On being asked to write a book on migration and homing in animals, intended as an introductory text to inform and stimulate both students and non-specialists, I saw the following alternatives for an outline: (1) I could discuss known or hypothetical mechanisms of orientation, and enumerate animals known or thought to use these mechanisms in migration and homing. (2) I could discuss the known feats of orientation by animals under field observation (e. g. migration), following some practic able order, with a subsequent discussion of the attempts at and possible success in elucidating the basic mechanisms of orientation. Both alternatives have obvious disadvantages. (1) would suffer from the fact (a) that very few orientation mechanisms (such as the sun, star, or magnetic compass) have been firmly established and (b) that for many animals the modes of orienta tion are unknown; therefore, for many animals whose consider able feats of orientation are well known, an appropriate alloca tion could not be made. With (2) the disadvantage is that due to the complexity of animal movements, it is difficult to find some relevant order and that in many animal groups discussions of certain known mechanisms such as the sun com pass would recur. I have selected outline (2) as the much lesser evil. The discussion pursues a compromise between taxonomic order and similarity in feats of orientation or methodological approaches chosen by the various investigators."

Seven years have elapsed between this and the preced- ing major symposium on animal orientation and naviga- tion, held on Wallops Island, Va., USA in 1970. Never before between two symposia in this field has there been such an enormous increase - more truly an explo- sion - of new data, new evidence, new ideas, and meth- ods. Moreover, environmental awareness has also in- creased tremendously. The essential role of animals as bio-indicators, the economic importance of dwindling stocks of fish, whales, and other animals demand in- creasing efforts to investigate their life cycles and whereabouts, and that means for many of them, their travels between breeding, feeding, or wintering ranges. Although many aspects of research in the various fields covered by this symposium qualify as basic research, environmental and economic considerations cannot be dismissed. Finally, there is a chance to eventually find biologic systems of migration and orientation that may be at least partially useful for human navigation or other undertakings. The diversity of species involved in animal migration and the methodologies employed in unraveling the modes of animal navigation provide the reader of this volume with a survey of the front line of research in this field, with emphasis on current ideas and with a fore- taste of the problems ahead. The reports offer insight into the experimental difficulties, sometimes formi- dable, that the researcher encounters when dealing with free-ranging animals.