This article is available in Spanish through a partnership with the Institute of Ecology at the National Autonomous University of Mexico. Read in Spanish >>
Over a century ago, New Zealand was faced with a very tiny, very adorable problem. As is the case for just about any island onto which our species has settled, we brought a menagerie with us. Rats and mice are now everywhere humans are, along with dogs and cats, but the main problem for New Zealand was bunnies. Rabbits were everywhere. At that time, the favorite method for dealing with an invasive pest like a rabbit was to introduce a predator known to have a predilection for gobbling up that invasive pest. That’s why, in 1884 and 1885, the government of New Zealand released at least 224 stoats from Great Britain.
Stoats (Mustela erminea) are mustelids, which means they’re related to animals like weasels, otters, badgers, ferrets, minks, and wolverines. On their native Great Britain, more than 80% of the stoats’ diet was made up of the European rabbits, and that’s despite the fact that the rabbits themselves are invasive in Britain. They were first brought to the British Isles some 2,000 years ago and became fully naturalized by the mid-12th century. So New Zealand’s plan was to round up a bunch of British stoats and hope that they could clean up the island’s rabbit problem…like a bunch of very cute municipal workers.
In the third year of New Zealand’s rabbit solution, another 3,000 stoats and weasels were sent from Lincolnshire alone (because historical records are vague, it isn’t clear how many of that 3,000 were stoats and how many were weasels; either way, it was a lot of each). Over the next 20 to 30 years, thousands more would be released; nobody quite knows how many. By the end of the 19th century, so many stoats had been released and in so many places that they’d completely colonized both of New Zealand’s main islands.
While New Zealand’s new stoats went about their business – chowing down on rabbits and making little stoats – their cousins back home in Britain would eventually face a problem of their own.
In the early 1950s, the myxoma virus began to appear in Britain. When the virus infects a rabbit, it causes a disease called myxomatosis, which is often just called “myxo.” The illness spreads among rabbits either through direct contact or indirectly, when bitten by a flea or mosquito that had previously fed on an infected individual. Infected rabbits usually die within two weeks, but not before developing skin tumors, blindness, fatigue, and fever.
Between 1953 and 1955, the illness wiped out nearly 99% of Britain’s rabbit population, with the support of a weary UK government, who knew the kind of havoc that the invasive rabbits could wreak on agriculture. In some places, the virus was intentionally introduced or spread as a means of pest control by placing sick rabbits into burrows with healthy ones.
But fewer rabbits meant less food for their predators, including stoats. Young stoats died of starvation, and fewer pregnant or nursing females were observed than in the years before the disease made its way through the rabbits. Though stoats did began to rely more heavily on invertebrates, birds, and rodents, that behavior change wasn’t enough to keep their numbers from crashing. The average number of stoats caught on game estates decreased by 84% each year for a decade following the outbreak.
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