The image of a pair of swans with their necks entwined in a heart shape is one of the best known symbols of love and devotion. But is this romantic gesture all that it seems and is true that swans mate for life?

Swans do form monogamous pair bonds that can last for many years and even for life. But divorce and adultery does happen; Australian black swans are particularly unfaithful with an estimated 1 in 7 eggs unwittingly reared by a male black swan that are not his.

Other species of swan will change partners after a poor breeding season or nest failure and they will usually seek out another partner if their mate dies. It tends to be female swans who are more successful at finding a new mate as they will rejoin a flock to find a new partner, whereas males will remain in their breeding territories hoping to attract a passing female.

There are a number of benefits of swans forming long-term pair bonds. The couple will not waste time looking for a new mate each year, conserving their energy after migration. Of all species of swan Bewick’s swans are least likely to divorce and it is no coincidence that they have the furthest and hardest migration of all swan species.

Swan husbands are thoroughly modern parents helping incubate eggs, raise chicks and defend the nest so for female swans it is not worth the risk of finding a second mate or even contracting a sexually-transmitted disease. Swan duos also learn from their mistakes each time they raise a new brood of cygnets meaning that as each year passes their chances of reproductive success increases.