Search

Several laboratory studies have revealed functional hemispheric lateralization in birds performing visual tasks. However, the role of functional brain asymmetries in spatial behaviour in natural settings is still poorly investigated. We studied monocularly occluded homing pigeons, Columba livia, to investigate potential differences in the hemispheric control of navigational performance. We GPS-tracked monocularly occluded and control binocular homing pigeons during seven group training releases and a final solitary release from each of two sites. The pigeons were then given one last release from each site after a phase shift of the light-dark cycle under binocular conditions, to distinguish compass-based orientation from landmark-based pilotage. Overall, pigeons homing with the left eye/right hemisphere (RH) displayed a greater fidelity to the familiar space previously experienced than pigeons homing with the right eye/left hemisphere (LH). Another difference between the two monocular groups is that LH pigeons were more likely than RH pigeons to fly with other pigeons during the group training releases. The data support the hypothesis that the left eye/right hemisphere plays a more substantial role as pigeons develop fidelity to certain routes to home from familiar release sites, an enhanced fidelity that may be supported by superior memory for familiar landmarks.

Despite decades of interest, the adaptive significance of the extraordinary diversity in the design of animal signals remains elusive. It is suggested that signal design consists of two components: ‘strategic design’ and ‘efficacy’. Strategic design is concerned with how a signal is constructed by natural selection to provide the information necessary to make a receiver respond (e.g. by being good at displaying underlying quality), whilst efficacy is concerned with how a signal is designed to get that information across to the receiver (e.g. by being easily measured). It is argued that an important but neglected evolutionary force on animal signals is therefore the psychology of the signal receiver, and that three aspects of receiver psychology (what a receiver finds easy to detect, easy to discriminate and easy to remember) constitute powerful selective forces in signal design. Greatest emphasis is given to memorability because this has been least considered by previous authors. It is argued that learning and memory are involved in a wide range of signals, and numerous hypotheses as to how signals may be adapted to be more memorable to receivers are suggested. The relationship of this analysis to earlier attempts at understanding signals is explored, particularly with reference to the concepts of honesty, manipulation and mind-reading.

The \`design' of any animal signal is affected by at least three selection pressures: (i) the type of information being conveyed (the message); (ii) the transmission properties of the medium; and (iii) the sensory and psychological properties of the receiver. We describe a field study of the bluehead wrasse (Thalassoma bifasciatum) and examine the \`circling' display of the male in the light of these three pressures. Analysis of videotape records of the display shows that it carries accurate information about when a spawning dash will occur. The speed with which the pectoral fins are moved increases steadily over the 10 s before spawning so that the exact time of spawning can be predicted. Dark spots (not present when the male is chasing other males) appear on the ends of the pectoral fins and may `amplify' perception of fin movements. The colour change shown by the male when chasing other males and when courting females was measured in situ by using Munsell colour charts, and was subsequently converted to dominant wavelength and excitation purity equivalents. The circling display appears to be designed to convey information about intention to spawn to a female that is relatively close whilst not conveying this information to other males that are further away.

Animal communication is studied both by neurobiologists and by evolutionary biologists, but in very different ways. The purpose of this article is to show how both groups could benefit from a greater appreciation of each other's approach. Evolutionary biologists should take more account of the role played by the sensory systems and brains of receivers in constraining the design of animal signals. Neurobiologists should be more aware of recent advances in the understanding of signal—receiver co-evolution and the evolutionary origins of animal signals. A series of recent examples are cited that illustrate how pre-existing neurophysiological or psychological properties of receiver organisms are essential to our understanding of the design characteristics of animal signals and of their origins. Also discussed are a number of other areas of signalling in which the study of ‘receiver psychology' is likely to be fruitful.

The warning signals of toxic insects are often 'multimodal', combining bright coloration with sounds or odours (or both). Pyrazine (a common insect warning odour) can elicit an intrinsic avoidance in domestic chicks Gallus gallus domesticus, both against novel coloured food, and also against food colours that are specifically associated with aposematism, namely yellow and red. In three experiments, we investigated the role of novelty in this innate bias against yellow coloured food in the presence of pyrazine. Naive chicks were familiarized either to pyrazine odour or to coloured food before being tested for a bias against yellow (warningly coloured) food as opposed to green (nonwarningly coloured) food. In experiment 1, pyrazine novelty was shown to be vital for eliciting a bias against yellow food. However, experiment 2 suggested that colour novelty was not important: chicks familiarized with coloured crumbs still avoided yellow crumbs when pyrazine was presented. In a third experiment that gave chicks an even greater degree of pre-exposure to coloured crumbs, the bias against yellow food eventually waned, although pyrazine continued to elicit an aversion to yellow even after birds had had experience of up to 24 palatable yellow crumbs. Pyrazine novelty has been an important pressure in the evolution of multimodal warning signals, and can continue to promote the avoidance of warningly coloured food, even when it is relatively familiar. The implications for warning signals are discussed. Copyright 1999 The Association for the Study of Animal Behaviour.

SUMMARYProviding homing pigeons with a 5 min preview of the landscape at familiar sites prior to release reliably improves the birds' subsequent homing speeds. This phenomenon has been taken to suggest that the visual panorama is involved in familiar-site recognition, yet the exact nature of the improvement has never been elucidated. We employed newly developed miniature Global Positioning System (GPS) tracking technology to investigate how access to visual cues prior to release affects pigeons' flight along the length of the homing route. By applying a variety of novel analytical techniques enabled by the high-resolution GPS data (track efficiency, virtual vanishing bearings,orientation threshold), we localised the preview effect to the first 1000 m of the journey. Birds denied preview of a familiar landscape for 5 min before take-off flew an initially more tortuous path, including a high incidence of circling, possibly as part of an information-gathering strategy to determine their position. Beyond the first 1000 m, no differences were found in the performance of birds with or without preview. That the effect of the visual treatment was evident only in the early part of the journey suggests that lack of access to visual cues prior to release does not result in a non-specific effect on behaviour that is maintained throughout the flight. Instead, it seems that at least some decisions regarding the direction of home can be made prior to release and that such decisions are delayed if visual access to the landscape is denied. Overall, the variety of approaches applied here clearly highlight the potential for future applications of GPS tracking technology in navigation studies.

For animals that travel in groups, the directional choices of conspecifics are potentially a rich source of information for spatial learning. In this study, we investigate how the opportunity to follow a locally experienced demonstrator affects route learning by pigeons over repeated homing flights. This test of social influences on navigation takes advantage of the individually distinctive routes that pigeons establish when trained alone. We found that pigeons learn routes just as effectively while flying with a partner as control pigeons do while flying alone. However, rather than learning the exact route of the demonstrator, the paired routes shifted over repeated flights, which suggests that the birds with less local experience also took an active role in the navigational task. The efficiency of the original routes was a key factor in how far they shifted, with less efficient routes undergoing the greatest changes. In this context, inefficient routes are unlikely to be maintained through repeated rounds of social transmission, and instead more efficient routes are achieved because of the interaction between social learning and information pooling.

Pigeons (Columba livia) display reliable homing behaviour, but their homing routes from familiar release points are individually idiosyncratic and tightly recapitulated, suggesting that learning plays a role in route establishment. In light of the fact that routes are learned, and that both ascending and descending visual pathways share visual inputs from each eye asymmetrically to the brain hemispheres, we investigated how information from each eye contributes to route establishment, and how information input is shared between left and right neural systems. Using on-board global positioning system loggers, we tested 12 pigeons' route fidelity when switching from learning a route with one eye to homing with the other, and back, in an A-B-A design. Two groups of birds, trained first with the left or first with the right eye, formed new idiosyncratic routes after switching eyes, but those that flew first with the left eye formed these routes nearer to their original routes. This confirms that vision plays a major role in homing from familiar sites and exposes a behavioural consequence of neuroanatomical asymmetry whose ontogeny is better understood than its functional significance.

Many animals, and birds in particular, are thought to use directional information from the sun in the form of a time-compensated sun compass, with predictably deviated orientation under clock shift being regarded as the litmus test of this. We suggest that this paradigm obscures a number of other ways in which solar-derived information could be important in animal orientation. We distinguish between the known use of the sun's azimuth to provide absolute geographical direction (compass mechanism) and its possible use to detect changes in heading (heading indicator mechanism). Just as in an aircraft, these two kinds of information may be provided by separate mechanisms and used for different functions, for example for navigation versus steering. We also argue that although a solar compass must be time-referenced to account for the sun's apparent diurnal movement, this need not entail full time compensation. This is because animals might also use time-dependent solar information in an associatively acquired, and hence time-limited, way. Furthermore, we show that a solar heading indicator, when used on a sufficiently short timescale, need not require time compensation at all. Finally, we suggest that solar-derived cues, such as shadows, could also be involved in navigation in ways that depend explicitly upon position, and are therefore not strictly compass-related. This could include giving directionality to landmarks, or acting as time-dependent landmarks involved in place recognition. We conclude that clock shift experiments alone are neither necessary nor sufficient to identify the occurrence of all conceivable uses of solar information in animal orientation, so that a predictable response to clock shift should not be regarded as an acid test of the use of solar information in navigation., Highlights • Sun compasses may be fully or only partially time compensated. • Navigational uses of noncompass solar information are explored. • The sun may be used as a heading indicator without time compensation. • Solar time-dependent place and landmark recognition are explored. • Clock shift is an ambiguous test of sun compass orientation.

Homing pigeons (Columba livia) have been the central model of avian navigation research for many decades, but only more recently has research extended into understanding their mechanisms of orientation in the familiar area. The discovery (facilitated by GPS tracking) that pigeons gradually acquire with experience individually idiosyncratic routes home to which they remain faithful on repeated releases, even if displaced off-route, has helped uncover the fundamental role of familiar visual landmarks in the avian familiar area map. We evaluate the robustness and generality of the route-following phenomenon by examining extant studies in depth, including the single published counter-example, providing a detailed comparison of route efficiencies, flight corridor widths and fidelity. We combine this analysis with a review of inferences that can be drawn from other experimental approaches to understanding the nature of familiar area orientation in pigeons, including experiments on landmark recognition, and response to clock-shift, to build the first detailed picture of how bird orientation develops with experience of the familiar area. We articulate alternative hypotheses for how guidance might be controlled during route following, concluding that although much remains unknown, the details of route following strongly support a pilotage interpretation. Predictable patterns of efficiency increase, but limited to the local route, typical corridor widths of 100–200 m, high-fidelity pinch-points on route, attraction to landscape edges, and a robustness to clock-shift procedures, all demonstrate that birds can associatively acquire a map of their familiar area guided (at least partially) by direct visual control from memorised local landscape features.

When homing from familiar areas, homing pigeons are able to exploit previously acquired topographical information, but the mechanisms behind this ability are still poorly understood. One possibility is that they recall the familiar release site topographical features in association with the home direction (site-specific compass orientation strategy), another that the spatial relationships among landmarks guide their route home (piloting strategy), without relying on the compass mechanism. The two strategies can be put in conflict by releasing clock-shifted birds at familiar locations, in order to highlight which is preferred. We analysed GPS tracks of clock-shifted pigeons, with familiarity controlled at each of three different release sites, and we observed that pigeons can display individual preferences for one of the two orientation strategies and that some characteristic features of the release site have an important role in determining the level of landmark-based homeward orientation. © 2013 Springer-Verlag Berlin Heidelberg.

It seems reasonable to assume that pigeons use visual features in the landscape for orientation when they are homing over familiar terrain. Experimental evidence to prove or disprove this possibility is, however, difficult to obtain. Here, we link the problem with the observation that deflections of initial orientation caused by clock-shift are often smaller than predicted on a pure sun compass basis. We substantiate the hypothesis that consistently reduced deflections and increased angular scatter occur only when pigeons are released in familiar areas where a remembered pattern of landscape features can conflict with the position of the sun. Repeated releases of the same individuals under clock-shift, or elimination of non-visual navigational clues (odours), appear to strengthen the conflicting influence of familiar visual landmarks. Accelerated returns of birds allowed to preview the surrounding familiar scenery before release also support the conclusion that the visual environment is included in the homing system of pigeons. The landscape, however, not only helps home-finding, if it is familiar, but may also have a distracting influence that contributes to the great variability of initial orientation patterns.

In previous experiments suggesting that previewing visual landscapes speeds homing from familiar release sites, restricted access to olfactory cues may have artefactually encouraged homing pigeons,Columba liviato resort to visual landmark orientation. Since evidence for the role of visual landmarks in wide-ranging avian orientation is still equivocal, Braithwaite & Guilford’s (1991,Proc. R. Soc. Lond. Ser. B245, 183–186) ‘previewing’ experiments were replicated: birds were allowed or denied visual access to a familiar site prior to release, but allowed ample access to olfactory cues. In experiment 1, allowing birds to preview familiar sites for 5 min prior to release enhanced homing speeds by about 12%. In experiment 2, modified to reduce between-day effects on variation, previewing enhanced homing speeds by about 16%. These experiments support the conclusion that visual landmarks remote from sight of the loft are an important component of the familiar area map, although the nature of the landmarks and how they are encoded remain to be determined.

Summary Birds have remained the dominant model for studying the mechanisms of animal navigation for decades, with much of what has been discovered coming from laboratory studies or model systems. The miniaturisation of tracking technology in recent years now promises opportunities for studying navigation during migration itself (migratory navigation) on an unprecedented scale. Even if migration tracking studies are principally being designed for other purposes, we argue that attention to salient environmental variables during the design or analysis of a study may enable a host of navigational questions to be addressed, greatly enriching the field. We explore candidate variables in the form of a series of contrasts (e.g. land vs ocean or night vs day migration), which may vary naturally between migratory species, populations or even within the life span of a migrating individual. We discuss how these contrasts might help address questions of sensory mechanisms, spatiotemporal representational strategies and adaptive variation in navigational ability. We suggest that this comparative approach may help enrich our knowledge about the natural history of migratory navigation in birds.

Conspicuousness is an important feature of warning coloration. One hypothesis for its function is that it increases signal efficacy by facilitating avoidance learning. An alternative, based on the handicap hypothesis, suggests that the degree of conspicuousness holds information directly about the quality of the prey, and that predators associate and learn about the conspicuousness of the coloration, and not the actual colour pattern. We studied the relative importance of signal contrast and the colours of signals for predator attention during discrimination. We used young chicks, Gallus gallus domesticus , as predators and small blue or red paper cones on either matching or contrasting paper backgrounds as stimuli associated with palatable or unpalatable chick crumbs. In four treatment groups, birds could use either cone and/or background colour, cone colour only, background colour only or cone-to-background contrast as cues for discrimination. Only birds in the contrast treatment failed to learn their discrimination task. Birds that had a choice between cone and background colour as cues used the cone colour and they learned the task faster than did birds that had to use background colour as a cue. The results suggest that birds primarily attend to the colours of signals and disregard contrast in discrimination tasks; they thus fail to support a handicap function of conspicuous aposematic coloration. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Little is known about the navigational abilities of domestic fowl. The question of how chickens represent and orient in space becomes relevant when they are kept in non-cage systems. Since the sun is known to be the dominant spatial organiser in other diurnal bird species, we started our investigation of the chicken's spatial abilities by subjecting them to a food-searching task with the sun as the only consistent visual cue. In an additional experiment we tried to rule out the use of auditory cues in finding a food reward. Eight ISA Brown chicks were housed in outdoor pens. A separate test arena comprised an open-topped, opaque-sided wooden octagon (2 m wide and 1.5 m high). Eight goal boxes with food pots were attached to each of the arena sides; a wooden barrier inside each goal box prevented the birds from seeing the food pot before entering. After habituation we tested during five daily 5 min trials whether the chicks were able to find food in a systematically allocated goal direction. Food residue in every foot pot controlled for the use of olfactory cues and no external landmark cues were visible. Every day each box was unpredictably moved to a randomly assigned side of the arena and the side to face north was also randomly allocated, to prevent the chicks from using cues other than the sun's position. Circular statistics were used to determine whether birds moved in a non-random direction and if so, if they significantly oriented goalwards. The results showed that seven of the eight birds moved significantly in the goal direction. It seems likely that the chicks used the sun to orient. Due to weather constraints only four chicks received the same treatment on a new location, to rule out the use of auditory cues. Two of these four chicks significantly moved in the goal direction. The results from our experiments show that domestic chicks use spatial memory to orient towards a hidden goal. Moreover, their orientation is most likely to be based on sun cues opening up the possibility that the sun compass may dominate even in this ancestrally predominantly ground-living forest bird. © 2002 Elsevier Science B.V. All rights reserved.

The recognition of familiar areas by homing pigeons, Columba livia, is now known to depend at least in part on visual cues. Birds allowed a 5-min preview of the surrounding landscape prior to release home faster than those denied access to such cues, suggesting that recognition is visually mediated. We examined this phenomenon further by asking how memory generated through prior experience with a site is used in recognition. We provided a group of homing pigeons with training experience in which they viewed, through a single transparent vertical face of an otherwise opaque release box, an approximately 140° segment of the landscape for 5 min before release. Training previews were always given from consistent locations and orientations within a release site. Test releases that followed were used to ascertain whether subsequent site recognition necessitated previewing from this already familiar angle and distance, or whether the skill could be extended to novel, nonoverlapping lateral views of the landscape. The results suggested that homing performance was better after presentation of the view recapitulating that seen during training than after showing a novel alternative view. Pigeons may have been using a template of the arrangement of familiar landmarks around the release site as the cue for recognition. The effect, however, disappeared after repeated training, suggesting that repeated release from a site may allow for more extensive visual survey and the memorization of detailed features of the landscape or the extraction of site-specific general features that aid recognition even when a novel view is presented. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Unpalatable insects frequently adopt multimodal signals to ward off predators, incorporating sounds and odours into their colourful displays. Pyrazine is an odour commonly used in insect warning displays, and has previously been shown to elicit unlearned biases against common warning colours, e.g. yellow and red in naive predators. We designed two experiments to test for similar effects of pyrazine on the conspicuousness of prey, perhaps the most ubiquitous aspect of aposematic coloration. In the first experiment, we offered predators ( Gallus gallus domesticus ) a choice between conspicuous crumbs and cryptic crumbs in the presence or absence of pyrazine. In the second experiment, we manipulated the birds' experience of conspicuous prey during an initial training phase. Only in the presence of pyrazine did birds show a bias against conspicuously coloured food, and this occurred whether or not they had previously experienced food that contrasted with the background. This emergent behaviour relied upon the visual and odorous signal components being presented together. These unlearned, yet hidden, responses against conspicuousness demonstrate that there are initial benefits to prey being conspicuous when the multimodal nature of warning signals is accounted for.

We describe an experiment that uses the grouping tendencies and navigational abilities of the homing pigeon (Columba livia) to investigate the possibility of socially mediated information transfer in a field setting. By varying the composition of paired-release types, we allowed some naive birds to receive an accurate demonstration of the home route whilst others were paired with similarly naive conspecifics. After this 'paired phase', we predicted that if any learning of spatial information occurred then naive members of the former pairs would outperform their untutored conspecifics when re-released individually during the subsequent 'single phase' of the experiment. This prediction was not confirmed. Neither homing speed nor initial orientation was superior in individually released tutored versus untutored birds, despite the fact that both performance measures were better in the earlier 'paired phase' with experienced demonstrators. Our results suggest that although naive homing pigeons clearly interact with their experienced partners, they are unable to transfer any individually useful spatial information to subsequent homing flights.

We adapted a technique to explore the social transmission of spatial information in homing pigeons Columba livia. Five demonstrator pigeons were first trained to find a food goal within an indoor arena. This arena consisted of nine lidded cups laid out within a 12x12 grid on the floor. The task was to find the goal cup and flip the lid to obtain the food hidden within. Once the demonstrators had reached criterion the experiment proper began. During stage 1 of the experiment, 10 target birds, which had not previously been trained to find the goal, were introduced to the spatial task either in isolation or paired with a demonstrator. We measured how long they took to complete the task, the number of squares crossed on the grid, and the number of incorrect lids flipped. In stage 2, the target birds were introduced to the arena a second time, by themselves, and we compared the performance of the birds in the two treatments. The pigeons that had been introduced to the task with a demonstrator in stage 1 walked further and made more incorrect choices when searching for the food goal in stage 2 than the pigeons that were introduced to the task alone. This indicates that pigeons learn a spatial, food-finding task more effectively when performing the task alone than when accompanied by a knowledgeable conspecific. We discuss possible reasons for this in the light of previous experiments. Copyright 1999 The Association for the Study of Animal Behaviour.

Two experiments are described which investigate the orientational consequences of flocking in homing pigeons Columba livia. Previous experiments have shown that homing pigeons placed inside a clear-sided release box for 5 min before release from a familiar site have enhanced ground homing speed compared with those placed in an opaque-sided box. It is assumed that previewing the surrounding landscape allows for faster homing since a bird denied this information must accumulate the knowledge on release. In experiment 1, using the same technique developed in these experiments but releasing the birds in pairs we showed that within familiar areas, homing pigeons can exploit a partner that has acquired more information, allowing them to home more quickly. In experiment 2 we attempted to test three potential strategies which may occur during homing flights. The results do not conclusively distinguish between these three mechanisms but suggest that orientation of the pairs of birds is most likely to have resulted from a compromise of individual tendencies, or from following the best homer, but not from following a 'governing leader'. The consequence of these mechanisms is discussed.

A potentially valuable method for investigating the role of visual landmarks in the familiar area map is to use an open-field arena food-searching task, allowing landmarks and the sun compass to be independently manipulated. In previous such experiments performed outdoors, homing pigeons, Columba livia, primarily used the sun compass rather than visual cues to locate the target goal. One possible reason for this result may have been that the artificial two-dimensional landmarks provided lacked salience, forcing the pigeons to rely on the sun compass. In this study the salience of two-dimensional visual cues indoors, where the sun compass was not available, was investigated. As pigeons were unexpectedly unable to learn this task consistently, in a second experiment a three-dimensional cue was added. The results suggest that: (1) pigeons are unable to use two-dimensional cues to locate the target goal consistently, when no other directional cues are available, but are able to use a three-dimensional cue in an otherwise identical task; (2) pigeons do not use non-visual cues (such as the magnetic compass) indoors to locate the target goal; and (3) the scatter in mean bearings often observed in clock-shifted pigeons is not caused by non-specific disturbance resulting from shifting the internal clock. The significance of our results is discussed in relation to the homing mechanisms used by pigeons at familiar sites.

Animal signals that are conspicuous or extravagant are commonly explained as costly advertisements of ‘quality.’ There are, however, many other evolutionary explanations of conspicuousness, most notably those to do with ‘efficacy’ or factors making signals effective at getting their message across to receivers. Efficacy can be a major evolutionary force driving signals toward conspicuousness even if there is no selection pressure to advertise quality. Its effects have been widely underestimated through a failure to understand the variety of different ways in which it can act. Efficacy offers a variety of alternative explanations for the evolution of signals, including extravagant sexual signals and can also explain a further feature of animal signals, namely the diversity between species in the signals they use.

ANIMAL signals are often 'multicomponent'1–3, consisting of displays with several parts to allow exploitation of different senses. An example is the courtship display of the peacock, which combines dashing movements with a noisy, shimmering show of his train feathers4. Yet the significance of multicomponent signalling is unknown. As a model multicomponent signalling system, we investigated the warning signals of toxic insects, which often combine pyrazine odours with conspicuous coloration such as yellow or red5–7. Here we demonstrate, in prey choice experiments with birds, that pyrazine interacts with red and yellow to induce strong aversions to these aposematic colours that are not shown in the absence of the odour. Pyrazine is shown neither to be inherently aversive, nor to induce aversion to a non-aposematic colour, green. To our knowledge, this study provides the first evidence that the function of multicomponent signals can lie in hidden psychological responses produced by the interaction of their components.

Using the flocking tendencies of homing pigeons ( Columba livia ) in flight, a first attempt was made to test directly the hypothesis that group movement may have a navigational function. We manipulated the potential advantage of transfer of navigational information by releasing pairs of homing pigeons in which none, one or both of the birds had previously been released at sites about 25 km from the home loft (while overall flying experience was standardized). Contrary to our prediction, locally naive birds did not follow experienced birds home, whereas experienced birds, with less navigational need to flock, were generally still paired on arrival home. Pairs in which both birds were locally naive also tended not to home together. Under the conditions of our experiment, the tendency to fly together appeared not to have a navigational function. However, and contrary to recent conclusions in the literature, our results do suggest that the initial flight behaviour of birds at novel release sites may constitute a navigational information gathering strategy that is sufficiently important to over-ride gregarious tendencies when the two conflict.

Confusion over the validity of ‘conventional signalling’ may have resulted at least in part because it has been used to refer to different concepts. The main aim of this paper is to expose the source of this confusion, not to prescribe a particular solution. Two key current senses of conventional signals are identified: (1) as strategic correlates of quality (or, more generally, of the parameter about which information is contained in the signal's message); (2) as signals whose design is arbitrarily related to their message. The sometimes difficult relationships between these two senses and other concepts in the signalling literature (assessment signals, strategic choice handicaps, direct indicators, revealing handicaps) are explored. It is concluded that two separate but important distinctions have been used to characterize conventional signals (first, whether or not signals allow strategic choice, and, second, whether signalling costs are intrinsic to the signal's production), and that these remain of significance to the understanding of signal design. The paper concentrates mainly on signalling between parties with conflicting evolutionary interests, but briefly shows how these concepts may relate to signalling systems with no conflict of interest.

Although much is now known about the navigational strategies of homing pigeons, Columba livia, much less is understood about the nature of their familiar area map. Although familiar visual landmarks are probably important, it is not yet known whether birds can pilot using the arrangement of landmarks directly, or whether landmarks merely specify sun compass directions home. In this study we develop a laboratory `analogue' of the familiar area orientation problem, and show that pigeons primarily use sun compass information to encode the direction of a food goal, despite the presence of prominent, fixed, directional visual cues, and under both visual cue-shift and clock-shift conditions. Our results suggest that the sun compass is deeply embedded in the way pigeons represent their spatial environment.

Automimicry is the existence of palatable individuals in an unpalatable, warningly coloured (i.e. aposematic) prey species. Because automimics are visually indistinguishable from their models, they present a special problem for the evolutionary stability of aposematism. Traditionally this problem has remained either unrecognized, or has been considered solved by the actions of naive predators that attack warningly coloured prey, eating them if palatable, rejecting them if unpalatable. Although naive predators can stabilize aposematism against invasion by automimics, the conditions under which they can do so are restricted. It is argued here that an adjustment to the traditional view of how aposematic signals operate can offer a more general solution to the problem of automimicry. The "go-slow signalling" solution proposes that some predators learn not to avoid aposematic prey, but to sample them cautiously in order to determine their true palatability more accurately. Because unpalatable prey can benefit by advertising conspicuously to go-slow predators, but cannot benefit by advertising to naive predators (unless predators are innately cautious of conspicuously coloured prey), go-slow signalling can stabilize aposematism under a wider range of conditions than can traditional naive predators. The assumptions, predictions, and empirical implications of the go-slow signalling hypothesis are discussed.