A hunt by Environment Southland (ES) to find an established population of mice on Stewart Island/Rakiura has turned up nothing.

The operation, expected to cost around $20,000 (excluding staff time), was initiated after images captured in 2023 by one of Predator Free Rakiura's cameras showed what appeared to be a mouse.

While pests including rats are present on Stewart Island/Rakiura, the island has no known population of mice.

A 2023 Predator Free Rakiura image that sparked an Environment Southland hunt for a mouse population on Stewart Island Rakiura. Photo: Supplied/Predator Free Rakiura/Manaaki Whenua.

ES biosecurity and biodiversity operations manager Ali Meade said 26 rats were trapped during the project, which began earlier this month (May).

Contractors set up bait stations, traps, and cameras at eight sites, which were monitored for two weeks before being removed.

“Most of the rats captured were kiore (Pacific rat)."

"Some of them are very small, and one was caught in a mouse trap."

"The images captured by Predator Free Rakiura in 2023 are likely to have been of a small kiore, not of a mouse,” Meade said.

While the ES survey results do not prove that mice weren’t present on Stewart Island Rakiura, the results are very encouraging, she said.

“It’s great that we don’t have evidence of an established population of mice, but we still need everyone to do their part in making sure they don’t accidentally take mice to Stewart Island Rakiura, as this could have terrible consequences for conservation efforts and most importantly, our taonga (treasured) species.”

Rodents, including mice, can have devastating impacts on New Zealand’s ecosystem and taonga species. Mice can form huge populations quickly, and have been known to eat bird chicks, especially those in ground nests. They compete with native birds by eating many of the same foods like seeds and invertebrates. When mice eat seeds they destroy them, whereas when birds eat fruits and seeds, the seeds usually survive through the digestive tract and are dispersed as a natural way for native trees to colonise new areas.

It’s vital that everyone travelling to Stewart Island Rakiura and its surrounding islands remains vigilant by thoroughly checking their gear for any unwanted stowaways, she said.