Schooling, dusk flight and dance: social organisations as amplifiers of individual quality?

One striking aspect of certain types of animal assemblages, for example fish schools or bird flocks, is the level of synchrony and spatial regularity that group members achieve. Although the evolutionary mechanisms leading to the formation of animal aggregations appear to be understood reasonably well, the evolution of spatial regularity and the high levels of synchrony that typify the groups in which certain animals move are less clear. Traditional explanations have generally focused on benefits gained during interspecific interactions, particularly the improvement of antipredator responses, or have suggested aero- or hydrodynamic advantages during locomotion. However, since the latter benefits of structural regularity may be largely rejected on theoretical grounds, and because many examples of spatially regular, synchronous groupings - such as dusk-flying flocks of some birds - may occur in the absence of predators, we suggest that these behaviours may not be explained solely in terms of locomotory efficiency or performance in predator-prey interactions. Instead, we suggest that the maintenance of regular spatial positions and the level of synchrony achieved within certain social groups may reveal honest information about an individual's neurosensory or locomotory performance, and that these behaviours may have evolved as amplifiers of individual quality. The evolution of such behaviour therefore need not have occurred as a result of interspecific interactions, but could have happened in the arena of conspecific evaluation.