Is it ethical to kill millions of invasive predators in order to give native species a chance to survive?

This has been the quandary facing wildlife experts in New Zealand, which has adopted an ambitious goal of completely eradicating invasive predators from the island nation by 2050, according to NPR.

With beloved and iconic species such as the kiwi on pace to go extinct within a couple of generations, New Zealanders have had to decide which species will survive and which will die.

"If we don't take action, we are killing native wildlife by omission," explained Brent Beaven, manager of the Predator Free 2050 program at New Zealand's Department of Conservation, per NPR. "Choosing not to take action is an action. So either way, something's going to die based on the decisions we make."

The starkness of this choice has been playing out in New Zealand's efforts to completely eradicate the invasive stoat, which is a land mammal related to weasels and ferrets.

Stoats were introduced to New Zealand in the 1800s by European settlers, who had hoped that stoats would help control the population of rabbits, which were also an invasive species brought by outsiders, according to NPR.

The situation has highlighted the ethical and logistical complexity of protecting native ecosystems in a world so heavily influenced by human activity, with the circumstances playing out like a real-world version of the old nursery rhyme about the "old lady who swallowed the spider to catch the fly."

New Zealand wildlife has been especially vulnerable to the impacts of invasive species because native plants and animals evolved in relative isolation from so many of the predators present in the rest of the world.

For a long time, New Zealand did not have any land mammals besides bats, so species like the flightless kiwi never developed defenses against predators such as the stoat, according to NPR.

Now, in order to save New Zealand's native birds, wildlife experts have focused on removing these invasive predators from the ecosystem, which means killing millions of animals. While this might cause an ethical dilemma for some animal lovers, the solution to the dwindling kiwi population is clear for New Zealanders.

"The ethical questions that arise are really less about, 'Is it OK to do this?' and more about, 'What values should we be upholding as we do it?'" Emily Parke of the University of Auckland explained to NPR. "Even if we all agree with the aim of a predator-free New Zealand, we might disagree about ways of achieving that aim."

When it comes to the stoat, experts have found that the more progress they make, the more challenging the work becomes.

"They are very smart," said Claire Travers of the Whakatane Kiwi Trust, per NPR. "Very, very smart. I mean, a stoat can climb really well, get through very small holes, will take on a predator that's much, much bigger than it is."

Further, after two decades of eradication efforts, the stoats that remain are particularly difficult to catch, as they are the ones most able to avoid the traps used to kill them. They can even teach their evasive tricks to offspring, NPR reported.

The whole situation has served as a reminder of the incredibly devastating impact that invasive species have on native species and habitats. Invasive species often outcompete native plants and animals, disrupting the delicate balance of native ecosystems.

In addition to threatening native species with extinction, invasive species spread deadly diseases, destroy crops, and disrupt vital trade.