Swans form monogamous pair bonds that last for many years, and in some cases these bonds can last for life. Their loyalty to their mates is so storied that the image of two swans swimming with their necks entwined in the shape of a heart has become a nearly universal symbol of love.
Why birds mate for life isn't as romantic as it first appears, though. Considering the time needed to migrate, establish territories, incubation, and raising their young, spending extra time to attract a mate would minimize reproductive time. One of the benefits of mating for life is that the swan duo learns from their successes and failures each time they raise cygnets, reports the BBC.