Researchers from the University of Otago have found New Zealand had its own species of black swan, the poūwa.
The study also revealed the bird was hunted to extinction, much like the fate of the moa, soon after humans arrived in the late 13th century.
Further analysis of ancient DNA and bone dimensions found the bird was much heavier and larger than first thought.
The researchers also found poūwa were on the way to becoming flightless when they became extinct.
Dr Nic Rawlence, Director of the Otago Palaeogenetics Laboratory, said the findings are one of a growing number of examples of extinction and colonisation since the arrival of people in New Zealand.
"One of the interesting findings comes from the highly elongated leg bones, which shows they were already on the path towards flightlessness," Dr Rawlence said.
"Birds seem to get these elongated legs in island ecosystems where there are no mammalian predators and the top predators are birds, like the extinct Haast's Eagle and Eyles' Harrier."
Dr Rawlence added it was thought that the extinction was brought on by Polynesian and Māori hunting.
"Until the mid-1990s, scientists thought that the black swans New Zealand had when Polynesians arrived were the same as the Australian ones we have now," he says.
"But when Europeans arrived in New Zealand in the late 18th century there were no [New Zealand] black swans [alive anymore], but they found their bones in pre-human fossil sites and archaeological deposits.
"We assessed museum and archaeological collections, and extracted ancient DNA in our laboratory, looked at bumps on bones and took bone measurements to characterise their shape."
Australian black swans first arrived in New Zealand during the Pleistocene Ice Age, an estimated one to two million years ago.
After settling on the main land and the Chatham Islands they grew to almost twice the size of the Australian species.