Animal navigation at the end of the century: a retrospect and a look forward

Around the middle of the 20(th) century the discovery of the biological com passes - solar, lunar, stellar and magnetic - marked a fundamental breakthr ough in the study of the orientation and navigation of animals. This discov ery attracted a great number of scholars to this field of research, and con tributed to our knowledge of frequently recurrent phenomena such as zonal m aintenance in ecotonal environments and the guidance of migratory and forag ing movements. Several lines of research that emerged were pertinent to and continue to stimulate the study of the genetic and acquired components of orientation and its sensory foundations. The years in which the biological compasses were discovered also opened up the problem of the nature and func tion of animal maps, which are often integrated with the use of one or more compasses, and enable the animal to fix its position within a relatively e xtensive territory. The maps can derive from a direct knowledge of a geogra phical area, and are thus indicated as cognitive or mental, or they can ext end beyond the places already visited by the animal. Although this second t ype of map is probably widespread, it has been ascertained and analysed onl y in the homing pigeon. The olfactory nature of the pigeon's map has found confirmation in neuroethological studies, and in the discovery that quantit ative relations between certain organic substances dispersed in the atmosph ere characterise different geographical areas and show enough persistency o ver space and time to allow them to act as the material substrate for olfac tory navigation. Obstacles to progress in the field of animal navigation in clude what is still a poor level of knowledge about the mechanism of magnet ic reception and about the physiological effects of experimental magnetic t reatments, as well as the widespread but groundless opinion that animals po ssess a magnetic map. Progress in telemetric recording of routes, even over long distances, have made it possible to extend studies to new subjects an d new environments. The satellite monitoring of the movements of ocean-cros sing birds and sea turtles has begun to reveal a remarkable navigational ca pacity in both groups - a capacity based on mechanisms which are still unkn own.