Mice menace Antipodes fauna

Forest and Bird, Issue 282, 1 November 1996, Page 5

Mice menace Antipodes fauna

Lincoln University

John Marris,

AN ALARMING insight into the impact of mice on Antipodes Island, in the New Zealand subantarctic, has come from the first entomological collections on nearby Bollons Island. A recent Department of Conservation expedition to the Antipodes group provided the opportunity to compare the composition and abundance w

of the insect fauna between mouse-free Bollons and the mouse-infested Antipodes Island. The differences were dramatic. Counts of the larger species of beetles — thought to be highly vulnerable to mouse predation — showed numbers were much greater on Bollons Island. An example was the darkling beetle, Pseudhelops clandestinus, which was found to be common on Bollons Island while only a few specimens on a single rock outcrop have ever been found on Antipodes Island. In other instances, more specimens from a wide range of larger beetle species were found during the half-day visit to Bollons than were found in more than three weeks work on Antipodes. Mouse predation has probably caused the extinction of some insect species on Antipodes Island. A large, undescribed species of ground beetle belonging to the genus Loxomerus has not been seen since a 1969 expedition to Antipodes — and only then from fragments of a few specimens. Similarly, a species of weta is known from Bollons but no specimens have ever been collected from Antipodes. Questions remain about the wider effects of the reduction in insect numbers and loss of species through mouse predation. A study of the impact of mice on Marion Island in the southern Indian Ocean showed that the reduction in numbers

of a litter-feeding caterpillar by mouse predation had a marked detrimental effect on nutrient recycling on the island. A similar scenario could be true for Antipodes Island. Time is running out for Pseudhelops and species like it on Antipodes Island. DoC has identified mouse eradication as a management priority for the Antipodes group but, at around 2,000 hectares, the main island represents a significantly greater challenge than any previously attempted mouse eradication. However, rapid improvements in rodent eradication technology give some hope that mice will one day be removed from Antipodes Island. In the meantime we can be grateful for the insight that unmodified islands, such as Bollons, give to the conservation needs of our often neglected insect fauna.