Invasive species often pose critical risks to native flora and fauna. Animals in New Zealand are particularly susceptible as they evolved in an environment without mammals (except for a couple of species of bat). Local bird and reptile populations were then devastated by rats that arrived with the Maori colonisation in the 13thcentury, and by stoats and possums that came with the European settlers. Risk mitigations, particularly environmental ones can sometimes have side effects or raise protests, and the benefits must then be weighed against the contraindications.
More than 800 native species have now been pushed to the brink of extinction as a result of these invasive species, so the New Zealand Department of Conservation (DOC) has been trying to save them by dropping pellets laced with 1080 (Sodium Fluoroacetate) from helicopters on to government-owned forests. 1080 is a highly effective poison that does not affect native species, and which biodegrades and therefore does not seep into the water supply. 1080 is particularly effective against possums which transmit bovine tuberculosis and of which there are around 30 million in NZ.
Despite the beginnings of recovery of bird populations, including the iconic kiwi, there have been widespread and sometimes violent protests against these actions. Hunters protest that deer may be killed, and some animal lovers object to the mass killing of any animal. Also, in spite of assurances, some people believe that the poison will get into the water supply (there has been water pollution from intensive dairy farming but not from 1080).
Protesters have sabotaged DOC vehicles and also threatened to put 1080 into baby milk formula on sale in supermarkets. Photos of dead kiwis have been circulated on social media but later proven that the kiwis had been killed by dogs. The issue now for the NZ government is whether the side-effects of the mitigation are worth the overall benefits of the scheme, or whether they should re-think the mitigation.
Sources: The Economist magazine, Wikipedia