By Shawn Perich
You may not know what a stoat is, even though some are likely living near you. If you saw one, you’d say, “That’s a weasel,” which it is. The little predator we know as the short-tailed weasel is native across the Northern Hemisphere, including North America and Eurasia. Across the Pond, they call them stoats.
Whether you call it a weasel or a stoat, the critter’s winter pelt—pure white with a black-tipped tail—is known as ermine and is crafted into luxury clothing items. What I know about weasels is mostly what I learned from trapping them as a kid. My childhood traplines consisted mostly of rabbit snares, but I always had a couple of rat traps (supersized mouse traps), nailed to trees about a foot of the ground and baited with frozen meat. I’d catch a weasel or two every winter and always considered them a prize.
A creature that was a prize to me is considered a pain somewhere else in the world. According to Wikipedia, stoats were named one of the world’s top 100 “worst invasive species” by the International Union for the Conservation of Nature’s Invasive Species Specialist Group. Although they weigh just a few ounces, weasels are ferocious predators capable of wreaking havoc among native species in places where they have been introduced.
New Zealand is one place where stoats are raising Cain. Their introduction to island nation in the 1880s was a classic example of one bad idea following another. First, European settlers introduced rabbits to the island as a food source and reminder of home. The prolific rabbits soon became agricultural pests, which led settlers to introduce a familiar predator, the stoat, even though New Zealand and British scientists warned that doing so would likely have devastating consequences for native bird life.
And surprise, surprise—the scientists were right. New Zealand’s native wildlife developed in isolation, which meant the only mammals there when Europeans arrived were bats. With the absence of four-legged predators, many bird species were flightless. They proved to be easy prey for not only stoats, but also for introduced ferrets, ship and Norway rats, and feral cats that gobbled up native insects and amphibians, too. Now that the predator invasion has been underway for more than a century, the devastation of native wildlife has reached crisis levels. Roughly one-quarter of New Zealand’s native birds are already extinct. If iconic New Zealand species such as the kiwi are to survive in the wild, the non-native predators must be eliminated.
This morbid task was the subject of a recent story in The New Yorker titled “The Big Kill” by Elizabeth Kolbert, who reports that killing predators has become a national conservation campaign. Beginning with small offshore islands, New Zealanders have honed their predator-ridding skills. They have now eliminated predators from 117 islands, the largest being the size of Nantucket, as well as some fenced enclosures.
Killing predators isn’t pretty. The New Zealanders use some tactics long frowned upon in the U.S., such as aerial drops of the poison 1080. In fact, New Zealand accounts for 80 percent of the 1080 used in the world today. Rats, stoats and cats are trapped extensively by landowners and folks who consider themselves conservationists, and by schoolchildren. Apparently, the average New Zealander isn’t squeamish about predator control or trying to champion the rights of rats or feral cats. Kolbert reports a recent blog post about domestic cat predation was titled, “Mrs. Tiggy Winkle—Serial Killer.”
Now the nation is entering a new phase of predator control. In 2012, a prominent New Zealand scientist who was dying of cancer, Paul Callaghan, gave a speech where he proposed eliminating all predators from the nation’s mainland. As anyone who has ever tried to pull all of the weeds from a small garden or rid a hunting shack of mice before the deer season already knows, Callaghan’s proposal is a task of herculean proportion. It’s nearly impossible to get every last mouse out of the shack or weed from the garden. How would you ever get rid of millions of rats, cats, stoats and mice from an entire nation?
Kolbert reports New Zealanders seem up to the task. She talked with one predator control expert who said that even though the scale of the project is daunting, New Zealand has already made tremendous progress in scaling up its control operations. She also notes that predator control is a popular grassroots conservation effort that already takes place at a neighborhood or farm level. The goal, creating a predator-free environment for the restoration of native birds, has broad appeal.
New Zealanders are at the cutting edge of predator control technology. Kolbert visited a company that is producing a new, CO2-powered self-reloading rat and stoat trap that uses a spring-loaded piston to kill about 24 critters with one CO2 cartridge. A larger trap, designed to kill another introduced pest, the common brushtail possum, fills the critter’s skull with CO2 and emulsifies its brain. The self-reloader can take out 12 possums per cartridge. Deploy a few of these traps around the farm or in suburban backyards and you just might make a dent in the rat population.
New Zealand may never reach its goal of exterminating all of its invasive predators, but you have to admire the country for giving it a try. And maybe it’s possible. New Zealand’s North and South islands are relatively small and isolated. Having a relatively small human population of 4.4 million may make it easier to rally folks around a common cause.
Even if they are successful, a basic truth remains. It is easier to take measures—like rules and regulations—to prevent invasions of unwanted species than to attempt exterminating them after they arrive. New Zealander’s troubles with invasive species are entirely of their own doing. If they had listened to those scientists in the 1880s who said introducing stoats was a bad idea, they wouldn’t be struggling to get rid them and save their native birds today.