Navigation in context: grand theories and basic mechanisms

Among the movements of animals across the surface of our planet, the wide-r anging migratory journeys of birds and the smaller-scale foraging excursion s of social (hymenopteran) insects provide some of the most intriguing exam ples of biological systems of navigation. Many sensory cues have been found to be involved in accomplishing these tasks, but how this sensory informat ion is integrated into the animal's overall system of navigation has remain ed elusive. Several over-arching concepts such as sun- or star-based system s of astronavigation, E-vector-based spherical geometry, map-and-compass an d bi-coordinate position-fixing schemes have been developed to account for the animals' performances. Although these metaphors have some heuristic val ue, they are potentially distracting and might obscure some of the most imp ortant computational strategies used by the brain. Moreover, these top-down approaches are especially inappropriate in trying to understand the evolut ionary design of an animal's navigational system. Instead, we must go back to basics, use modern recording technology to unravel the detailed spatial and temporal structures of migratory routes and foraging trajectories, stud y the animal's sensory and computational abilities by combining behavioural and neurophysiological, approaches, then work bottom-up, as volution did, by trying to integrate the individual navigational methods. Rather than bei ng part of a general-purpose navigational toolkit, the various guiding mech anisms have most certainly arisen from an opportunistic grafting of particu lar special-purpose modules on to pre-existing sensory-motor control system s.