Today, mink are frequently found between the IX and XII regions. Of all the introduced species in Chile, mink is one of most detrimental to native fauna because it is a highly effective predator of species such as mice, terrestrial and aquatic birds, crustaceans and insects. However, it had been thought that mink were restricted to continental Chile, with no records of its occurrence in the southern archipelagos. However, in January and February 2004 an inventory of rodent populations was carried out on four islands of the Chonos Archipelago, region XI (Guamblin, Ipún, Stokes Island and Kent Island), during which evidence of invasion by the American mink was obtained.
For the survey we used cereal-baited Sherman traps both on the ground and in vegetation. No rodents were trapped on Ipún and Kent Island and few on Stokes Island, whereas rodents were readily trapped on Guamblin. The differences in trapping success could not be explained by methodology or any abiotic factor. On Guamblin, however, no signs of minks were detected whereas on the other islands droppings and tracks of mink were found and individuals were seen on several occasions. We believe that the absence or low numbers of rodents on the three islands are due to the impact of mink. Reports by fisherman on Ipún and Stokes Island indicate that rodents were abundant before the occurrence of mink.
Given the ability of mink to enter burrows of nesting birds and kill chicks and even adults, we are concerned that the population of diving petrels, shearwaters and other burrow-nesting bird species on the islands of the Chilean Archipelago could be severely affected by the mink. In addition, it is known that the mink is present on the Guaitecas Archipelago to the north of the Chonos Archipelago and close to Chiloé’s Island. This is of great concern as the Vulnerable marsupials Dromiciops gliroides and Rhyncholestes raphanurus and the endemic Darwin’s fox Pseudalopex fulvipes, with whom the mink could compete for food, occur on Chiloé’s Island.
The detrimental effects of mink on these Islands indicates the need for further research and monitoring of the fauna of the Patagonian Islands of Austral Chile to develop an inventory of species that may be threatened by introduction of the American mink.
Jorge A. Valenzuela & José H. Grau
Institute of Zoology, Universidad Austral de Chile