Man’s worst friend
In a country where our most precious birds can’t get off the ground, it’s no wonder that we have become the rat’s worst enemy.
According to conservation biologist James Russell of Auckland University New Zealanders have been locked into a “co-evolutionary arms race” with rats since they first hitched a ride on European ships of the 18th and 19th centuries. “Humans are very good at survival and rats are one of a number of species that are good at surviving with us. Wherever we go, rats are soon to follow. As we develop new ways of being able to control rats they will evolve a way to avoid being controlled whether it be by behavior or genetic adaption.” It’s a struggle that has seen New Zealand become fully infested with, in particular, Rattus rattus or ‘Ship rat’ which according to Russell has now reached every area of available habitat in mainland New Zealand and lives in high densities except on those reserves and offshore islands where rats have been
33% of all global rat eradication programs have been run by us.
eradicated and excluded.
While rats may have pretty much over-run us we have responded by becoming world leaders in their management and eradication. ‘We are the best in the world. Pest control and other conservation techniques are the ‘silicon valley’ of our technological export,” says Russell – which sort of makes him the Steve Jobs of global rat control – with calls far and wide to advise and assist, including at an eco hotel on Marlon Brando’s private atoll in French Polynesia. Currently 33% of all global rat eradication programs have been run by Kiwis. In the 1990s it was more like 50% but as we export our knowledge so other countries become skilled at dealing with their own problems.
The pace at which rats can pro-create and cause devastation to native birds, insects and plants is astounding. In 1963 a couple of rats got out to Big South Cape Island – a mutton birding island of about 2000 hectares, just southwest of Stewart Island. Within one year rats were across the entire island but at a low density. Three years after first arriving they were across the entire island at high density, two species of bird and one species of bat were extinct and a number of other plants and invertebrates were also locally extinct.
We are talking here in particular about the Ship rat, the most damaging, pervasive and prevalent of the three species that inhabit New Zealand. The others are the Norway rat and the small remaining populations of Kiore or Pacific rat which, though considered a pest by DOC due to evidence of predation on native birds, lizards, plants and insects, have cultural significance for Maori, especially Ngati Wai, who see themselves as their guardians. What makes ship rats such a threat to New Zealand’s flora and fauna is their adaptability – or ‘plasticity’ as Russell calls it. “They are able to survive in the most extreme environments, on islands from the highest latitudes through to the tropics.” Rats are omnivorous and their diet mostly consists of 50% plants (fruit, seeds and seedlings) and 50% invertebrates. Birds, its surprising to find, are not often on the menu because of their comparative rareity. “Even though they have such a negative effect on our birds and lizards its very hard to find a rat that has eaten a bird or a lizard because it’s a very rare item for them – a bit like caviar to us. However, there are so few birds and so many rats that only a few of the rats need to take birds for this to have an impact.” The impact is still huge, according to figures from Landcare Research; in 2012 rats, stoats and possums accounted for some 26.5 million native bird deaths in New Zealand’s forests.
The ship rat has developed a habit here in New Zealand that is unique in all the world. Because there are no other mammals that might prey on or compete with them in our native forests this is where they have established their highest population densities with much lower concentrations in urban areas. The problem is apparently as bad as it can get and now it’s about “reclaiming the territory” according to Russell. Money has key part to play, DOC currently has funding that enables it to carry out pest management on a mere four per cent of New Zealand’s land mass. Whilst there have been major successes on offshore islands there is still a huge amount to do. As work turns towards populated islands such as Great Barrier Island
there are challenges other than funding that make things tricky. Its not that people are opposed to rat eradication but there are issues over the methods proposed. While traps are widely considered to be humane in that the kill is usually instant but there are growing questions over the humaneness of anti-coagulant toxins.
Many might think that the way in which we kill our pests is irrelevant to the task of controlling them. But for Stu Barr of Wellington based Good Nature it is an issue for us all. ‘‘We are world leaders and we should be seen to be managing pest species in a humane manner. It is important how we as humans treat the organisms within our environment.” Good Nature has developed a range of humane selfsetting traps that are currently being trialled by DOC in six large-scale sites around the country. “It doesn’t help us to simply demonise rats, they are doing what they do naturally and circumstances have brought them alongside us and this environment. It’s our decision that they should be controlled to protect other species. We aim for no suffering. Using those toxins you know there is a period of suffering between ingesting toxins and their death.”
A humane method of deterring rats from coming into your home can be found with the plug-in devices which they find unpleasant. A computer-generated signal is sent through the electric cables at varying intervals in the building causing the electromagnetic field to pulsate. The benefits of this is that also deters cochroaches.
In the end we must reclaim our unique environment while we still can and it would be prudent for this to be realised for what it is worth to us all. Just because many of us can’t see the rats in the trees after dark as they rob nests of millions of native birds doesn’t mean we should turn a blind eye. Controlling rats on our land and in our gardens has significance as so many of our inhabited areas are close to pristine native landscapes. Russell points out that we have an economic imperative to continue the work we do so well overseas here in New Zealand. “There are a lot of islands in the world in the middle of nowhere and we just happen to be one that has an amazing conservation reputation which sees tourists make 12 and 24 hour flights to come here. If we didn’t have that one edge then people would go to some
other island closer to home.”
Our native birds have little or no protection against rats.