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BiologyWhooper swans can be seen in Britain from November to March (3). During the migration they fly at high altitudes; a pilot flying at 8,000 feet once saw a flock of swans, thought to be whoopers (6). Although this species may occur in very large flocks numbering over 1000 individuals, they more typically occur in small groups (5). They feed on water plants, grass and cereals and may eat waste potatoes and sugar beet (5). During courtship, pairs face one another, with the wings held in a half-lifted and half-open position. The neck is then extended and bent repeatedly while both birds loudly vocalise (7). The pair produces a clutch of between three and seven eggs, which are incubated for 35 days. The young, known as cygnets, will have fully fledged after a further 87 days (3).