Dynamics and Spatial Distribution of Migratory Birds [antikvár]

Introduction Bird migration is one of the most exciting phenomena of our hving world, and therefore it is not surprising that it has been the subject of investigation since ancient times. Each year an estimated 50,000 million birds travel somewhere in the world. Short-distance migrants may just leave their mountainous breeding areas to seek milder winter conditions in the nearby foothills whereas long-distance migrants often cover tens of thousands of kilometres (Alerstam 1990). The principal migratory routes for many species of passerines migrating from the Europe to African wintering sites are fairly well known. What is missing is a detailed analysis of environmental factors controlling bird migration as well as the temporal and spatial course of the migratory journeys (Bairlein 1997, Tieleman 2007). Palearctic-Afiican migratory bird populations have to defeat several ecological barriers, like seas and deserts during the migration in post-breeding season and spring. During the migration driven natural selection population-specific strategies (e.g. habitat selection, food preference, fat deposition, migratory direction, migratory speed and dynamic, intra- and inter-specific competition, moult timing, etc.) and control mechanisms (e.g. photoperiodicity of hormonal system, nervous system and orientation, etc.) have evolved. The migration dynamics involves the evolution of the number, time and duration of the stopover of the migratory population on a territory for feeding or resting (Berthold 1993, Rappole & Jones 2002). Many species of European bird species are currently undergoing rapid declines, but some birds have increasing and expansive populations (BirdLife 2004). The causes of these changes are not clear but factors like habitat fragmentation, agricultural technology, hunting and global climate change known to be seriously affecting certain European bird populations. Monitoring is essential for the identification of ecological and conservation problems affecting birds. According to the EC Birds Directive on the protection of European bird population, all European Community countries have an obligation to monitor bird population. In Annex V of the directive, specific reference is made to use bird ringing for the monitoring of population levels of migratory bird species. Birds are particularly good subjects for population monitoring because they are sensitive indicators of habitat changes. Annual counts of birds tell us how numbers are changing, but bird ringing is needed if we want to understand the mechanism of the observed changes.