"Swans feed in the water and on land. They are almost entirely herbivorous, although small numbers of aquatic animals may be eaten. In the water food is obtained by up-ending or dabbling, and their diet is composed of the roots, tubers, stems and leaves of aquatic and submerged plants.
Swans form monogamous pair bonds that last for many years, and in some cases these can last for life. Modern genetic techniques are starting to reveal that 'divorces' are more common than previously thought, as is mating with other swans outside of the social pairing, without breaking the social pair bond. These bonds are maintained year round" Wikipedia