Autumn migration begins in late September to early October, and peaks in late October to early November. The 800 mile (1,200 km) crossing from Iceland to Ireland is probably the longest sea crossing undertaken by any swan species. Whooper Swans wintering in Britain have only a slightly shorter overseas flight, of 500 miles (800 km) from Iceland to landfall in northwest Scotland
The autumn migration period lasts around 8 weeks. The oversea crossing between Iceland and Britain/Ireland can take from around 13 hours to 4.5 days.
Departure for the breeding grounds occurs mainly in March and April.
Satellite-tracking of Whooper Swans in the mid 1990s found that the time taken to migrate between Britain & Ireland and Iceland ranged from 12.7 – 42.4 hours in autumn, and from 32 – 101 hours in spring.
Wintering sites in northern Britain and Ireland are important as landfall or departure areas. For instance, large staging flocks of up to 2,000 birds occur on the north coast of Ireland in autumn.