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Addressing the Invasive Rodent Problem in the Aluetians
Date Posted: March 31, 2004Norway rats (Rattus norvegicus) have become established on at least 14 islands greater than 1,000 acres and many smaller islands in the Alaska Maritime NWR. The first invasive rodent introduction in the Aleutians may have been from a shipwreck in 1780 on what is now called Rat Island. Establishment of rats on most other islands within the refuge may have occurred during World War II. Recent studies of auklets on Kiska Island in the Western Aleutians have documented significant adult, chick and egg mortality attributed to rats, and extremely low reproductive success by least auklets. While Kiska has received the most attention, it is likely that rats are having negative impacts on seabirds, as well as other vertebrates, plants and invertebrates on many, if not all, of these islands. Recent successful rat eradication efforts in other locations (including islands in Hawaii, California, British Columbia, and New Zealand) hold promise that whole-island rat eradication efforts may also be feasible in Alaska. In 2003, the Environmental Contaminants program assisted the Alaska Maritime NWR with permitting for initial studies involving limited use of a rodenticide containing the active ingredient diphacinone in the Aleutian Islands. The immediate objective of this project is to investigate various issues related to the use of diphacinone at sites in the Aleutians, such as application rates, efficacy and potential non-target hazards. Removing Norway rats from selected small islands in the Bay of Islands, Adak Island will also have an immediate conservation benefit for the native ecosystems of these islands. Work completed in 2003 included pre-project bird surveys, pre-project studies of the intertidal zone, and deployment of the toxicant in bait stations on three small islets totaling 84 acres. No nontarget mortality was observed throughout the deployment period and the bait was highly effective. The Refuge hosted a workshop of experts in March 2004, including participants from New Zealand, British Columbia, Hawaii, California and Colorado, and Alaska. This group helped the refuge evaluate methods of removing invasive rodents from islands in the Aleutians and reviewed a near-term program strategy. One recommendation from the experts was that pilot studies such as the work in the Bay of Islands (which will continue in 2004) are needed prior to any larger scale efforts. The Environmental Contaminants program will continue to provide technical assistance to the Refuge throughout this project.