of lock and key combinations. The signals-postural displays, vocalizations, and so forth-were described as social releasers because they were thought to engage, on a one-to-one basis, “innate releasing mechanisms” in the recipient individual, thus opening the way to the flow of accumulated instinctive excitation into pathways governing a specific social response, thereby causing its performance. Being parts of instinctive systems, the releasers and innate releasing mechanisms had to correspond to one another as species characteristics; hence little or no consideration was given to the possibility of individual differences or individual recognition in animal social interactions. Even in the study of imprinting the matter was viewed as the means by which an animal gets tuned to the features of its kind, rather than as the means by which one individual gets socially attached to other individuals.

Observation showed the social interactions of animals to be less predictable than they should be according to instinct theory. The instinct theory allowed for variation in intensity of response, as a consequence of variation in intensity or completeness of the releaser and variation in level of internal excitation. But the observations also showed variation in kind of response, and this was not according to theory, except for the special case of what was called “displacement activities.” So the journal

*Research reported in this paper was supported by Grants GM 12774 and MH 16727 from the United States Public Health Service. The United States Fish and Wildlife Service granted permission for the work to be carried out in the Brigantine National Wildlife Refuge, and made available a building in the Refuge for the use of the project. The cooperation and hospitality of the Refuge Manager and his staff are also gratefully acknowledged. This is publication U226 from the Institute of Animal Behavior, Rutgers University.

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414 Annals New York Academy of Sciences

articles became populated with flow diagrams representing sequence patterns and their relative frequencies by curving arrows of differing thicknesses. Instead of being obligatory, the sequence combinations were seen to be probabilistic, and the analysis of social interactions became statistical. We became used to having the behavior dispersed in transition matrices and described in terms of stochastic processes and quantities of information or uncertainty. To more simple-minded persons, like myself, howeyer, it was not always clear what all the numbers meant or where they were leading. We seemed to be getting sophisticated quantitative descriptions of the “what” of animal communication, but not much understanding of the “how” and “why.”

Some help came with the discovery of the significance of context in animal communication. W. John Smith’s4 saw how context could make sense of some of the complexity in the interaction sequences of the tyrranid flycatchers he had been studying. Independently and a t about the same time, the same point was perceived by G. H. Manley in a study of black-headed gulls (Larus ridibundus) in England, but his work remains unpublished. The point is that signals are not self-contained transmissions; they arrive in a setting or frame, which can include the state or status of the receiver, and this contextual accompaniment can affect what a signal signifies to the receiver. For instance, the song of a territory-holding male songbird signifies threat to another male but sexual invitation to an unmated female; and the call that sounds alarm when given by a laughing gull inside the gullery announces discovery of food when given outside the gullery. Smith used the semiotic scheme of Charles Morris5 to develop his conception of communication, as qualified by context, into a comprehen- sive approach to social communication in general. What is encoded in a signal by its sender he called the “message” of the signal; this he considered to be an internal state conducive to some particular action or actions, the state probably being the same for all transmissions of the signal. The response to the signal he called the signal’s “meaning,” which is determined jointly by the signal itself and the context. Since the context can vary, so too can the meaning of a signal, even though the message of the signal may be the same in all contexts.

Manley’s version of the role of context in animal communication was slightly different from Smith’s. He wrote of “context interpretations” when referring to the variations in response to a signal that Smith had described as differences of meaning. But he also argued that there is “context determination” by which he meant that the same signal could be used to encode different information on different occasions by being assembled with different contextual accompaniments. The contextual accompaniments to which Manley paid most attention were the details of such features as posture and orientation with which a signal was given, and the other behavior performed by the signaler before and after the signal. Thus, according to Manley, the so-called “upright” posture of the black-headed gull expresses a conflict state between tendencies to attack and to flee when performed with head-on orientation in a n agonistic context in which attacking and fleeing are the actions most likely to occur in sequence with it; but when performed in a sequence that goes “oblique-and-long-call, forward, upright, head-flagging,” with parallel orientation to a female, it expresses the motivation of pair-formation. So, in Smith’s terms, Manley would say that the same signal can be used to encode different messages by varying the context in which it is presented, whereas Smith would say that the same signal probably always encodes the same message irrespective of context.

The difference here could perhaps be resolved by removing some of the vagueness about what is to count as a signal. If signals were demarcated on the basis of messagecarrying function, the isolated upright of the gulls could be considered as one kind of signal and the whole sequence “oblique-and-long-call, etc.” as another and different

Beer: Communication Behavior of Gulls 415

kind of signal, for example. This would preserve uniqueness of signal-message couplings, as Smith would have it, a t the same time as allowing Manley’s point that morphologically the same bits of behavior can be put to different expressive uses. However, this move runs into the difficulty that we often have to make our judgments about what the distinct displays, vocalizations, and so forth are, on the basis of what strikes our eyes and ears as distinct and consistent patterns, long before we have any understanding of the message or meaning content that attaches to them. There is also the drawback that the possibility of compound signals, and hence compound messages, is, if not ruled out, at least made unlikely to occur to the thinking that would make the lines round signals coincide with the lines round messages. To one less committed to a belief in the uniqueness of signal-message coupling, the possibility of compound messages does not seem unlikely, indeed is given substance by example. To take perhaps the simplest, there are cases in which it appears that what is expressed by a certain signal in one context is negatively expressed in another context by presentation of the signal in concert with qualifying behavior. For instance, the upright of the gulls expresses hostility in agonistic contexts, and may carry the same message in a courtship context where, however, its being followed immediately by the posture called “facing-away” appears to negate the message of hostility. Constancy of message for a signal in different contexts is thus not incompatible with the idea of compound messages; indeed, as in this case of the upright of gulls, it may be necessary for some kinds of compound message. In other cases, however, there appears to be considerable semantic flexibility in the use of signals by animals, instances of which I shall come to shortly.

In the meantime 1 return to the theme of preconceptions. Why should the complexity of animal communication behavior, including the possibility of semantic flexibility of the kinds 1 think we now have to consider, have gone so long without getting attention from ethological investigators? Part of the answer is that research has to wait on advances in technology in some areas, and some of the complexity with which we now have to deal in animal communication studies has only recently become apparent through the use of machinery that was not available earlier. But a t least equally important influences have been the bogey of anthropomorphism and Lloyd Morgan’s solution to it, as well as the more general constraints imposed by deterministic and reductionistic ways of thinking on what is regarded as admissible as explanation in science. The prevalent conception of the an iqa l is still the Cartesian one of a causally determined machine in which the human.attributes of intention, reason, and so forth are excluded. With the invention of machines like guided missiles we can now talk comfortably about animals as goaldirected in their behavior; and computer technology has opened up reaches of analogical possibility the exploration of which has only begun. Nevertheless, I suspect that many of us still suffer a twinge of scientific conscience when we catch ourselves attributing intention or subjectivity to the actions of a n animal.

To think of a n animal as a machine is usually to see its behavior as emitted movement or elicited response. In either case, causal mechanisms will be assumed and sought, as they have been in physiology and ethology, and the conception of the animal as an active agent using action in the pursuit of ends will probably not even come to mind. The idea of use here entails the notion of intention, and this is too mentalistic a notion for most behaviorists, even though, as Charles Taylor6 has pointed out, they sometimes unwittingly imply it in the forms of their descriptions. Hence the suggestion that an animal might use the same signal to express different messages, by varying what accompanies or occurs in sequence with it, has a heretical taint and so will not occur to the minds of the pure in science, o r will be shunned as a threat to salvation in causality. Moreover, the suggestion has a suspicious resem-


blance to a description of language, and the serious will agree that anyone who thinks animals can talk is lost in a Disneyland of whimsies.

It seems to me, however, that neither causal nor stochastic conceptions have come to close grips with the complexity that now appears to exist in the communication behavior of some species. In the short run at least, other sets of preconceptions may be more likely to prove heuristic. In what follows I shall illustrate some of the forms of complexity with examples from the laughing gulls, and shall suggest that some analogies from language might be useful in making at least preliminary sense of them.

MARGINS OF MEANING

The vocal repertoire of a mature laughing gull contains about twelve distinguishable calls-distinguishable, that is, on the basis of how they sound to our ears and how they appear to function in the social behavior of the gulls. Some of the calls grade into one another; most of them are quite distinct from one another.

Sonagrams of these calls show them to be made up of notes of a small number of types, distinguishable on the basis of duration and “shape,” some of which occur in more than one type of call. If one were to take scissors and cut out a note from sonagrams of the short-note part of a long-call, a gackering call, a copulation call, an alarm call, and a food-finding call, the similarity of form would be found to be such that reassigning the notes to the kinds of call from which they came would turn out to be a game of chance, especially if all the calls had been recorded from the same bird (FIGURE 1). This is one illustration of Manley’s point that morphologically the same bits of behavior can be put to different expressive uses by being strung together in different ways.

It can be objected that sonagrams abstract only certain features of a sound, and hence that distinguishing features in the notes selected might have escaped represent- ation in my guessing game. It is well known that there is often considerable disparity between how similar or different two voices sound to our ears and how similar or different the sonagrams of these voices look to our eyes. However, the sounds uttered by gulls appear to be much simpler in form than are the sounds uttered by people, and consequently the sonagrams show much cleaner patterns of frequency modulation, frequency spectra, and temporal partitioning. These together with amplitude modulation are the only obvious parameters for comparison.

I claim, then, that one can draw a distinction, in the vocal productions of laughing gulls, between the minimum units of sound used and the minimum units of sense, in something like the way in which one distinguishes between phonemes and morphemes in language. The minimum units of sound are notes, of which there are perhaps six recognisably distinct kinds. Some of these, such as the disyllabbic “ke- hah” note and the “head-toss note,” are also minimum units of sense. That is to say. they serve as signals even when uttered by themselves, singly. But most notes contribute to communication by being strung together, either in repetitions of the same kind of note, as in the copulation call (FIGURE I ) . or in combination of more than one kind of note, as in the long-call (See FIGURES I , 3,4,5). Where different call types have the same note type the difference between the call types is in the number of repetitions of the note-for example alarm calls consist of only two or three short notes of the type that occurs in indefinitely long strings in gackering and the copulation call-or in temporal patterning of repetition or the amplitude contours. as distinguish the copulation call, in which notes of equal duration and loudness are


repeated at a constant rate, from gackering, in which the notes vary in duration and loudness and are unevenly spaced.

The communication behavior of laughing gulls consists of more than calls, however; the birds also use posture and movement in displays, most of which accompany a call of one or more types. The distinction between units of form and units of sense can also be applied in analysis of the displays. For example, lifting the carpel joints of the wings away from the sides of the body is a component of most of the display types. It does not occur by itself-that is without being accompanied by any of the other component types-and would presumably be meaningless as a signal if i t did. The head-toss movement, accompanied by the head-toss call, does occur by itself as a signal. as well as being the terminal component of most longcalls. The communication system of laughing gulls can thus be viewed as a limited number of basic vocal and postural elements, which can be assembled in combinations and sequences to form message carrying patterns or signals.

This hierarchical scheme should not be too hard to entertain. It is, after all, the sort of scheme we take to apply to motor patterning in general. On the bottom tier are the basic movement possibilities, consisting of all the flexions, extensions. adductions. abductions and so forth that the body has available to it. Then there are the combinations of these into functional patterns of movement, such as running. punching, kicking and so forth. Thirdly, there is the combining of movements into actions, such as attacking, fleeing, avoiding, searching, and so forth. And finally, if we go along with Miller, Galanter and Pribram,’ there are the combinations of actions in the realizations of plans, as in building, courting, cooking, and so forth. I have not yet come to complexity in my gulls that cannot be accommodated within the bottom two levels of this scheme. The longcall may necessitate adding a third level to the communication hierarchy however, for it appears to serve for the composing of compound messages.

A FRAME FOR MEANING

The longcall of the laughing gull is what gives the bird its name. It consists of a string of notes, short and quick at the beginning, and then longer and slower, which it is not hard to hear as rather derisive laughter. The call is also the most complicated in the laughing gull repertoire, both in its structure and in its use.

Structurally the longcall can be divided into a t least three sections, which I refer to as the short-note section, the long-note section and the head-toss section. The short-note section consists of between 2 and 15 brief and rapidly uttered notes; the long-note section consists of between I and 12 notes that are about twice as long as those of the short-note section and spaced farther apart; and the head-toss section, which may be omitted, consists of between I and 8 notes slightly shorter than the long-notes and variably spaced. Sonagrams of typical examples of laughing gull long-calls are illustrated in FIGURES I , 3,4, and 5. Strings of long-notes and head-toss notes can occur without preceding short-notes, and in isolation from one another. Frequently a string of long-notes precedes as well as follows the short-notes. And even further variation is added with the varieties of posture in which the notes are uttered.

Longcalls are given on the wing, while swimming or floating, and while sitting. but I shall more o r less restrict my comments to what is perhaps the commonest case: a bird standing on the ground. Such a bird gives the short-note section in the full “oblique” posture: body more o r less horizontal, neck fully extended a t an angle of


about 45’ to the body with the head more or less horizontal; the mouth is widely open, the carpel joints of the wings held out from the sides of the body, and the contour feathers are “sleeked”-pressed down close to the skin surface (FIGURE 2a). In some situations the body axis may be tilted upwards at the front, even as much as 45”. the head pointing upwards at the same angle. In other situations the bill may be pointed slightly downwards. In the long-note section the oblique posture may be maintained with little change, apart from some reduction in the extension of the neck and degiee of lifting of the carpels. More commonly, the neck is maintained at full stretch and the angle changed so as to lower the head towards being in line with the body. Typically the head is lowered a little with each long-note. Consequently, long long-note sections end up with head, neck and body all in line (FIGURE 2b). Head- toss notes are accompanied by head-tosses: rapid backward flexing of the neck and upward jerking of the head, which can be so vigorous as to bring the top of the head into contact with the back of the body (FIGURE 2c). The movement can be kept to little more than a flick of the bill, however, and one even hears head-toss notes unaccompanied by any head-toss movement.

The range of situations in which the longcall occurs covers almost all the distinguishable classes of social interaction. Early in the breeding season it is used by males in much the same way in which male songbirds use song: to threaten other males that might challenge territorial claims and to advertise mating availability to unmated females. During courtship, the longcall is the first display in the sequence of displays referred to as the “greeting ceremony,” which both birds of a pair go through side by side and more or less in unison. After laying, when the birds of a pair take turns at incubating the eggs, longcalls may be exchanged at nest relief. Incubating gulls will also longcall at neighbors and strangers. During hatching of the eggs, gulls sometimes look as though they are longcalling to their pipping eggs or newly hatched young. After the chicks have reached the age of about eight days post- hatching it is quite definitely the case that the parents direct long-calls at their chicks, particularly just after returning to the home site if the chicks are some distance away. A gull will also longcall at chicks other than its own, both at home and away, and this calling is usually followed by the gull’s attacking the chicks. Outside the gullery, longcalls are given’by roosting gulls to others flying overhead, by a gull that has just displaced another from its perch, by what usually turns out to be the dominant gull in scrambles over food, and by gulls flying in flocks. This list could be added to and refined by the drawing of finer distinctions of context and sequence.

Some of the variations in the longcall are associated with differences of use or context. For example, the longcalls with the longest strings of long-notes and marked holding of the low horizontal posture are those given during courtship by a bird landing beside its potential mate, especially if the birds have been apart for a spell. Incubating gulls, on the other hand, typically have abbreviated long-note sections and do not lower the head from the oblique position, at least if the call is being given to a bird other than the mate.

Other variation in the calls cuts across contexts, however. If one spends a few hours a day in the same part of the gullery for several days one learns to recognize some of the gulls individually by ear, most easily by individual characteristics of the longcalls. The pitch and timbre qualities of the calls differ between individuals, but even more distinguishing are the number and rate of repetition of notes in the short- note section. The sonagrams show the frequency modulation shapes of the short- notes also to be characteristic for an individual and different between individuals (FIGURES 3 and 4). At one extreme are gulls that give only one or two relatively long short-notes; at the other extreme are gulls that rattle off fifteen or so very short short- notes in rapid succession that suggests machine-gun fire. There is correlation between

Beer: Communication Behavior of Gulls 42 1

FIGURE 2. Long-call postures of the Laughing Gull a. Full oblique, in which short notes are given; b. Low horizontal posture at the end of a long long-note section; and c. Head-toss.


number of notes, duration of note, and rate of repetition, but it is far from perfect. Some gulls have a short-note section in which the notes differ in length, giving a broken rhythm to the sequence (third down in FIGURE^). Whatever the pattern for a particular gull it varies very little from context to context or from one part of the breeding season to another (FIGIIRE 3). The short-note section appears to be, so to speak, the signature tune of a gull’s longcall, announcing a t the outset the identity of the individual making the call.

Do the gulls hear it this way? I have done a number of playback experiments that show that they do. Plajing a recording of the longcall of the mate to a gull sitting on its nest elicited calling in reply, standing up as though to make way for nest relief, and, in some cases, even departure from the nest. To a similar recording of a neighbor gull, or a gull from a remote part of the gullery, there was no response at all.8 The lack of response here does not mean that gulls cannot distinguish the longcalls of neighbors from those of strangers. From the ways they react in normal circumstances it appears that they probably d o make such discrimination, ignoring the neighbor when they would call at a stranger. That the neighbor and stranger playback calls elicited no response could have been due to the fact that they did not occur in a context that required any action, whereas the call of the mate had the nest relief context waiting for it. In any case the experiment made it clear that a gull can recognize the longcall of its mate.

Playback of longcalls of parents to chicks in a testing arena indoors produced what to me were even more interestin4results. Very young chicks-less than 48 hours post-hatching-showed discrimination between long-calls of their own parents and longcalls of a neighbor, but it was in negative rather than in positive response: they tended to be silenced and to be driven away and into defensive crouching more by a neighbor’s call than by the parent’s call. They showed strong positive response- approach, vocalization, etc.-to playback of the “crooning” call-the call with which parents accompany their offering of food to their chicks-and n o discrimination between the crooning of the parent and the crooning of the neighbor.8.9 In a recording containing both crooning calls and long-calls, the positive response to the crooning overrode the negative response to long-calls, even for calls of the neighbor. Chicks tested in the same ways at two weeks post-hatching behaved differently. They still showed negative reaction to longcalls of a neighbor, but to longcalls of the parent they almost all showed strong positive response. To crooning, whether by the parent ‘or by a neighbor, they made no response whatever. At this age crooning by itself can no longer induce the filial approach behavior that it was sufficient to command when the chicks were nestlings.

Crooning is the only call that a parent uses a t all obviously to direct the filial behavior of its nestlings. The parent does give long-calls when in the company of its nestlings, but these calls appear to be directed not a t them but a t adults. By the time the chicks are two weeks old, however, the parents begin directing other calls, including longcalls a t them. The longcall, as I have said, is used particularly when the chicks are out of sight or a t a distance from the home place, which is often the case when a parent returns after a spell away. At least part of the reason for the longcall’s taking over part of what was the job of crooning appears to have to d o with the fact that the longcall enables individual recognition by ear but the crooning does not. By the time the chicks are two weeks old their social world has enlarged to include adults other than the parents, and to approach such adults is to run the risk of abuse that can be so severe as to be lethal. The longcall provides the means by which a chick can recognize its parent individually from a distance and when the parent may be out of sight, and so keep its approaches for the only adults that will treat it with parental care.

Beer: Communica t ion Behavior of Gulls 427

But a laughing gull chick, two weeks old and more, does not approach in response to every longcall by one of its parents. This fact was brought home to me unexpectedly in a series of tests in which response to playback of the parent's longcall was very strongly positive for all the chicks except two. and these two were in such marked contrast to the rest that I looked for something special in the circumstances of their testing. They turned out to be the only ones for which I had used recordings made when they were nestlings, the other chicks having been tested with recordings made on the day of testing or the day before. I then deliberately tested two-week-old chicks with recordings of their parents' longcalls made when they were nestlings and made at the time of testing. These chicks also showed little or no response to the earlier calls, but responded strongly and positively to the later calls. Nevertheless there were indications that the chicks recognized the earlier as those of their parents, for they did not show the negative response to them that they showed to some of the longcalls of neighbors that were played to them. There are several possible explanations for the discrimination between the earlier and later calls, but the one that I favored was that a parent gull uses a version of the long-call when addressing its chicks that is different from the version or versions it uses when addressing adults. As I have already mentioned, a gull with nestlings appears not to direct longcalls towards them, but a gull with two-week-old chicks does direct some of its longcalls a t its chicks, the rest being directed at adults or foreign chicks. In selecting recordings to use in the tests of older chicks I had probably unwittingly chosen mostly calls directed at chicks, for these are more likely to be clear of interference from other calls being uttered at the same time than are calls directed at adults. In any case, I ran another series of tests in which I compared the responses of older chicks to playback of longcalls that the parents had directed a t them in the field, and to playback of longcalls that the parents had directed at adults, both sets of recordings having been made at the time of testing. Again the chicks showed discrimination: their responses to the calls that had been directed a t them were stronger than their responses to the calls that had not.9

How did these chicks know which call was which? My initial supposition was that the messagecarrying part of the longcall is in its last two sections. the short-note section being merely the individually identifying introduction. 1 failed to find any consistent difference between the two classes of call in the long-note and head-toss note sections, however. Contrary to my expectations, the differentiating characteristic turned up in the amplitude modulation of the short-note section; .in the chick- directed calls the first one or two notes were louder than those followirig, whereas in the adult directed calls the first one or two notes were softer than those following, or there was a steady increase in loudness from note to note in the string (FIGURE 5) . 1 had difficulty believing in this result until I returned to the gullery and listened for the difference. Then it stood out so distinctly that I marveled at how blind perception can be.

1 am far from a full understanding of how the laughing gulls use their long-calls. Already, however, two points are clear. Firstly, utterance of a long-call conveys more than one kind of information: the caller identifies itself and it transmits a message which is of the nature of a warning, a command, an invitation or an advertisement. Secondly this message can be varied on different occasions of use of the long-call, through variation of features internal to the call. The identification can thus be coupled with a variety of other information; in this sense the long-call can be considered as conveying compound messages. Again, however, we have the question of what should count as a distinct signal or display; in this case should it be the utterance form that we refer to as the long-call or the distinguishable messagecarrying versions of it. At present we are unable to say how many different message


carrying versions there are or what distinguishes them. In any case, it is convenient, especially for comparative purposes, to go on speaking of the long-call as the display entity. But from the evidence of multiplicity in the ways in which it is used, its semantic versatility, 1 think it is more accurate to think of it as something like a syntactic form or framework, rather than as a display in the sense that it is fixed in either of the ways described by Chomsky in the statement I quoted at the beginning.

49 I

I 49

0 Lc I-

‘1.0 ‘2 .o ‘3.0 TIME ,SECON DS

FICLJRE 5. Amplitude-time sonagrams (wide band) of longcalls of three gulls, illustrating the difference between calls to adults (above) and calls to chicks (below).

I t is very likely that variation of external features, in addition to variation of internal features, contributes to the variety of message that can be encoded in longcalls or for which longcalls can be used to encode. This raises the possibility of compound messages of more complex types than those that can be contained within the longcall; but an even more promising display for realizing this possibility is facing-away.


FIGURE 6. “White” facing-away.

MEANING IN MASKING

Facing-away, or “head-flagging” as it was originally called,IO is a display, or component of displays, shown by gulls, in which the bird turns its head to look in the direction away from the other towards which it is displaying. In so doing it removes its bill, eyes and, in those species possessing one, the mask or hood from the view of the other bird. It is most typically performed in the posture known as the upright in which the neck is extended vertically upwards, with the head more or less horizontal and the carpel joints lifted; but, a t least in the laughing gull, facingaway can also be superimposed on most of the other display postures as well. I shall restrict my comments to facing-away in the upright. In the laughing gull this display occurs in two forms. In one the dark hood is completely hidden from behind, the margin of the hood being pulled into a more o r less vertical line and the feathers behind it being raised to form a shielding ruff (FIGURE 6). In the other form, part of the hood is still visible from behind, the margin being kept more or less horizontal and the feathers being flattened so that even the white tufts just above and below the eyes are kept on show (FIGURE 7). There are intermediates between these two extremes, and a bird can

FIGURE 7. “Black“ facing-away.


shift from one to the other during performance of the display; but the transitions are usually rapid, occupying considerably less time than is spent holding in either of the contrasting forms, which 1 refer to as “white” facing-away and “black” facing-away.

Three alternative functions have been suggested for facing-away in gulls: 1. appeasement of a hostile opponent; 2. allaying of fear in a mate or potential mate; and 3. “cut-off’ of visual stimulation liable to cause the displaying bird to attack or flee, in situations in which either action would be against the displayer’s interests.” The first two suggestions assume that the frontal aspect of the head presents a provoking or threatening appearance, the turning away of which reduces the probability of either attacking or fleeing by the other bird. Cut-off is supposed to work in the same way for the displaying bird.

M y first guess a t why there should be two forms of facing-away in laughing gulls was that the black form provides a way of effecting cut-off at the same time as keeping part of the hood visible to convey threat, while the white form provides cut- off and the canceling of threat. From this it should follow that black facing-away belongs in agonistic contexts-those in which the aim is to drive the other bird away-and that white facing-away belongs in contexts in which the aim is to keep the other bird from leaving, as in courtship. Laughing gulls show facing-away in both agonistic and courtship contexts, so, as a first test of my interpretation. I compared numbers of occurrences of the two kinds of facing-away in these two kinds of situation. The agonistic encounters were according to expectation: most of the occurrences of facing-away were of the black sort. Courtship encounters did not conform, however: occurrences of facing-away were about equally divided between the two forms. I then looked a t the behavior of the displaying bird immediately after facing-away. Again the two contexts showed differences that were different from expectation. In the agonistic sequences, a bird facing-away in the black form was likely either to attack or to flee immediately afterwards. The few showing the white form in this situation, with some exceptions that I shall come to directly, fled when attacked but did not themselves attack, the hostility coming from birds to which the displaying bird faced-away while approaching its nest. The evidence from agonistic encounters suggests that in this context a gull uses black facing-away for cut-off combined with threat, and white facing away as appeasement. In courtship sequences attack was infrequent; when it did occur following facing-away it was most often from the white form (in contrast to what was the case in the agonistic encounters). Black facing-away was most often transitional to leaving, usually by flight. After white facing-away the two birds of a courting pair usually went on performing courtship behavior or stood quietly side by side preening. The evidence from the courtship encounters suggests that in this context both forms of the display signify lack of hostility, black facing-away indicating a tendency to leave, thus warning the other bird not to press its suit too vigorously, and white facing-away indicating that the bird will stay and is strongly attracted to the other. In the incubation period facing-away occurs a t nest-relief, when abbreviated versions of the courtship ritual are often performed. Then the relieving bird, the one that will stay, typically does white facing-away, and the relieved bird typically does black facingaway just before flying. Thus the two birds continue with a difference the pattern of the courtship period.

Courting gulls frequently become involved agonistically with a third. A common sequence in this mixed situation consists of one of the courting birds, usually the male, launching an attack on the outsider and facing-away to its partner as it does so. lnvariably this facing-away is in the white form, and is thus apparently an exception to the rule that white facing-away in agonistic encounters signifies lack of hostility. But in this situation the display is not directed a t the opponent, but a t the courtship

Beer: Communica t ion Behavior of Gulls 43 1

partner, and appears to have the function of indicating to the partner that the manifest hostility is directed elsewhere. As in the pure agonistic situation, therefore, the white facing-away signifies lack of hostility to the bird towards which it is directed; but the total motivation of the displaying bird is obviously different in the two situations, being low in attack tendency in the one case and overtly expressing attack tendency in the other.

There are "family resemblances" between the uses of facing-away in the different contexts in which the display occurs in the social behavior of laughing gulls, but it does not appear to be the case that the underlying motivational states can be the same across all these contexts. But if the same display can express different motivational states in different contexts is there not the possibility that the bird displayed to will be confused or misled. particularly if the contexts grade into one another or overlap, as d o agonistic and courtship contexts? Mistakes d o occur in the social interactions of laughing gulls. but their probability is apparently kept low by the fact that when facing-away occurs in courtship it is very often in sequence with specific other displays, the order of which is quite stereotyped. This is the sequence I referred to earlier as the greeting ceremony. Such regular sequential patterning is lacking in the occurrences of facing-away in agonistic interactions. As Manley observed, the context that can qualify the meaning of a display can include the other displays in sequence with which it occurs and so provides the displayer with a way of using the same display to express different messages. And even when the message of the display might be the same across contexts, as in the use of white facing-away in the pure and mixed agonistic situations, the accompanying behavior makes it possible for the display to be used to express different compound messages. Again. of course, one could argue about where to draw distinctions between functional categories in the communication system. and what the most appropriate terms for these categories might be. But however we divide and describe in this matter of the communication behavior of gulls I think we have to d o with a complexity that the instinctivist, behaviorist or stochastic conceptions of animal behavior overlook and d o not provide for, and which does not conform to either of the systems described in the quotation from Chomsky.

CONCLUSION

I suspect that the relevance of my gull studies to the theme of this conference, the origins and evolution of language, is, if anything, only of a rather negative, indirect and unspecific sort. Perhaps the most general point that my work illustrates is that the more that animal communications behavior is studied the more complex it tends to turn ou t to be. So when animal work is used to make comparative points in discussions of language I should advise being tentative about it, lest tomorrow's discoveries make today's conclusions look silly.

In part, the recognition of the greater complexity has resulted from, and in turn caused, changes in preconceived views about animal communication, including the models in terms of which animal communication has been thought about. At least in my own case, linguistic analogies have, to some extent. taken the places previously occupied by causal and statistical models. At least for the time being I d o not think, as I have no doubt some others do, that this is a retrograde step. On the contrary, the study of language is so far ahead of the study of animal communication that it should not be surprising if linguistics has more to offer the animal studies than vice versa. N o t that the analogies are very tight. I realize that when I talk of the syntax of gull communication I have to be understood as using the word in a sense that excludes


much of what it connotes in its linguistic context. We cannot, for example, parse a sequence of gull signals in any precise sense, a t least not yet. But I doubt whether I should be looking in that direction at all if 1 had kept to the views seen through the lenses of social releasers and transition probabilities.

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