I think it sounds like an absurd proposition, but Federated Farmers (FF) and New Zealand’s conservation group Forest and Bird (F&B) announced this week—in all seriousness—their intended goal of creating a New Zealand free of predators (see here). This extraordinary initiative, first sounded by the Predator Free NZ Trust in 2013, is achievable, they claim, by completely eliminating all of the rats, stoats, ferrets, possums, and feral cats in the country. It certainly is an ambitious goal. Can it be done? And more importantly, SHOULD it be done?
New Zealand evolved without predatory mammals, and the first rats presumably didn’t arrive until the first Polynesian settlers did sometime in the 13th century (although radiocarbon dating of rat bones and paleontological examination of chewed seed hint they could have been here earlier, see here). European settlers brought a variety of familiar animals with them, and imported brushtailed possums from Australia to build a fur trade. Escapees soon inhabited New Zealand’s forests.
Today, the rats and stoats and possums and ferrets and wild domestic cats are all on the blacklist. While many farmers want to control bovine TB (rare in New Zealand, but not eradicated, and possums are carriers), conservationists argue that native birds-- 37 native New Zealand birds are classified as “threatened”—are at risk as long as predators roam the forests.
While pest trapping occurs in some areas, the various conservation departments and farming organisations tend to favour poisons for their pest control. The aerial use of highly-toxic 1080 is the most controversial of the poisons used, especially given the aerial method of application. New Zealand uses about 85% of the world’s supply of 1080, and rather than import it from the US, the West Coast Regional Council has invested in a 1080-manufacturing plant in Rolleston, an “innovative business decision”. This year (2014) has seen the most comprehensive coverage of New Zealand native forest with aerial drops of 1080 (see here) under a Department of Conservation campaign titled “Battle for Our Birds”, based on the argument that beech tree masting in 2014 will result in so much food that the forests will be over-run with rats, and when the seed runs out they'll turn to birds for food. (The fact that beech trees mast on a regular basis and this hasn't happened before appears irrelevant--but that's off the topic.)
Besides the absurdity of thinking all of the predatory animals in New Zealand can be eradicated, and the ridiculous amount of poison that would have to be dumped on the country to do that (presumably without endangering humans, pets, and livestock), there is a very real question here about the ecological value and benefit of removing predators from the environment. Indeed, the removal of predators from an ecological system almost always has detrimental effects.
Elsewhere in the world, ecologists are increasingly becoming aware of the important role predators play in maintaining a stable ecosystem and encouraging biodiversity. Whether talking about large predators such as wolves and lions or small predators such as sea stars or codfish or armadillos or spiders, the trophic cascade that develops when predators in the ecological system are removed has profound implications for the health of the other residents in that system, often putting the most vulnerable creatures—those most in need of protection—at even greater risk. (See Caroline Fraser’s The Crucial Role of Predators.)
There’s a great little you tube video that shows what happened when wolves were reintroduced into Yellowstone National Park in the US. The impact on, and enhancement of, the entire ecosystem was profound and surprising. The removal of such animals would undoubtedly have the reverse effect.
While rats and stoats may not be wolves, and conservationists might argue that New Zealand wildlife developed without mammalian predators and has no need for them, the fact remains that their removal would undoubtedly have profound and unexpected implications for our wild spaces now.
New Zealand is a unique island nation, but it is no longer isolated. Man has come here, with his cows and his sheep, his horses, and deer, and dogs, and cats. Early Maori exterminated the moa, large flightless birds that once browsed the forests, and used fire to turn thick forests into more amenable grasslands. Modern man has brought his crops of corn and wheat and ryegrass, his aeroplanes, his herbicides, and his pesticides to these island, and he has now decided that the wilds must not be allowed to develop naturally under the auspices of Mother Nature (who no doubt delights in having a good variety of plants and animals to play with), but that even the wild lands must be managed, just like any good farm.