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

One striking aspect of certain types of animal assemblages, for example fis h 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 we ll, the evolution of spatial regularity and the high levels of synchrony th at typify the groups in which certain animals move ore less clear. Traditio nal explanations have generally focused on benefits gained during interspec ific interactions, particularly the improvement of antipredator responses, or have suggested aero- or hydrodynamic advantages during locomotion. Howev er, since the latter benefits of structural regularity may be largely rejec ted on theoretical grounds, and because many examples of spatially regular, synchronous groupings - such as dusk-flying flocks of some birds - may occ ur in the absence of predators, se suggest that these behaviours may not be explained solely in terms of locomotory efficiency or performance in preda tor-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 ampl ifiers of individual quality. The evolution of such behaviour therefore nee d not have occurred as a result of interspecific interactions, but could ha ve happened in the arena of conspecific evaluation.