the stoats in the study ate surprisingly few birds. –Will Harvey, The Press, Monday 31 August 2020

Unexpected findings

By Roger Childs

Stoats are on the hit-list of the Predator-Free NZ movement and have been commonly blamed for killing myriads of birds. But a recent Department of Conservation (DOC) research study in three South Island National Parks – Nelson Lakes, Aspiring and Fiordland — has shown that they prefer small mammals, reptiles and insects. In many remote and high country areas stoats are also very useful in keeping rat numbers down and some conservationists see this as highly desirable. 

There are always consequences from targeting particular so-called pests. A few years ago in North Sydney foxes were targeted using 1080 poison. The result was a major increase in rabbits and bandicoot numbers in the residential areas. Sometimes it’s best to leave nature to balance things out.

Give stoats a break?

If only rats are taken out, stoats eat large quantities of native insects and lizards, an undesirable result.

There are plenty of sceptics on the logic behind the predator-free policy: for starters one public enemy — the possum — is not a predator. As it happens most birds are, especially the raptors like falcons and hawks.

Stoats are predators. However, according to DOC scientist, Jamie McAulay, they have a strong preference for ship rats. In the South Island survey of stoats there were no bird remains in the stomach contents of the Aspiring and Fiordland samples. Even in the Nelson Lakes where there are no rats, birds made up less than 2% of the stoat diet.  

The survey found that stoats have a “highly flexible” diet and like wetas and skinks. However the scientists involved in the sampling in the National Parks noted that much more information is needed.

Leave nature alone?

Rats have been in New Zealand for well over a thousand years and stoats for over 200. Most of the country’s birds have survived and those that didn’t like moa, Haast Eagles and huia were exterminated by humans, especially by the early Polynesian inhabitants and their predecessors. 

Realistically, rats, stoats, mice, ferrets and possums will still be here in another thousand years. As it always has, nature will sort out an equilibrium within the wider environment.