All populations are migratory and winter mainly at sea, usually in estuaries and bays, but often well offshore where fish are within diving reach near shallow banks or islands [REF].
The nominate subspecies breeds from southern Sweden and Denmark through central and eastern Europe east to western Siberia, and winters mainly in the North and Baltic Seas, with smaller numbers in the Adriatic, Black Sea, Caspian Sea, Mediterranean and on inland lakes [REF].