Ashley Bryan

Rodents In New Zealand: How Big A Pest Are They?

Currently, New Zealand is home to three invasive species of rat. These species include the Pacific rat which arrived from Polynesia around the 12th century, the ship rat which arrived near the end of the 1700s and the Norway rat which can be traced back to about 1860. All of these rat species prey on native lizards, insects and birds and are said to be responsible for a notable decline and relevant extinction of many native species.

History of Rat Infestation

Up until the 13th century, New Zealand’s only land mammals were bats. The native birds had nothing to fear from predators and became extremely docile. Many of these native bird species lost their flight abilities including the kiwi and the kakapo parrot. Since these birds are so gentle and grounded, they became easy prey for possums, weasels, cats, dogs and rats. In fact, more than 25 million eggs and chicks succumb to predators annually, nearly driving one quarter of the nation’s bird population to extinction. Many species of birds only live on islands where rats have been successfully eradicated or in small mainland sites where they are protected within predator-proof enclosures. This leaves hope for the time when these species can be released back into their natural environment where they will not be preyed upon.

2018 has been a long and hot record-breaking summer that has led to a massive explosion of the rodent population in New Zealand. The urban areas of the country have been hit the hardest with this population explosion. Rat and mice numbers have surged exponentially with ideal conditions for breeding and next to no natural predators to check their population numbers.

New Zealand has made a commitment to become predator-free by the year 2050 by exterminating all rodents and other invasive species including mice, rats, stoats and possums. If the pest elimination campaign is successful, New Zealand would be the first country in the world to be totally pest-free. The budget for this campaign will be enormous but it is completely necessary to check the population explosion, control it and eliminate the problem.

Global Warming Playing a Part

Global warming creates a double threat to this goal. This is because cities are host to high rodent populations and those rodents are moving to alpine environments which have always been free of pests. These alpine environments are a refuge for most of the endangered birds in the country. Entire bird populations have been totally wiped out when rat numbers are high and the worst of this will potentially occur in the spring when birds begin nesting. In fact, the New Zealand government says that introduced pest species will kill 25 million native New Zealand birds per year. The national bird of New Zealand, the kiwi, is dying at the rate of 20 per week and currently the population is less than 70,000.

Shockingly, the Norway rat is large enough to kill a seabird and a breeding pair can produce up to 22 babies in a single litter. A single breeding pair of rats can produce up to 2,000 offspring in a single year. In 2000 there was a severe rodent population explosion when there were two seed falls in the beech forest of the South Island. Many native bird species were wiped out in those areas and this has severely hampered the conservation effort surrounding rare birds including the orange-fronted parakeet for many decades into the future.

Eliminating the Problem of Pests

New Zealand’s existing rat control methods include dropping over 1,000 poison packets, ground baiting and trapping and ground hunting of possum. These methods have been extremely effective but have not completely eliminated the problem of pests. Currently, possum fur has become a growing industry and has been used to create winter clothing, so this provides incentive for hunters to supply the industry that creates this clothing.

If unchecked, the rodent population could quickly spiral out of control and New Zealand’s long-term goal of becoming pest free by 2050. To date, Australia’s Macquarie Island has been clear of rats although it is only 50 square miles in size and New Zealand is 2,000 times larger than that. The most important aspect of this is to have all residents on board and working together towards eradication. If just one pair of breeding rats escapes extermination they can quickly repopulate the area within six months.

An island’s rat population can also be exterminated by spreading genes through the wild population that make it super difficult for these animals to reproduce. This technique allows scientists to edit genes easily with great precision. Some scientists believe that there is the potential for ecological disaster if one nation’s good intentions were to spread throughout the world.

Unchecked, rodents continue to kill most native birds, but the benefits of complete eradication are numerous. The cost of the scheme which could span 40 years could cost as much as 9 billion NZD. Rodents were not native to New Zealand and continue to reproduce exponentially. Every homeowner can do their share by trapping and killing rodents in and around their own properties. Another important note is to keep attractants contained including garbage and seed from birdfeeders. Rodents are complete opportunists and will take the easy path to food if and when they can find it. Securing your home and property is another big step including sealing up areas that rodents could use to nest and rear young.

Restoration of Environment

New Zealand has created an intensive pest control plan which will see rats completely wiped out from the country within the next forty years. As lofty as a goal as that is, it is something that must be done to preserve the native wildlife and restore natural environments to the animals that rightfully should inhabit them. New Zealand needs to restore their country to the pest free status it enjoyed hundreds of years ago when Kiwi birds were able to roam without fear of being eaten by a predator.

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