Talk to the Animals: 5 of NZ's worst animal invasions

Possums are perhaps the most infamous of all our invaders. Photo / File

Opinion

There are aliens living amongst us, not little green men but foreign animal species from ecosystems far away. These invaders have quite reasonably done what all animals will try to do - survive and reproduce. Some have thrived and in doing so have put significant pressure on New Zealand's native animals.

A natural ecosystem controls the numbers and spread of its individual species through a complex food web that keeps populations in check allowing each species to coexist without wiping each other out. In some cases, new organisms thrust into the mix will find themselves awash with food and other resources and in the absence of significant predation will begin to multiply exponentially. This is when the problems start.

Some of the most notable introductions to our own fragile ecosystem:

Possums

Resulting from a failed attempt at to start a fur industry in 1837, possums are perhaps the most infamous of all our invaders. With a population estimated in excess of 50 million, they are hard to miss, occupying farmland, forest and even suburban backyards. They are voracious feeders, stripping trees of leaves, fruit and flowers, destroying favoured species before moving on to the next, and in doing so taking food away from resident wildlife and altering the entire make-up of the forest. Possums don't stop at vegetation and will also prey upon birds, eggs and nestlings as well as lizards, frogs, bats, insects and other invertebrates.

Currently the only large scale means of effective possum control is the poison 1080.

Cats

Photo / File

The first cats to arrive in NZ would have jumped ship after being resident rat catchers aboard vessels visiting our shores from the end of the 18th century. About a century later when rabbits had caused some farmers to abandon their farms, cats were deliberately released in an attempt to control them. Forest birds where much preferred however and are easily caught by these skilled feline hunters. Cats are notoriously difficult to control.

Rats

The first rat to reach our shores was the diminutive Kiore which following its arrival with Polynesian explorers around 1250AD set about exterminating all Tuatara on the mainland. The Kiore has been largely displaced by the introduction of the Norway rat in the late eighteenth century and then the ship rat some time later. Rats are now found in most corners of the country and collectively have a massive impact on native wildlife. They are fairly indiscriminate feeders consuming not only any accessible wildlife but their food as well.

Stoats

Photo / File

In another ill conceived attempt to curb the spread of rabbits, a large consignment of stoats was imported from the UK in 1870. Preferring the more easily attainable birdlife, one of their most notable achievements was as a major contributor to the loss of the little spotted kiwi from the mainland. Stoats are a 'super hunter' able to climb, swim and burrow and multiply quickly in response to favourable conditions.

Humans

Around 75 per cent of NZ forests have been destroyed by people. These same people brought the foreign species mentioned plus many more to our shores, either by accident or deliberately. They hunted native species with seemingly no concern for taking every last one. I will never see a Moa or the enormous Haasts eagle that once preyed upon it. I will never hear the flute like call of the Huia or see the shiny blue fur of the Greater Short Tailed bat. I feel a very real loss as I look at their lifeless museum representatives and sadness at just how recent and preventable some of these extinctions were.

We have never known as much as we do now about the delicate balance that is nature. As the animal that has had by far the greatest effect on the extinction of our fellow species, will we listen to and act upon this knowledge to halt further reduction in the country's and indeed the planet's incredible biodiversity or will we just concern ourselves with what we can take while on our own short journey?