Navigation in context: grand theories and basic mechanisms

Among the movements of animals across the surface of our planet, the wide-ranging migratory journeys of birds and the smaller-scale foraging excursions of social (hymenopteran) insects provide some of the most intriguing examples of biological systems of navigation. Many sensory cues have been found to be involved in accomplishing these tasks, but how this sensory information is integrated into the animal's overall system of navigation has remained elusive. Several over-arching concepts such as sun- or star-based systems of astronavigation, E-vector-based spherical geometry, map-and-compass and bi-coordinate position-fixing schemes have been developed to account for the animals' performances. Although these metaphors have some heuristic value, they are potentially distracting and might obscure some of the most important computational strategies used by the brain. Moreover, these top-down approaches are especially inappropriate in trying to understand the evolutionary 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, study 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 being part of a general-purpose navigational toolkit, the various guiding mechanisms have most certainly arisen from an opportunistic grafting of particular special-purpose modules on to pre-existing sensory-motor control systems.