Increasing numbers of wintering Cormorants of the race Phalacrocorax carbo sinensis in Öresund
Keywords:winter ecology, migration, bird ringing, bird banding, ringing recoveries, distribution, predation, predator-prey interaction
The Cormorant of the subspecies Phalacrocorax carbo sinensis has increased markedly in north-western Europe during the last decades. Most of the sinensis breeding in northern Europe migrate south in autumn with most birds wintering in the Mediterranean including the coast of North Africa. It has been known for a long time that birds from the Norwegian population of the subspecies carbo winter in coastal and offshore areas in southern Sweden, Denmark and the Baltic. During recent winters an increasing number of Cormorants have occurred in these waters and it is now believed that the increase has been caused partly by a change in the winter distribution of North European sinensis. In this paper I describe the increase in southern Öresund between Denmark and Scania. I also present data on winter recoveries from these and adjacent waters of sinensis birds ringed in Sweden. I suggest that the increase may depend on the abundance of herring or perhaps other shoaling fishes. I estimate that the large winter flock consume about 120 tons in December–January, which is 0.07% of the herring population in a peak year.
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