Intensity Of Aggression Research Articles

Effects of nozzle inner surface roughness on the cavitation erosion characteristics of high speed submerged jets

Cavitating jet is now being widely used in a variety of situations due to its strong aggressive erosion ability. In order to push the erosion capability to a maximum, the effects of nozzle inner surface roughness on the cavitation erosion characteristics of submerged cavitating jets were experimentally investigated for the first time with respect to aggressive erosion intensity and efficiency. By impinging the submerged jets on specimens of pure aluminum (1070A) using six organ-pipe cavitating nozzles of different surface roughness values (0.8μm , 1.6μm, 3.2μm, 6.3μm, 12.5μm, and 25μm), the mass loss and specific energy consumption at various inlet pressures and standoff distances were measured and analyzed. And the macroscopic appearances of eroded specimens at optimum standoff distances corresponding to each inlet pressure were displayed and analyzed. Results show that surface roughness can have great effects on cavitation erosion intensity at standoff distances around the optimum and on erosion efficiency at standoff distances exceeding the optimum. The influence of surface roughness on cavitation erosion, adverse or advantageous, depends largely on the inlet pressure which determines the viscous sublayer thickness. More specifically, at inlet pressure of 10MPa and 15MPa, surface roughness value of 12.5μm is the best for achieving the strongest erosion intensity and maximum efficiency at standoff distance around 50mm; while at inlet pressure of 20MPa and 25MPa, roughness value of 6.3μm replaces 12.5μm to be the best one with the optimum standoff distance increased to 60mm. After standoff distance exceeds the optimum value, the specific energy consumption greatly increases, especially at relative lower inlet pressures, indicating a dramatic decrease of erosion efficiency. It can be concluded that excessive smooth surface is not conducive to the formation of cavitation bubbles, leading to an attenuated intensity of cavitation erosion; while excessive rough surface causes much energy dissipation and leads to divergent jets, resulting in a significant reduction of erosion intensity. According to the experimental results, there exists an optimum inner surface roughness value to achieve the strongest aggressive cavitation erosion capability for submerged cavitating jets.

Povezanost opšteg modela agresivnosti sa komorbiditetom antisocijalnog poremećaja ličnosti i bipolarnog afektivnog poremećaja

The General Aggression Model (GAM model) is a dynamic, social and cognitive development model that includes situational, individual and biological variables, based on the theories of social learning and social cognitive theories, as well as on a large number of theoretical and empirical arguments of many authors who are engaged in the study of aggression. The subject of our interest is the phenomenon of aggression in patients with bipolar affective disorder with the presence of antisocial personality disorder. The combined factors of aggressiveness in GAM model can be used to determine the presence, intensity or prediction of aggression in these patients. The General Aggression Model provides the division factors of aggressiveness into direct and indirect, such as personality factors, situations, environmental factors and biological factors.

A dear enemy relationship in a territorial cichlid: evidence for the threat-level hypothesis

Despite competing for resources such as space, food and mates, many territorial animals are less aggressive towards neighbours who rarely go beyond their territorial boundaries. This so-called dear enemy phenomenon is advantageous in territorial defence, but it has not been well studied in fish. In this work, we tested the ‘correct–incorrect boundary paradigm’ of the dear enemy phenomenon using the territorial cichlid fishNeolamprologus pulcher, which exhibits dear enemy relationships. When the fish was placed in a small experimental tank, in which fish established its territory, it was initially very aggressive against a neighbouring fish in an adjacent tank, but the aggression level decreased rapidly (within 4 days). When the tank containing the neighbour was shifted to the opposite side, the focal fish was more aggressive than the day before, but it exhibited less aggression than it did against a stranger placed on the shifted side. This lower level of aggression suggested that the focal fish did not regard the shifted neighbour as a stranger. Our observations provide support for the threat-level hypothesis, according to which territory owners will modulate aggression intensity based on the threat level.

Sexual Dimorphism and Geographic Variation in Dorsal Fin Features of Australian Humpback Dolphins, Sousa sahulensis.

Determining the sex of free-ranging cetaceans can be challenging. Sexual dimorphism among external features may allow inferences on sex, but such patterns may be difficult to detect and are often confounded by age and geographic variation. Dorsal fin images of 107 female and 54 male Australian humpback dolphins, Sousa sahulensis, from Western Australia (WA) and Queensland (QLD) were used to investigate sex, age and geographic differences in colouration, height/length quotient and number of notches. Adult males exhibited more dorsal fin notches (p<0.001) and a significantly greater loss of pigmentation on the upper half of their dorsal fins (p<0.001) than did adult females. These differences likely reflect that males experience a higher frequency and/or intensity of intraspecific aggression than females. In QLD, heavily spotted dorsal fins were more frequent among females than males (p<0.001). Logistic regression analyses revealed that dorsal fin spotting and loss of pigmentation on the upper half of the dorsal fin provided the best model parameters for predicting the sex of sampled adults, with 97% accuracy. This technique offers a rapid, non-invasive method for predicting sex in Australian humpback dolphins, which could potentially be applied to populations throughout their range. In contrast to adults, presumed immature animals showed little or no loss of pigmentation or spotting; however, the rate of development of these features remains unknown. There were pronounced differences between QLD and WA in the intensity of spotting on dorsal fins and the extent of pigmentation loss around the posterior insertion and trailing edge of the dorsal fin. While based on a limited sample size, these geographic differences may have conservation implications in terms of population subdivision and should be investigated further.

Virulence and aggressiveness of Phytophthora infestans isolates collected in Poland from potato and tomato plants identified no strong specificity

Late blight is a devastating and worldwide potato and tomato disease caused by Phytophthora infestans (Mont.) de Bary. The aim of the study was to compare P. infestans isolates collected from potato and tomato plants by determining their virulence, aggressiveness, and sporulation intensity on both hosts in reciprocal testing with the goal of elucidating possible host specialization of the pathogen. Isolates were multiplied on leaflets of their primary hosts. In total, 76 potato-derived P. infestans (P) isolates and 100 tomato-derived P. infestans (T) isolates collected from 2005 to 2007 were studied in detached-leaflet assay experiments. Virulence was assessed on Black’s potato differentials R1–R11 and cv. Bzura, as well as on the set of six tomato genotypes, namely cv. New Yorker (Ph-1 gene), Solanum pimpinellifolium L 3708 (Ph-3), West Virginia’63 (Ph-2), West Virginia 700 (Ph-1, Ph-2), Ottawa 30 (Ph-1, Ph-2), and BALU-30 (Ph-1, Ph-2, fruit resistance). Aggressiveness scored as disease severity and sporulation intensity assessed on a 0–3 grade scale were evaluated on leaflets of susceptible cultivars of both hosts. All 176 of the tested isolates were pathogenic to both hosts, indicating that extreme host specialization has not occurred. However, we did observe differences between P and T virulence spectra and their race structures supporting the notion of host adaptation of P. infestans. P and T isolates were more frequently virulent to differentials of their own hosts. P isolates had higher sporulation intensity on their own hosts than on tomato hosts, while for T isolates a similar sporulation intensity was observed on both hosts. Significantly stronger severity of the disease development on T testers was evoked by T isolates. All isolates showed stronger aggressiveness on susceptible potato than on susceptible tomato hosts, and the latter finding indicates a relatively greater suitability of potato host tissue for P. infestans pathogenicity. The host adaptation observed in this study was not conditioned by an ability to evoke disease, but rather by quantitative differences in pathogenic fitness. Genetic characterization of P and T populations is needed to place the present findings in a fuller context.

Variability in individual rates of aggression in wild gray seals: fine-scale analysis reveals importance of social and spatial stability

Aggressive interactions are costly for individuals in time, energy, or physical damage, and in polygynous mating systems, there is high variability in the rates and intensity of aggression across individuals and within breeding seasons. However, examinations into the drivers of this variability are often conducted in isolation, in non-wild systems, or the predictor variables in question, for example, dominance, are averaged across large spatial, social, or temporal scales. The aim of this study was to adopt a fine spatial and temporal scale approach to investigate the factors associated with inter-individual variation in aggression in wild, breeding male gray seals within three consecutive breeding seasons. To do this, we fit models examining if the daily frequency of aggression and probability of escalated aggression for males was best explained by factors such as dominance score, proximity to competitors or females, local social stability, and the occurrence of stochastic environmental events. Stability of neighbor identities was the strongest correlate of reduced male aggression. Dominance status did not correlate with aggression at the daily scale, with the exception of one period after a natural disturbance to the breeding colony where dominant males had relatively reduced rates of aggression. These findings emphasize the importance of local social stability in explaining inter-individual variation in aggression in a wild population and suggest that factors associated with aggression are context dependent in relation to the natural environment. Furthermore, we highlight the utility of a fine temporal scale and incorporating spatial parameters when investigating variability in aggression in wild systems.

The relationship between perch type and aggressive behavior in the lizard Norops polylepis (Squamata: Dactyloidae)

The intensity of aggression against intruders by owners of a territory has been related to the type of resources available to an individual within its territory. The influence of perch-site characteristics on aggressive behavior of resident male Norops polylepis in presence of an intruder male was investigated in this study. At each perch site, pairwise encounters were conducted in which the aggressive behavior of resident males was recorded, along with the diameter of the perch and the number of nearby perches. Aggressive behavior of resident males increased on larger perches and to some extent in areas having greater density of nearby saplings. Potential explanations for the high aggressive behavior of N. polylepis on broad perches with high number of neighboring saplings are explored.

Does a short-term increase in testosterone affect the intensity or persistence of territorial aggression? — An approach using an individual's hormonal reactive scope to study hormonal effects on behavior

In this study, we describe an approach based on an individual's hormonal reactive scope to study short-term effects of hormones on behavior. The control of territorial aggression has been traditionally linked to testosterone. Males of some vertebrate species show an increase in testosterone during territorial interactions and implantation studies suggest that such an increase in testosterone enhances the intensity and persistence of aggression. Here, we tested whether a short-term maximum release of testosterone – based on an individual's hormonal reactive scope – affects the intensity or persistence of territorial aggression in male black redstarts, a bird species in which testosterone does not increase during territorial encounters. An injection with gonadotropin-releasing-hormone (GnRH) induced a physiological peak in plasma testosterone that was specific for each individual (=individual reactive scope). However, such short-term surges in an individual's testosterone concentration did not affect the intensity or persistence of aggression. In conclusion, this study demonstrated (1) that a species that naturally does not increase testosterone during male–male encounters would not benefit from such an increase in terms of being more aggressive, (2) that behavioral studies using GnRH-injections represent a promising approach to study species differences in androgen responsiveness, and (3) that injections of releasing or tropic hormones in general may be a suitable approach to study short-term influences of hormones on behavior. These injections effectively mimic the potential short-term changes in hormones that can occur in the real life of individuals and enable us to study the effects of hormonal changes on behavior or other traits within an ecological and evolutionary framework.

The Art of Communication Through Drawing: The Case of "Mr. R," a Young Man Professing Misanthropy While Longing for Connection With Others

This case study reports the psychotherapy process of "Mr. R," who was 18 years old at the time when the therapy started. A total of 10 sessions were held in a period of six months. As the therapist, I was still at an early stage in my career, in the process of forming an integrative approach, which values an authentic and genuine therapeutic relationship with the client on the one hand, and the client’s adjustment to his living environment, on the other. Mr. R initially presented intense aggression and violence toward his family. He had been given a diagnosis of personality disorder, possible schizoaffective disorder, and atypical mental illness by different psychiatrists who had seen him. Because a past attempt with conventional talking therapy and pharmacological treatment did not produce positive results, I attempted to create a therapeutic relationship characterized by genuineness and authenticity, and I used Mr. R's drawings to help him express his emotions. The series of drawings that he created are presented in the article. These depict historical figures who parallel the therapeutic changes that occurred. Over the course of therapy, Mr. R's aggression was alleviated and he started relating to me not through hostility, but through his need for contact and respect. After termination, Mr. R's family members informed me that he had found peace with himself since therapy. I explain the reasoning behind my rather unconventional treatment decisions in terms of (a) contexts surrounding the practice of psychotherapy in Japan at that time; (b) the particular needs at that time of Mr. R, who had dropped out of all his previous treatment; and (c) other factors associated with Mr. R and his family.

THE ROLE OF SOCIAL AND PSYCHOLOGICAL CHARACTERISTICS OF A PERSON IN THEIR EXTREMIST AND TERRORIST THREAT EXPERIENCE

This article analyzes the role of social and psychological characteristics of an individual in their experience of threat of extremism and terrorism. A brief review of the work of authors involved in the study of this subject is presented. The article also describes contradictions that determine the research problem . The objective of the work is to study the relationship of extremist and terrorist threat experience and socio-psychological characteristics of a person from a regional perspective (terrorist activity in the region). Methods applied are as follows: theoretical analysis (analysis of scientific literature, synthesis, interpretation), empirical methods (questionnaires, survey), statistical treatment (correlation analysis by Spearman, Mann-Whitney test, multiple regression analysis, cluster analysis). The result of empirical research conducted in Penza and Volgograd showed that the individual experience of extremist and terrorist threat is due to different degree of intensity of empathy, altruism, aggression and sensitivity to terrorist threat, susceptibility to anti-democratic ideology, expectation of a positive attitude towards themselves and life sense making. The paper presents and describes «destructive№, «accepting», «adaptive», «denying» and «uncomfortable» types of extremist and terrorist threat experience. Scope of results application: social psychology, psychology of extremism, psychology of stressful situations experience.

Interspecific territoriality in two songbird species: potential role of song convergence in male aggressive interactions

In animals, interspecific interference competition is often associated with their aggressive behaviour. The intensity of interspecific aggression and the outcomes of interference competition between closely related species might be substantially modified by copying of vocal signals used in territory defence. Here we tested the hypothesis that song convergence observed in a secondary contact zone of two songbird species, the common nightingale. Luscinia megarhynchos, and the thrush nightingale, Luscinia luscinia, might be an adaptive response to interspecific interference competition. These species are morphologically and ecologically very similar. However, the thrush nightingale is slightly larger and several lines of evidence indicate its competitive dominance. In the secondary contact zone most thrush nightingales incorporate common nightingale song types in their repertoires. Using playback experiments, we evaluated the strength of nonvocal aggressive responses of both species to conspecific and heterospecific stimuli. The species did not differ in aggressive responses to a heterospecific stimulus, suggesting that competitive dominance is not associated with higher interspecific aggressiveness in nightingales. Interestingly, while the common nightingale reacted significantly more aggressively to the conspecific than the heterospecific stimulus, the thrush nightingale showed similarly strong responses to both stimuli. We suggest that this similar level of interspecific and conspecific aggression in the thrush nightingale results from mixed singing of this species in sympatry, as males may not distinguish conspecifics from heterospecifics by song alone. Our results are consistent with the concept of convergent agonistic character displacement. According to this theory, vocal convergence might be adaptive in species that overlap broadly in resource use, as it leads to better distinction of territory boundaries between the species and thus reduces the level of interspecific competition.

Does Innovation Success Influence Social Interactions? An Experimental Test in House Sparrows

AbstractIn group‐living animals, individuals may benefit from the presence of an innovative group‐mate because new resources made available by innovators can be exploited, for example by scrounging or social learning. As a consequence, it may pay off to take the group‐mates' problem‐solving abilities into account in social interactions such as aggression or spatial association, for example because dominance over an innovative group‐mate can increase scrounging success, while spatial proximity may increase the chance of both direct exploitation and social learning. In this study, we tested whether the individuals' innovation success influences their social interactions with group‐mates in small captive flocks of house sparrows (Passer domesticus). First, we measured the birds' actual problem‐solving success in individual food‐extracting tasks. Then, we manipulated their apparent problem‐solving success in one task (by allowing or not allowing them to open a feeder repeatedly) while a new, unfamiliar group‐member (focal individual) had the opportunity to witness their performance. After this manipulation, we observed the frequency and intensity of aggression and the frequency of spatial associations between the focal individuals and their manipulated flock‐mates. Although flock‐mates behaved according to their treatments during manipulations, their apparent problem‐solving success did not affect significantly the focal individuals' agonistic behaviour or spatial associations. These results do not support that sparrows take flock‐mates' problem‐solving abilities into account during social interactions. However, focal individuals attacked those flock‐mates more frequently that had higher actual problem‐solving success (not witnessed directly by the focal individuals), although aggression intensity and spatial association by the focal birds were unrelated to the flock‐mates' actual success. If this association between flock‐mates' actual innovativeness and focal individuals' aggression is not due to confounding effects, it may imply that house sparrows can use more subtle cues to assess the group‐mates' problem‐solving ability than direct observation of their performance in simple foraging tasks.

Contest experience enhances aggressive behaviour in a fly: when losers learn to win.

In several animal species, aggressive experience influences the characteristics and outcomes of subsequent conflicts, such that winners are more likely to win again (the winner effect) and losers more likely to lose again (the loser effect). We tested the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae), as a model system to evaluate the role of the winner and loser effects in male-male territorial contests. Further, we conducted experiments to test if winning and losing probabilities are affected only by the outcome of the previous contests, or whether the fighting experience itself is sufficient to induce an effect. Both winners and losers of two consecutive encounters displayed higher intensity of aggression and fought longer in subsequent contests. In both cases, they achieved higher fighting success than naïve males. The enhanced fighting performance of both winners and losers was stimulated by merely experiencing a contest, not necessarily by the relative outcome of previous fights. Overall, this study highlights the fact that previous victories and defeats both enhance aggressive behaviour in olive fruit flies, allowing them to achieve higher fighting success in subsequent contests against inexperienced males.

Seeking Clarity in a Linguistic Fog: Moderators of the Workplace Aggression-Strain Relationship

This study used cross-sectional data from 579 nurses to examine main and interaction effects of workplace aggression and theoretical nuances on employee strain. Perceived intensity of aggression and intention attributions by the target, power of the perpetrator in relation to the target, and perceived visibility of aggression by the target all served to exacerbate various relationships of workplace aggression with depression, physical symptoms, job satisfaction, and accidental contagious disease exposure. Three-way interactions reveal that these moderators may have complex roles in workplace aggression–strain research. This research supports a model where workplace aggression and its distinct moderators jointly impact employee strain and provide clarity to questions left unanswered due to term fragmentation and measurement overlap that currently obscure how mechanisms underlying workplace aggression constructs impact employee strains.

Single aggressive interactions increase urinary glucocorticoid levels in wild male chimpanzees.

A basic premise in behavioural ecology is the cost-benefit arithmetic, which determines both behavioural decisions and evolutionary processes. Aggressive interactions can be costly on an energetic level, demanding increased energy or causing injuries, and on a psychological level, in the form of increased anxiety and damaged relationships between opponents. Here we used urinary glucocorticoid (uGC) levels to assess the costs of aggression in wild chimpanzees of Budongo Forest, Uganda. We collected 169 urine samples from nine adult male chimpanzees following 14 aggressive interactions (test condition) and 10 resting events (control condition). Subjects showed significantly higher uGC levels after single aggressive interactions compared to control conditions, likely for aggressors as well as victims. Higher ranking males had greater increases of uGC levels after aggression than lower ranking males. In contrast, uGC levels showed no significant change in relation to aggression length or intensity, indicating that psychological factors might have played a larger role than mere energetic expenditure. We concluded that aggressive behaviour is costly for both aggressors and victims and that costs seem poorly explained by energetic demands of the interaction. Our findings are relevant for studies of post-conflict interactions, since we provide evidence that both aggressors and victims experience a stress response to conflict.

Le rôle des contraintes dans l’évolution des sociétés de macaques

N’existe-t-il aucune limite aux formes des systèmes sociaux que les animaux peuvent produire pour s’adapter à leur environnement, ou bien des contraintes définissent-elles l’espace des possibles, restreignant les systèmes sociaux à un nombre fini de formes ? L’étude des sociétés de macaques révèle qu’elles sont constituées par un ensemble de traits covariants. Le niveau d’asymétrie des conflits, l’intensité de l’agression, la fréquence des réconciliations, le degré de permissivité de la mère, l’importance des liens de parenté ou le tempérament individuel varient de manière corrélée d’une espèce à l’autre. Le couplage des traits comportementaux à différents niveaux du génotype et du phénotype a pour effet de circonscrire les macaques à un nombre limité de styles sociaux. Ceux-ci s’ordonnent sur une échelle à quatre degrés allant d’espèces caractérisées par des relations sociales intolérantes et de strictes hiérarchies, à d’autres dont les sociétés sont plus tolérantes et les rapports de dominance moins inégaux. Les différences interspécifiques observées dans le style social des macaques ne s’expliquent pas par des variations du milieu. En revanche, l’échelle de tolérance sociale montre une forte corrélation avec la phylogenèse des macaques, ce qui révèle que le coeur du système d’interconnexions particulier à chaque espèce n’a pas été modifié depuis plusieurs centaines de milliers d’années. Ces résultats nous apprennent que les liaisons entre traits comportementaux agissent comme des contraintes qui limitent la réponse évolutive des systèmes sociaux aux pressions écologiques. Résumé

Aggression Levels Affect Social Interaction in the Non‐Breeding Territorial Aggression of the Weakly Electric Fish, Gymnotus omarorum

AbstractAnimals typically decide whether to fight or retreat from conspecifics based on their individual estimates of the costs and benefits of fighting. Theoretical models predict how contenders solve a conflict, but the evaluation processes involved in these decisions depend on multiple factors that are difficult to explore experimentally. We addressed these questions using the non‐breeding territorial aggression of Gymnotus omarorum, in which subordinates make three distinctive decisions to signal their submission during a fight: (1) interruption of their electric discharges to hide from the dominant, (2) stop attacking and retreat, and (3) emission of ‘chirps’, transient submissive electric signals. We confirmed that subordinates take into account the aggressive performance of dominants to shape their own agonistic decisions and performance. The intensity of aggression is highly correlated with an agonistic dyad, and the decision of subordinates to retreat is influenced by the attack rates of dominants. When we lowered the aggression of expected dominants with a 5‐HT1A receptor agonist, the correlation between the two contenders' aggression levels was lost and subordinates completely stopped emitting electric chirp signals. The aforementioned results contribute to the understanding of the decision‐making strategies driven by social challenge inherent to agonistic encounters.

Comparing the Effects of Real Versus Simulated Violence on Dream Imagery

Participants in the current study were 75 males, including 25 Canadian soldiers, 25 heavy gamers who play military based video games such as "Call of Duty," and a control group comprised of 25 males. One dream per participant was analyzed using Hall and Van de Castle content analysis guidelines, including aggression, threat, and previously established scales for intensity of aggression and emotion. The dreams of soldiers had a higher frequency of both aggression and threat, and were also more intense in aggression and emotion than both the heavy gamers and the controls. These findings suggest that exposure to real life violence and threat (as well as the emotional significance of the experience) is more frequently incorporated into dream imagery than simulated or virtual threat. Limitations and directions for future studies are discussed.

Mates of Competitive Females: The Relationships between Female Aggression, Mate Quality, and Parental Care

Though rarely mate-limited, females in a wide variety of species express traits commonly associated with mate competition in males. Recent research has shown that these competitive traits (ornaments, armaments, and intense aggression) often function in the context of female-female competition for nonsexual reproductive resources and are often positively related to reproductive success. Increased success could occur because competitive females acquire limited ecological resources (nest sites, territories, etc.) or because they pair with high quality males, that is, older, more ornamented, or more parental males. Further, males paired with aggressive/low care females may compensate by increasing their paternal efforts. Here, I examined patterns of social pairing and parental care in free-living dark-eyed juncos (Junco hyemalis), a biparental songbird. I found no detectable relationship between female competitive behavior (aggression) and male quality (age, size, or ornamentation) or male provisioning. Thus, neither of the mate choice hypotheses (females compete for males or males prefer aggressive females) was supported. Instead, these results suggest that females compete for nonsexual resources and mate quality is a secondary consideration. I also found a negative relationship between male and female provisioning rates, suggesting that partners adjust their level of parental effort in response to their partner’s efforts.

Heightened aggression and winning contests increase corticosterone but decrease testosterone in male Australian water dragons

Water dragons (Intellegama [Physignathus] lesueurii) are large (to >1m) agamid lizards from eastern Australia. Males are fiercely combative; holding a territory requires incessant displays and aggression against other males. If a dominant male is absent, injured or fatigued, another male soon takes over his territory. Our sampling of blood from free-ranging adult males showed that baseline levels of both testosterone and corticosterone were not related to a male’s social tactic (territorial versus non-territorial), or his frequency of advertisement display, aggression, or courtship behavior. Even when we elicited intense aggression by non-territorial males (by temporarily removing territory owners), testosterone did not increase with the higher levels of aggression that ensued. Indeed, testosterone levels decreased in males that won contests. In contrast, male corticosterone levels increased with the heightened aggression during unsettled conditions, and were higher in males that won contests. High chronic male–male competition in this dense population may favor high testosterone levels in all adult males to facilitate advertisement and patrol activities required for territory maintenance (by dominant animals), and to maintain readiness for territory take-overs (in non-territorial animals). Corticosterone levels increased in response to intense aggression during socially unstable conditions, and were higher in contest winners than losers. A positive correlation between the two hormones during socially unstable conditions suggests that the high stress of contests decreased androgen production. The persistent intense competition in this population appears to exact a high physiological cost, which together with our observation that males sometimes lose their territories to challengers may indicate cycling between these two tactics to manage long-term energetic costs.