Estimated Impact of feral house mice on sub-Antarctic invertebrates at Marion Island

Abstract

The energy metabolism of feral house mice Mus musculus was established on sub-Antarctic Marion Island, using the doubly-labelled water turnover technique. Mean water influx was 565 ml kg-1 day-1 and mean CO2 production was 5.41 ml g-1 h-1, i.e. 3375 kJ kg-1 day-1. From the energy content of the main items (Lepidoptera larvae, Curculionidae) in the diet of the mice it was estimated that the dry mass of food consumed was 3.5 g mouse-1 day-1. The overall impact of mice on invertebrates, based on mean mouse density and the mean percentage invertebrates in the diet, was estimated at 108 g ha-1 day-1 or 39.4 kg ha-1 y-1 (dry mass). Greatest predation pressure was on larvae of the flightless moth Pringleophaga marioni: 65 g ha-1 day-1 or 23.7 kg ha-1 y-1. Insect biomass is lower on Marion Island than on nearby Prince Edward Island, which is mouse-free. It is suggested that populations of certain insects on Marion Island are depressed by the alien mice.