Glacier retreat on South Georgia and implications for the spread of rats

Using archival photography and satellite imagery, we have analysed the rates of advance or retreat of 103 coastal glaciers on South Georgia from the 1950s to the present. Ninety-seven percent of these glaciers have retreated over the period for which observations are available. The average rate of retreat has increased from 8 Ma-1 in the 1950s to 35 Ma-1 at present. The largest retreats have all taken place along the north-east coast, where retreat rates have increased to an average of 60 Ma-1 at present, but those on the south-west coast have also been steadily retreating since the 1950s. These data, along with environmental information about South Georgia, are included in a new Geographic Information System (GIS) of the island. By combining glacier change data with the present distribution of both endemic and invasive species we have identified areas where there is an increased risk of rat invasion to unoccupied coastal regions that are currently protected by glacial barriers. This risk has significant implications for the surrounding ecosystem, in particular depletion in numbers of important breeding populations of ground-nesting birds on the island.