Whooper swans are one of the heavyweights of the bird world, with a wingspan of nearly 2.5m and weighing up to 11kg. They are one of the largest flying birds in the world. Whooper swans have an extensive geographic range and can be found within the boreal zone in Eurasia and many nearby islands. Some migratory populations can be found in India and western North America. Migrating whooper swans fly at altitudes of 500 to 1,700 m when crossing oceans, but often prefer flying at lower levels to allow for frequent breaks between flights. Near the British Isles, migrating whooper swans have been recorded reaching heights above 2,500 m.