If there are less possums in our forests, does that mean there will be more rats?

Many won’t be thinking about a question like this, but for third year University of Auckland PHD student Tess O’Malley (pictured), it is a topic she has been studying for over a year.

In February 2019, Tess set up two 2.5 hectare research sites on Egmont National Park to understand the speed of recovery bounce back of rat populations after an aerial 1080 operation.

One site is on the Kaitake Range, which has a very low possum population due to two 1080 prescriptions in 2019; and the other on the York Road-side of the Mounga which has a higher possum population. This site represents the whole Mt Taranaki and Pouakai Range which only had one 1080 prescription in 2019.

Each site contains 49 rat live cage traps, spaced in a grid formation. Wax tags to monitor possums in the area and sensor cameras to capture the movements of predators and birds are also set up.

Initial baseline results were gathered in early 2019, before the first 1080 operation across the park. She has since returned every three months to log results and reset survey the site.

Tess is enjoying the hands-on experience she has gained in this field work. In addition, she feels well supported and is learning a lot from Taranaki Mounga Innovation Lead Tim Sjoberg.

“The team is fantastic, very supportive and experienced,” says Tess. “Tim has also taught me a lot. Things like where to place traps and baits to get the best results. That type of knowledge you can only get with experience.”

With baseline data collection now complete, the recovery phase of research has started. Tess says this preliminary research has shown faster rat recovery in the Kaitake site than at York Road. However, it is still early days.

“It is yet to be seen whether this difference is due to lower Kaitake possum densities, or some other factor,” says Tess.

A clearer picture of which site has a quicker rat recovery and factors contributing to this will be known over the coming months. Tess will complete her PHD research in 2022.

Tim says having Tess conduct her field work on Egmont National Park has been hugely valuable.  It will help to understand what the level of rats populations after an aerial operation. Also, the recovery time of rats after an aerial operation before they are back to damaging levels, thereby impacting on our biodiversity.

“Rats have a big impact on biodiversity, and for our project this is important in our work to restore our Mounga,” says Tim. “Tess’ great work will help answer some critical questions and guide the timing and methods of future predator control operations.”