While we are working to clear Antipodes Island of mice, I recently learnt that one of New Zealand’s most important Nature Reserves, Maud Island, has been invaded by mice. Maud Island is a 318 hectare island in the beautiful Marlborough Sounds of the South Island of New Zealand. In late October 2013 biosecurity surveillance on the island detected the presence of mice. Much like for any unanticipated invasion, an immediate full-scale response was launched, including traps, tracking tunnels, and rodent sniffing dogs. It was soon determined that the mice had launched a very successful invasion indeed, having colonised most of the island before being detected. Maud Island is home to many rare species, including the endemic Maud Island frog, and other species of reptiles and insects. The impact of this mouse invasion on these species would be devastating if nothing were done. However, to mitigate these effects DOC plans to temporarily remove the most vulnerable species, including frogs and striped gecko, to other island sanctuaries and into captivity. In the coming year we plan to study how any impacts may occur and also try to determine where these mice may have come from, prior to their eradication from Maud Island.
The invasion of Maud Island highlights the ongoing threat of rodent invasion to islands, especially those which have never had such introduced rodents previously, and become arks for protecting vulnerable biodiversity. Despite biosecurity procedures in place to prevent invasions and detect them early, any island can be at risk of rodent invasion, or re-invasion. Our previous work in New Zealand showed that the average time for rodents to re-invade an island in New Zealand after eradication was about ten years. Conservation managers must be in constant vigilance for invasion and use the latest technology available, such as pattern recognition biometric software to determine the species of invading rodent, so the response can be tailored specifically.
Mice can be more difficult to eradicate compared to rats. They exist at much higher densities and have a much higher tolerance to rat poison by body weight. These factors may contribute to the lower success rate of mouse eradications on islands around the world. Its therefore all the more important that we study introduced mouse populations on islands, such as on Antipodes Island, to ensure we can maximise the success rate of mouse eradications on islands where it is sorely needed, such as Gough Island where introduced mice are eating seabirds to extinction.