The iconic image of two swans with their necks entwined in the shape of a heart is one of the most recognisable symbols of love and devotion. But is this romantic gesture as meaningful as it appears, and is it true that swans really mate for life?
There are six living species of swans, the largest members of the waterfowl family Anatidae and among the largest flying birds. Four species – the mute swan, whooper swan, trumpeter swan, and Bewick’s swan – are native to the Northern Hemisphere. The black swan is found in Australia, and the black-necked swan inhabits South America. The mute swan has also been introduced to North America, Australia, and New Zealand.
Swans are generally monogamous, forming lifelong pair bonds. However, their breeding behaviour varies significantly between species.
Swans typically form pair bonds before reaching sexual maturity. For example, mute swans pair up during their second winter but do not begin breeding until they are around three years old. Trumpeter swans, on the other hand, form pair bonds at the age of two but delay breeding until they are between four and seven years old. In most cases, females are younger than males when the pair bond is formed.
Juvenile swans live in flocks until they reach sexual maturity and usually find their mate within the flock. Non-breeding pairs often mimic the behaviour of breeding pairs, displaying to each other, defending a defined territory, and even building partial nests. However, they tend to be less aggressive toward intruders compared to nesting birds, and in some cases, non-breeding pairs will alternate holding territories along the same stretch of water.
When a swan is ready to breed, it leaves its flock with its mate to establish a new territory. At this stage, the pair becomes more solitary, interacting only with each other.
The most common reason for a swan to change its mate is the death or disappearance of its previous partner. However, true “divorce”, where both original partners are known to be alive, does occur, albeit rarely.
A widely cited figure is that 3% of non-breeding mute swans and 9% of breeding pairs divorce. These figures come from a 1968 paper in Wildfowl journal published by the Wildfowl & Wetlands Trust (WWT). However, the paper notes that these numbers likely underestimate the true frequency of divorce, as they only account for divorces occurring from one breeding season to the next, and divorce even midway through a season has been known to occur.
Compared to other bird species though, the divorce rate among swans is relatively low. A rare instance of divorce was documented in 2010 at the WWT Slimbridge reserve involving two Bewick’s swans. Male swan Sarindi returned from his annual migration from Arctic Russia with a new partner, Sarind, instead of his mate of two years, Saruni. Shortly after, Saruni also arrived at the wetlands, this time with a new mate, Surune.
This unusual occurrence was only the second recorded case of divorce in 50 years of WWT research, which has tracked around 4,000 swan pairs at Slimbridge.
