Opponent Assessment Research Articles

MEANS OF SPEECH AGRESSIVENESS IN AN ELECTION CAMPAIGN

The article discusses means of expressing aggressiveness used in the newspaper “LDPR in Udmurtia” during election campaigns. Despite a large number of implicit means that politicians and journalists are equipped with, the newspaper demonstrates explicit means of speech aggressiveness. The style of the publications is a replica of speech manner of the LDPR leader. One of the major ways of expressing negative assessment of political opponents is conversational and colloquial vocabulary of deflated style. The authors of this media tend to use phraseology with non-normative connotation. Expressive means used by journalists tend to sound negative and aim to discredit the existing power. To demonstrate negative attitude to the government a variety of stylistic means are used including repetitions, gradation, rhetoric questions, rhetoric exclamations and addressing. In the newspaper of the opposition party ethical and linguistic norms are broken, negative information disclosing situation in the country tend to form readers’ sense of frustration.

Use of Selected Geospatial Tools for the Purposes of Reconnaissance

The implementation of modern tools in the military system constitutes an important step in supporting the decision-making process. The impact of new GIS technologies is important for the assessment of the battlefield . According to assumptions, reconnaissance is a continuous process that crowns the assessment of the opponent and of the battlefield. Site assessment is an element of the command process where the conclusions of the task analysis includes an assessment of the potential opponent together with his modus operandi and an assessment of the environment . As part of the Information Preparation of the Battlefield (hereinafter referred to as IPB), the identification of threats and limitations has an impact on the identification of potential approach routes, traffic corridors and maneuvers in assigned areas and lanes . The end result is the determination of the maneuverability of forces and resources owned or those of the opponent. The information is to relate to the impact of the terrain components on the scope and nature of conducted activities, and the hydrometeorological conditions are to relate to the impact on the terrain, equipment, and people . As far as it regards the analysis of the environment and the opponent, it is possible to apply modern technologies to shorten the time for the analyses performed within the ongoing decision-making process.

Advantages of social skills for contest resolution.

Animal contests are natural interactions that occur to obtain or defend resources such as food and territory. Selection should favour individuals that can win contests with minimal costs in terms of energy expenditure or injuries. We hypothesized that social skills contribute to animals' assessment abilities in a contest situation and thereby will shorten contest duration. Animals were either raised in early life conditions stimulating the development of social skills, termed socialization or not (control). Contests between 342 pigs at eight weeks old (171 dyads) were studied for opponent assessment ability (using a game theoretical approach), examining duration and escalation, social behaviours performed, injuries and outcome. Contesting dyads were from the same treatment group and varied in body weight, a validated measure of resource holding potential (RHP). Socialized animals had shorter contests that were resolved with fewer injuries and they showed more ritualized display behaviour, consistent with mutual assessment. Furthermore, there was evidence of a novel form of opponent assessment in the socialized group revealed by a positive relationship between winner RHP and fight duration. In conclusion, social skills enabled more rapid establishment of dominance relationships at lower cost. Besides its evolutionary relevance, these findings may also contribute towards improving animal welfare.

American lobsters, Homarus americanus, use vision for initial opponent evaluation and subsequent memory

Many animals, including crustaceans, engage in dominance fights and thus the risk of damage. This makes opponent assessment a critical component of social information gathering. American lobsters, Homarus americanus (H. Milne-Edwards, 1837), are well known for surprisingly complex social behavior. Males fight for dominance, and winners are preferred by females. Fighting success is correlated with body and claw size. To avoid injury, opponents assess each other before and during a fight. The loser later recognizes the winner based on urine odor and retreats early from subsequent fights. Most research has explored recognition in the context of chemical ecology. Here, we describe four experiments testing the largely unexplored visual communication of male lobsters. Two experiments address evaluation within unfamiliar pairs. The first shows that the visual image of a lobster's own reflection in a mirror enhances attacks on an unfamiliar conspecific odor plume. The second shows that increasing differences in crusher claw size between opponents cause gradually decreasing fight duration; this negative correlation is maintained when either vision or olfaction is blocked. Blocking either sense caused similar increases in fight duration. Two additional experiments tested visual memory of opponents. Blindfolding the loser of a first fight abolished the decrease in second-fight duration seen in control fights, similar to previous results based on blocking olfaction. Finally, painting the face (carapace around the eyes and rostrum) of the winner in a second fight did not prevent recognition by the loser. Together, these results demonstrate that vision makes contributions to lobster communication, specifically opponent evaluation.

Computer animations of color markings reveal the function of visual threat signals in Neolamprologus pulcher.

Visual signals, including changes in coloration and color patterns, are frequently used by animals to convey information. During contests, body coloration and its changes can be used to assess an opponent’s state or motivation. Communication of aggressive propensity is particularly important in group‐living animals with a stable dominance hierarchy, as the outcome of aggressive interactions determines the social rank of group members. Neolamprologus pulcher is a cooperatively breeding cichlid showing frequent within-group aggression. Both sexes exhibit two vertical black stripes on the operculum that vary naturally in shape and darkness. During frontal threat displays these patterns are actively exposed to the opponent, suggesting a signaling function. To investigate the role of operculum stripes during contests we manipulated their darkness in computer animated pictures of the fish. We recorded the responses in behavior and stripe darkness of test subjects to which these animated pictures were presented. Individuals with initially darker stripes were more aggressive against the animations and showed more operculum threat displays. Operculum stripes of test subjects became darker after exposure to an animation exhibiting a pale operculum than after exposure to a dark operculum animation, highlighting the role of the darkness of this color pattern in opponent assessment. We conclude that (i) the black stripes on the operculum of N. pulcher are a reliable signal of aggression and dominance, (ii) these markings play an important role in opponent assessment, and (iii) 2D computer animations are well suited to elicit biologically meaningful short-term aggressive responses in this widely used model system of social evolution.

Video playback experiments support a role for visual assessment of opponent size in male-male contests of Servaea incana jumping spiders

Jumping spiders (Salticidae) are known both for their excellent vision and for the elaborate visual displays they use to mediate intraspecific interactions. Despite appearing well adapted for visual exchange of information, several correlative studies have suggested that jumping spiders, including Servaea incana, may not visually assess opponent size during agonistic interactions. To more directly examine whether jumping spiders are able to visually assess opponent size, we examined how males of S. incana respond to videos of agonistic displays from various sized conspecifics. Videos of small and large spiders were manipulated so that each opponent exemplar was presented at four sizes that spanned the range of natural variation. Tendency of live spiders to display at and approach videos were related to both their own size and the final size of the video opponents, but not the original size of the video opponents. Small spiders were less likely to display towards large opponents than small opponents whereas large spiders were more likely to display towards large opponents than small opponents. S. incana jumping spiders appear to possess the sensory ability to visually assess opponent size, but their slow visual system and the dynamic behaviour of the opponents during contests may reduce opportunities for visual assessment to the point where individual size-associated tendencies come to dominate decisions of persistence, escalation and retreat. To limit the costs of fighting, animals may assess their opponent’s fighting ability to decide when to withdraw from contests. Alternatively, animals may withdraw from contests when they reach a cost threshold, regardless of the ability of their opponent. Studies with live interactions suggest that jumping spiders rely on the latter strategy, despite their use of ritualised displays and excellent vision. Using video playback techniques, we demonstrate that Servaea incana males are able to visually assess their opponents during contests. The probability of displaying towards and approaching a video opponent depended upon both a spider’s own size and the size of the video opponent. However, an interaction between these factors suggests that there may be limited opportunity for assessment in live interactions and that the costs and benefits of opponent assessment may depend on an animal’s own fighting ability.

The mechanosensory lateral line is used to assess opponents and mediate aggressive behaviors during territorial interactions in an African cichlid fish

Fish must integrate information from multiple sensory systems to mediate adaptive behaviors. Visual, acoustic and chemosensory cues provide contextual information during social interactions, but the role of mechanosensory signals detected by the lateral line system during aggressive behaviors is unknown. The aim of this study was first to characterize the lateral line system of the African cichlid fish Astatotilapia burtoni and second to determine the role of mechanoreception during agonistic interactions. The A. burtoni lateral line system is similar to that of many other cichlid fishes, containing lines of superficial neuromasts on the head, trunk and caudal fin, and narrow canals. Astatotilapia burtoni males defend their territories from other males using aggressive behaviors that we classified as non-contact or contact. By chemically and physically ablating the lateral line system prior to forced territorial interactions, we showed that the lateral line system is necessary for mutual assessment of opponents and the use of non-contact fight behaviors. Our data suggest that the lateral line system facilitates the use of non-contact assessment and fight behaviors as a protective mechanism against physical damage. In addition to a role in prey detection, the diversity of lateral line morphology in cichlids may have also enabled the expansion of their social behavioral repertoire. To our knowledge, this is the first study to implicate the lateral line system as a mode of social communication necessary for assessment during agonistic interactions.

Fighting cichlids size up opposition with lateral line

When sizing each other up before a confrontation, most males depend on all of their senses to learn more about their opponent – listening, watching and sniffing out strengths and weaknesses. However, Karen Maruska and Julie Butler, from Louisiana State University, USA, explain that fish also explore their surroundings with an additional sense: the lateral line system responds to the ebb and flow of water surrounding the fish's body. Could fish also use this ‘touch at a distance’ system to learn more about a foe? Maruska and Butler explain that fish adversaries often waft water around while posturing in preparation for an encounter and add, ‘The lateral line is poised to provide crucial information for opponent assessment’. However, no one had ever tested whether fish resort to the specialised sense in preparation for combat. ‘Astatotilapia burtoni males use a variety of aggressive behaviors, such as lateral displays, border fights, biting and mouth fights to defend their spawning territory,’ says Butler, so the scientists selected this aggressive species to test their theory.First, the duo investigated the structure of the feisty males’ lateral line system and clearly saw the sensory units that detect disturbances in water distributed on the fish's head and along the side of the body. Then they selected dominant males that were keen to defend their territory and deactivated the animals’ lateral line systems by immersing them in a solution of cobalt chloride and severing the posterior lateral line nerve. Next, they paired combinations of males, with and without active lateral line systems, in a duel over new territory and filmed the encounters.Butler explains that for each contest there were three possible outcomes: the fish did not fight; one fish capitulated to the other before full hostilities began; or the fish battled for supremacy. Analysing the outcomes of each confrontation, the duo quickly saw that the lateral line system was an essential component of a successful non-confrontational outcome.Almost 75% of the pairs where both fish had an intact lateral line system battled. However, when a dueller with a lateral line system was pitched against an opponent that had lost the sense, the duo saw a large increase in the proportion of fish that backed down before a confrontation – up from 5% in two males with intact lateral line systems to 30% where one combatant had lost the use of the lateral line. ‘This decreased motivation was likely due to an impaired ability to adequately assess the opponent’, say Butler and Maruska, adding that the disabled fish spent more time in close proximity to their opponents than the intact fish and that fish that had lost the lateral line system failed to instigate combat with the fin-flaring display that intact fish perform before a skirmish. And when Butler and Maruska analysed the battle manoeuvres, they saw that the fish with a functional lateral line system avoided contact with their opponents, while the fish that had lost the system bit and rammed each other more.Butler and Maruska were impressed to find that the fish use the additional sense to avoid damaging confrontation and they say, ‘To our knowledge, this is the first study to implicate the lateral line system as a mode of social communication necessary for assessment during agonistic interactions’.

David vs. Goliath: Serotonin modulates opponent perception between smaller and larger rivals

During agonistic encounters, the perception of a larger opponent through morphological signaling typically suppresses aggression in the smaller individual, preventing contest intensity escalation. However, non-morphological factors such as central serotonin (5-HT) activity can influence individual aggression, potentially altering contest intensity despite initial size discrepancies. When male stalk-eyed flies (Teleopsis dalmanni) fight, contest escalation is directly proportional to similarity in body size, with escalation being lower in size-mismatched contests. We have shown that both high-intensity aggression and the probability of winning are increased in males with pharmacologically elevated 5-HT relative to size-matched non-treated opponents. Here, we hypothesized that, in size-mismatched contests, increasing brain 5-HT in the smaller opponent could similarly increase aggression and counteract the low contest intensity normally driven by size discrepancy. Size-mismatched male pairs (greater than 5% difference in eyestalk length) engaged in a forced fight paradigm, with the smaller fly either untreated or with pharmacologically elevated 5-HT levels. The expression of high-intensity aggressive behaviors was significantly increased in smaller treated opponents, but the probability of winning was not altered. This suggests that while elevated serotonergic activity can increase aggression and intensity despite perception of a larger opponent, this is not sufficient to overcome size biases with respect to contest outcome. However, the fact that larger opponents continued to win against smaller treated flies was not simply a function of size. Instead, untreated larger males adjusted their fighting strategy to match the increased aggression of their smaller treated opponent, suggesting contextual flexibility in behavior based on individual opponent assessment.

Egg-spot pattern and body size asymmetries influence male aggression in haplochromine cichlid fishes

Assessing an opponent’s strength is an important component of attack strategies in territorial combats between males. Body size is often considered to directly influence an individual’s strength, but other honest visual signals may also affect the assessment of opponents. Among such visual signals are the so-called egg-spots, a conspicuous ovoid marking on the anal fin of male haplochromine cichlid fishes, made up of carotenoid-containing and other pigment cells. It has long been assumed that egg-spots are mainly relevant in courtship and spawning behavior, and previous work has focused primarily on their function in intersexual selection. Recently, however, both body size and egg-spots have been suggested to play a role in male–male interactions. To test whether egg-spots function in female choice or whether egg-spots and/or body size function as a predictor of strength and the subsequent attack strategy in male–male interactions, we performed a series of behavioral experiments in the haplochromine cichlid Astatotilapia calliptera. The trials revealed a limited involvement of egg-spots in female choice, yet a much stronger influence in male interactions. Territorial males combined information from the strength assessment based on body size and egg-spots to adopt their attack strategies. They launched more attacks against the larger intruder with many egg-spots compared with the smaller intruder without or with fewer egg-spots. Our study provides evidence that egg-spots serve as honest visual signal and that the level of asymmetries in egg-spot pattern and body size determines the relative impact of each trait in strength assessment.

Using visual modelling to study the evolution of lizard coloration: sexual selection drives the evolution of sexual dichromatism in lacertids

Sexual selection has been invoked as a major force in the evolution of secondary sexual traits, including sexually dimorphic colourations. For example, previous studies have shown that display complexity and elaborate ornamentation in lizards are associated with variables that reflect the intensity of intrasexual selection. However, these studies have relied on techniques of colour analysis based on human--rather than lizard--visual perception. Here, we use reflectance spectrophotometry and visual modelling to quantify sexual dichromatism considering the overall colour patterns of lacertids, a lizard clade in which visual signalling has traditionally been underrated. These objective methods of colour analysis reveal a large, previously unreported, degree of sexual dichromatism in lacertids. Using a comparative phylogenetic approach, we further demonstrate that sexual dichromatism is positively associated with body size dimorphism (an index of intrasexual selection), suggesting that conspicuous coloration in male lacertids has evolved to improve opponent assessment under conditions of intense male-male competition. Our findings provide the first evidence for the covariation of sexual dichromatism and sexual size dimorphism in lacertids and suggest that the prevalent role of intrasexual selection in the evolution of ornamental coloration is not restricted to the iguanian lineage, but rather may be a general trend common to many diurnal lizards.

Surprise, Deception, Denial and Warning: Strategic Imperatives

This article frames the highly complex national security challenges of surprise, denial and deception. These ultimate asymmetric threats exploit vulnerabilities, capitalizing on hubris, complacency and self-delusion. Such actions prevent the full and accurate assessment of opponents’ capabilities and intentions, and hinder appropriate actions. The long and frequent history of surprise, denial and deception suggest that these are essentially psychological phenomena. They are effective because they challenge and exploit perceptions that fill the gap between what is known and unknown. The authors present decision superiority as the fusion of information dominance and decisive action. Technology and intelligence can enhance decision superiority by ameliorating, but not eliminating, the limits of human perception. Translating knowledge into capabilities and actions requires agile, adaptive processes and open institutional collaboration within the interagency, with global allies and the private sector.

Factors leading to the evolution and maintenance of a male ornament in territorial species

Male ornamentation is assumed to have evolved primarily from selection by female mate choice. Yet this is only one possible reason for ornament evolution. Orna- ments might also be useful in aggressive competition by improving opponent assessment between males, or they might function to enhance signal detection by making males more conspicuous in the environment. We tested both these ideas in territorial Anolis lizards in which female choice is either absent or secondary to males competing for territories that overlap female home ranges. Male tail crests only evolved in species in which territory neighbors were distant, consistent with the signal detection hypothesis. Once the tail crest had evolved, however, it seems to have become a signal in itself, with variation in the frequency and size of tail crests within species correlating with variables predicted by the aggressive competition hypoth- esis. Our study presents an apparent example of a male ornament in which the selection pressure leading to variation among species in ornament expression is different from the selection pressure acting on variation within species. The Anolis tail crest is therefore likely to be an exaptation. We caution that conclusions made on the evolution of male ornaments are dependent on the phylogenetic perspective adopted by a study. Studies restricted to single species are useful for identifying selection pressures in contemporary settings (i.e., the current utility of traits), but may lead to erroneous conclusions on the factors that initially lead to the origin of traits.

Free-ranging dogs assess the quantity of opponents in intergroup conflicts

In conflicts between social groups, the decision of competitors whether to attack/retreat should be based on the assessment of the quantity of individuals in their own and the opposing group. Experimental studies on numerical cognition in animals suggest that they may represent both large and small numbers as noisy mental magnitudes subject to scalar variability, and small numbers (≤4) also as discrete object-files. Consequently, discriminating between large quantities, but not between smaller ones, should become easier as the asymmetry between quantities increases. Here, we tested these hypotheses by recording naturally occurring conflicts in a population of free-ranging dogs, Canis lupus familiaris, living in a suburban environment. The overall probability of at least one pack member approaching opponents aggressively increased with a decreasing ratio of the number of rivals to that of companions. Moreover, the probability that more than half of the pack members withdrew from a conflict increased when this ratio increased. The skill of dogs in correctly assessing relative group size appeared to improve with increasing the asymmetry in size when at least one pack comprised more than four individuals, and appeared affected to a lesser extent by group size asymmetries when dogs had to compare only small numbers. These results provide the first indications that a representation of quantity based on noisy mental magnitudes may be involved in the assessment of opponents in intergroup conflicts and leave open the possibility that an additional, more precise mechanism may operate with small numbers.

Assessment of self, opponent and resource during male–male contests in the sierra dome spider, Neriene litigiosa: Linyphiidae

Contestants in agonistic encounters may use assessments of self, opponent and resource quality as a basis for making behavioural decisions. Ritualized displays reduce risk and energy expenditure during assessments, but may lead to injurious fighting behaviour under certain circumstances. In this study, we examined the decision-making process of male sierra dome spiders (Neriene (¼Linyphia) litigiosa: Linyphiidae) during 323 maleemale contests using multivariate analysis. In contests over females, male ritualized displays include distinct phases by which males facultatively escalate fights: ritualized noncontact display, pedipalp wrestling, and unritualized biting and grappling. Amongst these phases we found evidence for all three types of assessment. Self-assessment was indicated by effects of the lighter male’s mass and the metabolic effect of temperature. These factors influenced the duration of noncontact display, likelihood of escalation and energetic expenditures. Opponent assessment, indicated by the effects of the difference in mass between contestants, influenced all aspects of fight behaviour when differences in body mass were large. When differences in body mass were small, relative mass only affected the duration of the fight, primarily by lengthening noncontact display. Resource assessment, measured through effects of female reproductive value and the males’ future reproductive opportunities, primarily influenced the decision to escalate to unritualized combat and the duration of the unritualized combat. Our multivariate analysis of behaviourally distinct phases of contests showed that contestants use diverse information to adjust investment in displays and potentially injurious fighting. We discuss the roles of information transfer versus raw attempts to influence outcomes in this complex contest system.

Signal residuals and hermit crab displays: flaunt it if you have it!

In animal contests selection should favour information gathering regarding the likely costs and benefits of continued conflict, and displays may provide a means for contestants to gain information about the fighting ability or aggressive intent of competitors. However, there is debate over the reliability of such displays and low levels of deception may occur within otherwise honest signalling systems. Hermit crabs use displays involving the chelipeds during agonistic encounters. We examined how variation in chelae size in relation to body size, a determinant of fighting ability, affects their use in displays and the process and outcome of contests over gastropod shells. In accordance with deceptive use of an otherwise honest signal, we found that contestants with large chelipeds for their body size spent more time performing the cheliped presentation display. Moreover, cheliped residuals and displays influenced the escalation level of encounters. There was a positive association between cheliped displays and the occurrence of ‘grappling’, but a negative association between displays and the occurrence of shell fights, suggesting that displays may signal aggressive intent and a reluctance to back off or accept the more passive defender role in a fight. Furthermore, the smaller of the two contestants in shell fights had larger cheliped residuals compared to those smaller contestants not involved in shell fights, which is consistent with disrupted opponent assessment. This study adds to mounting evidence that when acting as a signaller, individuals for whom the display exaggerates competitive ability attempt to manipulate opponents, using the display more often.

Opponent assessment in lizards: examining the effect of aggressive and submissive signals

During conflict, males often assess their opponent’s fighting ability and motivation via dynamic signals. We conducted an interactive video playback study using male Jacky dragons, Amphibolurus muricatus, to determine which signalling strategy was the most effective at deterring aggression and eliciting submission. A 3D computer-animated lizard was used to present aggressive signals (push-up displays) and submissive ones (slow arm-waves). This approach reproduced natural display motor patterns precisely while controlling variation in morphology. Treatments all commenced with the stimulus lizard producing bouts of push-ups, but then diverged after the subject lizard’s responses, according to predetermined rules. Lizards attacked the stimulus more frequently when it responded to submission with slow arm-waves, revealing that their behavior during a contest is sensitive to social contingencies. Individuals that signal submission without retreating are likely to incur a receiver retaliation cost. In addition, assessment processes are surprisingly sophisticated, involving the monitoring of both an index signal (push-ups) and a conventional one (slow arm-waves) during a single interaction. Key words: Amphibolurus, interactive playback, signalling, submissive display, threat display. [Behav Ecol]

Lethal male–male combat in the parasitoid Melittobia acasta: are size and competitive environment important?

Interactions between organisms can lie anywhere along the spectrum from fatal conflict to total cooperation. To understand this variation, knowledge of the strategies that individuals use to acquire their resources is required. We tested theoretical predictions relating to conflict behaviour in a species of parasitoid wasp, Melittobia acasta, in which males compete for mates in their closed, natal patches. They engage in lethal combat to gain access to the females developing in their host. Environmental factors and individual traits both influenced conflict behaviour and contest outcome: fighting behaviour increased with the density of competitors and larger contestants were more successful. Our results also indicate that opponent assessment did not influence conflict behaviour and contests were always resolved by fighting.

Assessment of repeated displays: a test of possible mechanisms

Many animals signal their resource holding potential (RHP) to deter competitors from engaging them in potentially costly fights. Studies of this opponent assessment function have generated important insights into signal design and evolution. In the case of sounds, rate of production is often a salient feature. We used digital video playback to conduct analogous experiments exploring the importance of temporal variation in visual signals. Our study focused on the push-up display of male Jacky dragons Amphibolurus muricatus, an Australian agamid lizard. This stereotyped movement-based signal is commonly performed during male-male contests. A previous study has shown that Jacky dragons responses are influenced by the overall display rate of a video conspecific. We built upon this finding by investigating the effect of short-term variation in display rate. Each playback sequence varied systematically across a different combination of display parameters, while keeping the total number of push-ups constant. Other potential cues, such as morphology and the characteristics of individual motor patterns, were precisely controlled. The aggressive signalling and locomotor behaviour of subject males varied significantly between sequences. Most notably, performance of throat expansions, a typical agamid threat posture, was suppressed by video sequences with temporal clumping of displays. These results show that lizards are sensitive to differences in the temporal fine structure of display sequences and suggest that display concentration is an important assessment cue.

AGONISTIC INTERACTIONS IN A LIOLAEMUS LIZARD: STRUCTURE OF HEAD BOB DISPLAYS

Males from different iguanian lizard species engage in frequent visual signaling during agonistic interactions, mainly by displaying head bobs. We conducted a detailed study of the structure of head bob displays mediating male agonistic interactions in Liolaemus lemniscatus lizards. We staged pair-wise encounters where one male, the intruder, was placed in the terrarium of a conspecific male, the resident. During these interactions, males exhibited only one type of head bob display made up of three distinct units: a low amplitude bob (unit 1), a brief pause (unit 2), and two consecutive high-amplitude bobs (unit 3). Head bob displays occurred singly or as a part of a bout, with a mean number of head bob displays per bout of two. Total head bob display duration was stereotyped. The highest inter-individual variation (duration and amplitude) was recorded for unit 3, suggesting that this unit may provide information about the individual identity of the sender. Winners of interactions performed more head bob displays than losers, and these were composed of units of longer duration and higher amplitude than head bob displays exhibited by losers. Although preliminary, our results suggest that, in L. lemniscatus, head bob displays may facilitate opponent assessment by conveying information about individual fighting ability, motivation, or dominance status.