In July, the New Zealand government announced its intention to eradicate all rats, stoats and possums from the entire country by 2050 to save native birds such as the kiwi. It’s an ambitious plan, perhaps impossible to pull off with the methods available today, but it’s a stark reminder that invasive alien species today constitute perhaps the greatest extinction threat to animal populations world-wide.

Birdlife International, a charity that works to save endangered birds, reckons that of the 140 bird species confirmed to...