Abstract: Abstract   We present here an attempt to understand behaviors of dominant individuals and of subordinate individuals as behavior strategies in an asymmetric “hawk-dove” game. We assume that contestants have perfect information about relative fighting ability and the value of the resource. Any type of asymmetry, both relevant to and irrelevant to the fighting ability, can be considered. It is concluded that evolutionarily stable strategies (ESSs) depend on the resource value (V), the cost of injury (D), and the probability that the individual in one role will win (x). Different ESSs can exist even when values of V, D, and x are the same. The characteristics of dominance relations detected by observers may result from the ESSs that the individuals are adopting. The model explains some characteristics of dominance relations, for example, the consistent outcome of contests, the rare occurrence of escalated fights, and the discrepancy between resource holding potential (RHP) and dominance relations, from the viewpoint of individual selection.

Abstract: This simulation study explores some conditions leading to transitivity within dominance orders. Combinations of three parameters were varied to study their consequences upon hierarchy formation and upon the degree of linearity of resultant structures. The factors studied were (i) the importance of initial Resource Holding Potentials (RHPs) , (ii) changes brought in RHPs by successive victories and defeats, and (iii) accuracy of RHP assessment made by opponents. Results show that initial differences in RHP always lead to perfectly transitive chains whose rank order reflects the importance of initial differences. Even when simulated animals make important errors while assessing each other during round robin tournaments, emerging dominance structures are perfectly linear and ranks obtained in the structure are highly correlated with initial values in RHPs. Moreover, accumulated experiences of victory and/or defeat alone always lead to perfectly linear hierarchies. Their combination with initial individual differences in RHP led to the same conclusion. Even when assessment was far from being perfect, not only perfect chains were formed but initial values in RHPs significantly influenced rank order when the contribution of victory and defeat to RHP was relatively unimportant. The higher the importance of victory and defeat to RHP as compared to that of initial RHP values, the lower was the correlation between initial RHP values and the ranks order reached by individuals in the resultant hierarchies. In general also, the lower the variation within initial RHPs, the lower was the correlation between initial RHPs and ranks in the hierarchy. At a given level of initial RHP dispersion, increasing the contribution of victory and defeat to RHP diminished the correlation between initial RHP values and obtained ranks. In addition, inaccurate assessment reduced the overall correlation, especially when dispersion of initial RHP values was low and the contribution of victory and defeat was high. These results shed some light on the controversy about the respective roles of initial individual attributes and that of patterns of resolution in the formation of animal hierarchies. We present the emergence of social order within closed systems as those simulated here as a case of self-organization.

Abstract: This study examines the role of observation during the formation of triads in female domestic hens. Results indicate that during hierarchy formation, a hen observing agonistic interactions and conflict settlement between its former dominant and a stranger uses this information when in turn confronted by the latter. Under a first condition (E, N = 15 triads), bystanders witnessed their prior dominant being defeated by a stranger before being introduced to them. In a second condition (C1, N = 16 triads), bystanders witnessed the victory of their prior dominant over a stranger. In a third condition (C2, N = 15 triads), bystanders witnessed two strangers establishing a dominance relationship before being introduced to their prior dominant and to a stranger the former had just defeated. The behavioural strategies of bystanders depended on the issue of the conflict they had witnessed. Bystanders of the E condition behaved as having no chance of defeating the stranger. They never initiated an attack against it, and upon being attacked, readily submitted in turn to the stranger. On the contrary, bystanders of the C1 condition behaved as having some chances against the stranger. They initiated attacks in 50% of cases, and won 50% of conflicts against the stranger. Under condition C2, bystanders first initiated contact with the strangers in only 27% of cases, which approximates the average of their chances for defeating the stranger. However, bystanders finally defeated the strangers in 40% of cases. These results suggest that bystanders of conditions E and C1 gained some information on the relationship existing between their prior dominant and the stranger and that they used it coherently, perhaps through transitive inference, thus contributing to the existence of transitive relationships within the triads. Alternate explanations are examined.

Abstract: Baboons' (Papio cynocephalus ursinus) understanding of cause-effect relations in the context of social interactions was examined through use of a playback experiment. Under natural conditions, dominant female baboons often grunt to more subordinate mothers when interacting with their infants. Mothers occasionally respond to these grunts by uttering submissive fear barks. Subjects were played causally inconsistent call sequences in which a lower ranking female apparently grunted to a higher ranking female, and the higher ranking female apparently responded with fear barks. As a control, subjects heard a sequence made causally consistent by the inclusion of grunts from a 3rd female that was dominant to both of the others. Subjects responded significantly more strongly to the causally inconsistent sequences, suggesting that they recognized the factors that cause 1 individual to give submissive vocalizations to another.

Abstract: Feral horses are social animals, which have to rely on survival strategies centered on the formation of cohesive social bonds within their bands. Many problems in the husbandry of social animals such as horses, are due to the fact that the limits of their adaptive abilities are exceeded. Evidence suggests that the fundamental social characteristics of domestic horses have remained relatively unchanged. The social structure, social strategies and social interactions were investigated (3 non-consecutive years, 24 hr per day for several weeks) in long term established groups of domestic horses (mares and geldings of all ages) and a few small introduced groups, kept in (semi)natural environments. The general aim was to investigate the social needs of domestic horses. The social life of domestic horses was characterised by long lasting bonds with preferred partners which were established and maintained by allogrooming, play, proximity and dominance behaviours. Bonding partners were mainly found within the same sex-age group, but adult geldings also bonded with sub-adult mares and geldings. Adult mares were clustered in a group, while the other animals formed a second group. Among the adult mares, subgroups according to reproductive state were formed. Individuals regulated their social network by interfering with interactions between other members of the herd, which in itself is complex. An intervention is a behavioural action of one animal that actively interferes with an ongoing interaction between a dyad with the apparent aim of altering that interaction. This was verified by post-hoc analyses of disturbed and undisturbed interactions. Interventions in allogrooming or play were performed significantly more often when at least one member of the initial dyad was a preferred partner of, or familiar to (within the small introduced bands) the intervener. The stronger the preferred association in allogrooming between the intervener and member(s) of the initial dyad, the higher the probability the intervener would displace one initial member and continue allogrooming with the other. Just five behaviours were extracted which reliably reflected the dominance relations among horses. Aggression with the hind quarters was used both offensively and defensively and therefore not suitable as a reliable parameter. Individual dominance relationships were related to social experience. The implications of these findings for horse husbandry were assessed. It is argued that the execution of affiliative behaviours may be rewarding in itself, and therefore always will be a highly motivated behaviour. It is shown that social positive physical interactions (allogrooming, play) with other horses is an ethological need and therefore indispensable in modern husbandry systems. Ethological needs are so important for the animal that husbandry systems that lack the possibilities to execute such behaviours will cause chronic stress. It is concluded that all horses need physical social contact, and that horses, which lack appropriate social learning experiences during ontogeny, may be hampered in their social functioning later in life. Solutions for problems, including dominance problems, in individual social housing and group housing are presented.