ABSTRACT

The count of visible migrants at traditional bottlenecks, but also along minor migration corridors, has been the earlier approach to this research field, being the easiest possible method, just with the aid of binoculars and telescopes. The way in which bird populations migrate and spend different life stages in different geographical areas have been classified according to different categories. Among migrating raptors breeding in the Palearctic. several species travel thousands of kilometers twice a year between breeding and wintering areas with considerable energetic costs and high mortality risks. Time, energy and safety are the main currencies according to which a migratory journey is arranged: if a bird wants to save time, it must spend more energy but, on the other hand, saving energy and minimizing risks entails a higher consumption of time. Flocking can be observed in several species of migrating birds, as a behaviour underlying a social function.