“The conservation decisions we make today will have repercussions for millions of years to come,” says Luis Valente of Museum für Naturkunde in Berlin and the paper’s lead author.

“Some people believe that if you leave nature alone it will quickly recuperate, but the reality is that, at least in New Zealand, nature would need several million years to recover from human actions — and perhaps will never really recover.”

While the number of lost or threatened bird species often has been quantified, the team explains, the broad-scale evolutionary consequences of human impact on island biodiversity rarely have been measured.

Valente says that the biodiversity levels observed today are the result of millions of years of evolutionary time, and that extinctions caused by humans erase this history. So, for their new study, the team developed a new method to estimate how long it would take for a particular closed ecosystem (i.e. island) to regain the species it lost to human activity.

New Zealand happened to be an ideal case to apply and demonstrate this new method, spawning the present study.

“The anthropogenic wave of extinction in New Zealand is very well documented, due to decades of paleontological and archaeological research,” Valente says.

“Also, previous studies have produced dozens of DNA sequences for extinct New Zealand birds, which were essential to build datasets needed to apply our method.”

The team used computer models to simulate a range of human-induced extinction scenarios and see how the ecosystem fared following these.  All in all, they report that it would take approximately 50 million years to recover the number of species lost since humans first arrived in New Zealand.

If all species currently under threat are allowed to go extinct, they add, it would require about 10 million years of evolutionary time to return to the numbers of species today. However, not all is lost.

“The conservation initiatives currently being undertaken in New Zealand are highly innovative and appear to be efficient and may yet prevent millions of years of evolution from further being lost,” Valente says.

In the future, the team plans to estimate evolutionary return times for several other islands worldwide and see if any risk losing more evolutionary time. They also want to find out which anthropogenic factors play the most significant role in determining those losses.

The paper “Deep Macroevolutionary Impact of Humans on New Zealand’s Unique Avifauna” has been published in the journal Current Biology.