Swans – as well as ducks and geese – are members of the Anatidae family, in the order Anseriformes.
With its elegant long neck, the black swan (Cygnus atratus) is one of New Zealand’s largest wetland birds, around 1.2 metres long and weighing 5–6 kilograms. On the water, it appears all black with a bright red bill; however, in flight the bird shows wide white trailing wing margins. It has a bugle-like call, and hisses to defend its nest.
Native or introduced?
About 100 black swans were brought to the South Island from Australia in the 1860s, and the species has traditionally been regarded as introduced. However, numbers increased faster than expected, suggesting more birds arrived independently – in which case it should be considered a self-introduced native.
To add to the intrigue, the extinct native swan, previously named Cygnus sumnerensis, is now thought to have been the same species as the black swan.
There are 10 main regional populations of black swans. The overall estimate is around 60,000 birds, down from 100,000 in the early 1960s. Lake Ellesmere (Te Waihora) alone had around 70,000 until the fierce Wahine storm of 1968 destroyed the lake-floor vegetation, causing swan numbers to crash. Large numbers gather at Farewell Spit each winter to moult.
Black swans mainly eat the leaves of aquatic plants, which they reach underwater with their long necks, tail up-ended like a mallard. They also graze on clover and pasture close to lakes, where manure fouling makes them unpopular with farmers.
Black swans breed either in pairs or in colonies. Their nests are huge mounds of long foliage, built near lake edges. Females may lay up to 14 green eggs, but six is the average. In colonies, up to 40 cygnets gather in large crèches guarded by a few adults.
Juveniles leave their natal lake and spend several years in estuarine or coastal sites, returning to take up permanent residence once they reach breeding age – between two and four years old. Not all birds breed every year. The oldest known swan in New Zealand was at least 29.
Black swans are partially protected, and are hunted in season according to regional limits. About 5,000 are shot each year.