Black Swan Pair, Feeding, Victoria, Australia

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The black swan (Cygnus atratus) is a large and iconic Australian waterbird. They are native only to Australia and are found throughout the southern half of the continent. Mature black swans measure between 110 and 142 centimetres (43 and 56 in) in length and weigh 3.7–9 kilograms (8.2–19.8 pounds). Their wing span is between 1.6 and 2 metres (5.2 and 6.6 feet).

Black swans have the longest neck relative to their body size of any swan. They are nomadic within Australia, with erratic migration patterns that depend on climatic conditions. It is a monogamous breeder, with both partners sharing incubation and cygnet-rearing duties. Black swans are socially monogamous, generally mate for life, and remain devoted partners for many years. However, their relationships can have some surprising twists.

About around 6-10% of black swan pairs part ways even when both partners are alive, effectively divorcing one another. If one partner passes away, the surviving swan will often find a new mate. Despite being romantically bonded, they aren't always completely faithful. DNA studies show that about one in six cygnets are fathered by a male outside the pair bond. Finally, up to a quarter of all black swan pairings are same-sex couples, usually two males. These pairs often take over a nest or temporarily mate with a female to secure eggs, and they are highly successful at raising cygnets.