Long-term Changes in Autumn Migration of Selected Soaring Bird Species at Burgas Bay, Bulgaria

The paper presents data of the autumn migration along the Western Black Sea migration route (Via Pontica) collected since 1979 with special attention to the changes of migration numbers and peak days of the ten most numerous soaring bird species. We found long-term increase in the migration numbers of Pelecanus onocrotalus, Ciconia ciconia, Ciconia nigra, Circaetus gallicus, Circus aeruginosus, Accipiter brevipes, Clanga pomarina, Aquila pennata and Falco vespertinus. All collected data confirm that the Burgas Bay is the place with the highest and increasing autumn migration numbers of the great white pelican and the red-footed falcon in Europe. Due to our long experience in migration observations, we introduce four new terms (flyshed, sandglass site, migration period and peak's migration period) and propose a classification of the sandglass sites according to the flight types and migration behaviour of the soaring birds. Additionally, we outline the need for covering of a wider segment of the migration route through a chain of observation points, including specialised radar and the usefulness of joint and synchronised efforts by all teams at the basic observation points in Europe and Asia Minor on a continental scale.