More than 70 separate species have become extinct, reported Berlin's Natural History Museum, where one of the team members, Luis Valente, works.
Despite current conservation efforts, 30 further bird species are at risk of extinction. These include the kakapo, a large nocturnal and flightless parrot.
The ground-dwelling bird was almost wiped out a few years ago, as a result of threat from imported animals, such as rats, martens, ferrets and cats.
The absence of indigenous mammals on the islands, with the exception of bats, meant that the kakapo had no defence strategy against these animals, which raid its nests on the ground. Hunting and changed land use also contributed to their decline.
The team based its findings on the fossil record, using computer simulation to extrapolate their results. "If the species currently seen as endangered were also to die out, 10 million more years would be needed," the museum said.
As a result of its isolation, New Zealand is home to birdlife not seen elsewhere, including its national symbol, the nocturnal and flightless kiwi.
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