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Veränderungen im Zugverhalten des Kormorans Phalacrocorax carbo sinensis von den 1930er Jahren bis in die Gegenwart

From the north-eastern German breeding areas of the Great Cormorant (Mecklenburg-Western Pomerania, Brandenburg, Saxony, Saxony-Anhalt), ringing data are available for a period of more than 80 years. These data are unique for the Baltic Sea area. Cormorants were ringed as early as during the 1930s, and ringing was re-started after World War II in 1957. These ringing efforts resulted in a total of 2, 061 recoveries until October 31, 2014 (including both ring recoveries and re-sightings). This number includes 287 recoveries from the winter season (16 November – 15 February), being used for the present analyses. During the 1930s, three different migration routes could be distinguished: The south-eastern route, following the eastern coast of the Adriatic Sea down to Greece, in some cases even Turkey, the southern route, crossing Italy or Corsica/Sardinia to North Africa, and the western route to Western Europe. The proportion of birds using the south-eastern route started to decline during the 1980s. Currently, this migration route is abandoned. This development is related to the population increase and range expansion of the European breeding population since the beginning of the 1980s. Data from the Croatian Bird Ringing Centre show, that winter recoveries in recent times mainly refer to birds from the northern and eastern Baltic, whereas recoveries from the south-western Baltic (Denmark, Schleswig-Holstein and Mecklenburg-Western Pomerania) are missing. For the southern migration route, a decline of the migration distance is obvious. The mean co-ordinate of recoveries currently lies 740 km north of the mean co-ordinate found during the 1930s. Recoveries from North Africa have become rather exceptional in recent times. Recoveries from the western migration route spread over the whole continent from the Mediterranean to the Atlantic coast. The birds may reach southern Spain, Portugal and even Morocco. There was no significant change in migration distance from 1932/33 until 2009/10 ; however, recently (2010/11 to 2013/14) the distance has increased significantly. Simultaneously, the proportion of birds using this migration route increased. Wintering in areas near to the region of origin has increased since the 1980s. Recoveries within a distance of < 500 km from the reference point (i.e. the mean co-ordinate of the ringing sites) were rare until the 1980s, but after 1999/00 about one third of the Cormorants was recorded within this radius. Short distance migrants, however, usually do not remain in their regions of origin, but show a pronounced south-west migration. The trend of wintering in areas near to the region of origin corresponds temporally to the establishment of winter populations on the Baltic coast. Birds wintering on the Baltic Sea coast of Mecklenburg-Western Pomerania mainly originate from more northern or eastern Baltic areas (Denmark, Sweden, Finland, Estonia, Russia), and the proportion of East German birds recovered here during the winter season is low. Finally, another noticeable change is the use of inland sites for wintering. During the 1930s, the vast majority (94%) of wintering Cormorants was found in coastal areas. Since the 1980s, the proportion of birds recorded at inland sites exceeds 50%.

Zugverhalten; Phalacrocorax carbo sinensis

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