You may have noticed that I continue to mention these things called introduced mammalian predators or pests. I realise that I haven’t yet informed my readers of what these pests actually are, and why they are so damaging to New Zealand’s natural environment.
The Sub-Antarctic Islands have not come out unscathed by introduced predators. To date, the Department of Conservation has carried out two separate eradication programmes on both Campbell and Auckland Islands – the latter of which, was a complete success. The only remaining pest species are pigs, cats, and mice on Auckland Island, and mice on Antipodes Islands (which will hopefully change in the near future).
This long overdue blog post is about five of the ferocious and frustrating pest species that plague New Zealand in general.
Please note that this blog post includes videos that may disturb and that these five pests are not the only predators plaguing New Zealand.
1. The Rat
We often hear about ‘rats’ being a pest, but did you know that there are actually three species of rat threatening New Zealand’s wildlife?
The kiore (or Pacific rat) was introduced by early Maori settlers in the 10th century and both the ship rat (black rat) and Norway rat were introduced by early European settlers in the 17th century.
All three species negatively impact the environment by eating rare weta, frogs, snails, tuatara, lizards, insects, birds, as well as the fruits, flowers, and seeds of native plants. Of all the species, the Norway rat is the largest, followed by the ship rat and both are known to prey on birds eggs, chicks, and even in some cases – the adults. They’re very bad news for biodiversity.
2. The Rabbit
The rabbit was brought into New Zealand in the early 1830’s as a source of food and activity in the form of hunting. What early european settlers didn’t predict was how well these rabbits would do, and how busy future generations of farmers would be keeping plagues of them from destroying their pastures.
In New Zealand, there were many attempts to control the population that included introducing stoats, poison, digging out burrows, and even establishing a commercial industry exporting rabbit skins. While some of these methods have controlled rabbit populations, they are still widespread throughout New Zealand.
In the Southern Ocean, the rabbit is best known for eating out entire fields of mega-herbs on Macquarie Island, an Australian Sub-Antarctic Island. A number of attempts to eradicate them from the island have occurred over the past 5 – 10 years with the main challenge being the quick removal of carcasses that is required to prevent secondary poisoning of carrion eating species such as skuas.
3. The Stoat
Ironically, the stoat was introduced to New Zealand with the hopes that it would control the rabbit population. Although it is a natural predator-prey relationship in the northern hemisphere, it didn’t turn out so well in New Zealand as the stoats found other New Zealand wildlife easier to catch.
Stoats are most problematic following a beech mast, which involves a large number of beech trees in a forest releasing their seeds at the same time. Following these events, mice numbers increase drastically and in the years following a beech mast, stoat numbers soar as they are able to prey on mice. Once mice numbers have declined, however, the increased stoat population will prey on native birds and animals and can have incredibly negative effects on native population numbers.
4. The Mouse
On the mainland, mice are most often observed eating berries, seeds, and insects on the forest floor. Like the stoat, they are most abundant following a beech mast on the mainland of New Zealand. Luckily for the Sub-Antarctic Islands, there are no beech trees to fuel such plagues. But that doesn’t mean they are not a threat to species in the Sub-Antarctic.
On islands, mice are recorded to act more like rats, and will take larger prey, including bird eggs, chicks, and even adults. A recent video shows a group of mice literally eating an albatross chick alive in the nest, a time when it is most vulnerable to predation.
Once again, I have to mention the Million Dollar Mouse project that Gareth Morgan is currently running, which aims to raise enough funds to eradicate mice from the islands. I keep pushing this project because I believe in it, and it’s a great way to raise awareness for Aotearoa’s Sub-Antarctic Islands.
5. The Cat
I think people tend to forget that their pussy-cats are the perfect predators. Cats often hunt out of instinct, and wont always eat their kill. They’re more likely to kill for a challenge, rather than to survive.
One example of the damage that cats can have is seen in the story of the Steven’s Island Wren. The most common story is that the lighthouse keepers cat, named Mr. Tibbles, was responsible for the species’ extinction. Although possible, it is more likely that the species became extinct as a result of predation by feral cats in the winter of 1895, just 14 years after humans first settled on the island in 1881.
While the best way to control cats is to treat them like every other pest, it’s only natural for humans to keep pets and we tend to believe that cats are the perfect companion. There are a few things you can do to control your pussy-cat, however, that will benefit both your conscience and the natives around you:
Keep your cats inside at night, have them wear a bell if they are outside at any time, have your cat de-sexed to prevent them breeding with feral cats, never abandon a cat, and of course the most obvious – try to keep your cat well fed and watered so that it’s never required to hunt to survive.