  Background: Recent research in animal behaviour has contributed to determine
how alignment, turning responses, and changes of speed mediate flocking and
schooling interactions in different animal species. Here, we address
specifically the problem of what interaction responses support different
nearest neighbour configurations in terms of mutual position and distance.
Results: We find that the different interaction rules observed in different
animal species may be a simple consequence of the relative positions that
individuals assume when they move together, and of the noise inherent with the
movement of animals, or associated with tracking inaccuracy. Conclusions: The
anisotropic positioning of individuals with respect to their neighbours, in
combination with noise, can explain several aspects of the movement responses
observed in real animal groups, and should be considered explicitly in future
models of flocking and schooling. By making a distinction between interaction
responses involved in maintaining a preferred flock configuration, and
interaction responses directed at changing it, we provide a frame to
discriminate movement interactions that signal directional conflict from those
underlying consensual group motion.
