Half of New Zealand's native birds have gone extinct since humans arrived on the land and researchers have found it would take 50 million years to get them all back.
That's longer than humans have been on Earth. Humans in our modern form have existed for roughly 300,000 years.
Scientists from Massey University, and Berlin's Natural History Museum used computers to simulate various human-induced extinction scenarios.
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They found if all species of bird currently under threat were allowed to go extinct, it would take 50 million years to return to the same number we have today.
"Some people believe that if you leave nature alone it will quickly recuperate, but the reality is, at least in New Zealand, nature would need several million years to recover from human action," said Luis Valente from Berlin's Natural History Museum.
"Perhaps [it] will never really recover," he said on Tuesday.
He says the researchers will now use the same technique to estimate recovery times for other islands.
Although New Zealand has lost half its birds, the work we are doing now could prevent further tragedy.
"The conservation initiatives currently being undertaken in New Zealand are highly innovative and appear to be efficient," said Valente.
"[They] may yet prevent millions of years of evolution from further being lost."