The female (pen) lays up to seven eggs between late April and early May. Both sexes incubate the eggs, which hatch after 35-41 days. The young birds, or cygnets, sometimes ride on their parents' backs and remain with the adult birds for four or five months. Cygnets are generally dingy brown above and whitish below. Occasionally cygnets may be all white and are known as 'Polish swans'. The young of some pairs are driven off the breeding territory as soon as their plumage is predominantly white (during late autumn or winter). Other broods often accompany their parents to the wintering area, and usually join a large flock in which they remain when the parents return to their breeding territory. Young birds will not generally breed for the first two years of adult life.