Abstract: In primate groups, collective movements are typically described as processes dependent on leadership mechanisms. However, in some species, decision-making includes negotiations and distributed leadership. These facts suggest that simple underlying processes may explain certain decision mechanisms during collective movements. To study such processes, we have designed experiments on white-faced capuchin monkeys (Cebus capucinus) during which we provoked collective movements involving a binary choice. These experiments enabled us to analyse the spatial decisions of individuals in the group. We found that the underlying process includes anonymous mimetism, which means that each individual may influence all members of the group. To support this result, we created a mathematical model issued from our experimental data. A totally anonymous model does not fit perfectly with our experimental distribution. A more individualised model, which takes into account the specific behaviour of social peripheral individuals, revealed the validity of the mimetism hypothesis. Even though white-faced capuchins have complex cognitive abilities, a coexistence of anonymous and social mechanisms appears to influence their choice of direction during collective movements. The present approach may offer vital insights into the relationships between individual behaviours and their emergent collective acts.

Abstract: This study investigated the role of dominance and level of activity and exploration on leadership in zebra finches (Taenopygia guttata) searching for food. In pairs of zebra finches fairly matched in size and that experienced the same level of food deprivation, the same bird consistently reached first one foraging patch over several trials. The same pattern of arrival to food occurred when resources were provided in two distant patches available concurrently, a situation that would potentially allow subordinates a greater access to resources. In further testing, the formation of new pairs with the same birds led to several changes in leadership, indicating that leadership is not an absolute feature. The member of a pair that proved to be the most active and exploratory during independent, solitary trials became the leader in nearly all pairs tested. The same pattern held true in newly rearranged pairs where individuals often experienced changes in dominance status. Dominance failed to be associated with leadership in all tests. The results suggest that in a relatively egalitarian species, level of activity and exploration may be a stronger predictor of leadership than dominance.

Abstract: n a herd of semi-captive plains zebras interventions, which occurred within the harems, were investigated in order to answer the question why zebras interfered. These interventions are of interest because they regulate the contacts between companions and because, as corrective and preventive measures, they reveal the normative principles underlying the behaviours by which animals structure their social environment. An attempt was made to deduce 1) the internal norms of the interferer; 2) his short term aims; 3) his tactis and 4) his perception of the social environment. The analysis revealed that in the case of an affiliative interaction foals, yearlings and adult mares started to interfere if a friend had an affiliative contact with another zebra. In view of the interferer's behaviours it was concluded that their aim was to break off the ongoing interaction and that zebras tended to protect friendship bonds. Foals and yearlings further interfered if their mother was being threatened, attacked or sexually approached by a stallion. In view of the interferer's behaviours its aim was to prevent iminent interactions or to break off ongoing interactions. This suggests that these interventions were of a protective nature. The interferer's behaviours in both contexts ware very much alike. Mares tended to interfere if their foal/yearling or adult daughter was threathened or aggressed or if a mare friend was being sexually approached by a stallion. This type of intervention was of a protective nature. Stallions in a multi male harem showed a high tendency to interfere in courtship interactions. From the resemblance between interventions in courtship and in aggressive interactions it is concluded that, at leat in a number of cases, the individuals have perceived courtship behaviour by the stallion as a threat towards the mare involved.

Abstract: A common practice in studies of social animals is to rank individuals according to dominance status, which has been shown to influence access to limited resources and stability of social relationships, and may in turn correlate with reproductive success. According to the socioecological model for primates, most female dominance relationships are either nepotistic or virtually undetectable (egalitarian), with nepotistic species being philopatric, and dispersing females being egalitarian. Female mountain gorillas (Gorilla beringei beringei) disperse, and they have been characterized as being egalitarian, but previous studies have not examined their dominance relationships from a long-term perspective. We evaluated 15 matrices of displacement/supplantation interactions that spanned 30 years of observations in the Virunga Volcanoes region, and included 51 female mountain gorillas in six groups. Only 4% of displacements were directed against higher ranking females, and when matrices had less than 5% unknown dyads, linearity indices were consistently greater than 0.95. Therefore, previous results suggesting undetectable dominance relationships may have reflected an insufficient quantity of data for this species, rather than actual nonlinearity in its hierarchies. Dominance depended on age and group tenure rather than nepotism, yet some females maintained a high ranking for most of adulthood (15-25 years). Most rank shifts occurred through changes in group composition, rather than switches in established relationships. These results fit within growing evidence for linear individualistic hierarchies in some primates, often coupled with dispersal, as commonly found in ungulates. In light of these results, we propose that the dominance relationships of female mountain gorilla are best characterized as “Dispersal-Individualistic” instead of the previously suggested “Dispersal-Egalitarian”.

Abstract: Seven major types of sampling for observational studies of social behavior have been found in the literature. These methods differ considerably in their suitability for providing unbiased data of various kinds. Below is a summary of the major recommended uses of each technique: In this paper, I have tried to point out the major strengths and weaknesses of each sampling method. Some methods are intrinsically biased with respect to many variables, others to fewer. In choosing a sampling method the main question is whether the procedure results in a biased sample of the variables under study. A method can produce a biased sample directly, as a result of intrinsic bias with respect to a study variable, or secondarily due to some degree of dependence (correlation) between the study variable and a directly-biased variable. In order to choose a sampling technique, the observer needs to consider carefully the characteristics of behavior and social interactions that are relevant to the study population and the research questions at hand. In most studies one will not have adequate empirical knowledge of the dependencies between relevant variables. Under the circumstances, the observer should avoid intrinsic biases to whatever extent possible, in particular those that direcly affect the variables under study. Finally, it will often be possible to use more than one sampling method in a study. Such samples can be taken successively or, under favorable conditions, even concurrently. For example, we have found it possible to take Instantaneous Samples of the identities and distances of nearest neighbors of a focal individual at five or ten minute intervals during Focal-Animal (behavior) Samples on that individual. Often during Focal-Animal Sampling one can also record All Occurrences of Some Behaviors, for the whole social group, for categories of conspicuous behavior, such as predation, intergroup contact, drinking, and so on. The extent to which concurrent multiple sampling is feasible will depend very much on the behavior categories and rate of occurrence, the observational conditions, etc. Where feasible, such multiple sampling can greatly aid in the efficient use of research time.