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Rats on Alaska Islands

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Aleutian Islands

The central and western Aleutian Islands have been always isolated from the Alaska mainland since springing up from the ocean's floor 50 million years ago.This separation from the mainland has allowed seabirds to colonize islands in the absence of land-based predators. Some islands support an incredible abundance of a variety of seabirds that return to the seaside cliffs to nest and raise their young. Worldwide, more extinctions occur on islands than on the continents. The introduction of non-native vertebrate predators by an to islands has been the primary reason for the loss island biodiversity. Most of the Aleutian Islands are a part of the Alaska Maritime National Wildlife Refuge. Islands were set aside for the protection of seabird colonies and marine mammals. Former uses of refuge land included fox farming. Livestock were permitted on some islands, and reindeer were stocked on a few. Subsistence hunting occurs throughout the refuge.

Rats Invade

Over 150 years ago Japanese ships were designed, by order of the Emperor, to swamp if they ventured into large following seas and traders were banned from going abroad. About this time, a wrecked Japanese ship was noted on the shores of the recently discovered and relatively unexplored island in the Aleutians. The early Russian visitors to the island noted that, unlike other Aleutian Islands, this one was infested with rats. The island became known as Rat Island. Later, other islands in the chain became infested by norway rats during these wooden ship days.

Rats can colonize an island quickly because of abundant food such as nesting seabirds, absence of other mammal predators or competitors. Norway rats are especially adept at preying on upon a wide range of wildlife, especially along coasts and wetlands. Besides eggs, chicks and nesting seabirds, rats also eat leaves, stems, berries, insects, spiders and fish. Rat populations are able to survive on islands after the seabird migration because they can utilize a wide variety of foods.

A new wave of invasion of rats to the Aleutians came during WWII in ships and cargo of both American and Japanese troops. No one knows exactly when rats first came ashore to the outposts, but over seven large islands that had been rat-free before the war became infested during their occupation.

A Different KInd of Rat on Shemya Island Rats were first documented on Shemya Island, in the far western Aleutian chain, near the end of WWII. Since that time, Shemya was occupied as a US military Air Station. But two curious facts became apparent in 1995 after a visit by biologists: the rat population had apparently died out, and the species of rats was different than on other Aleutian Islands. Shemya had been invaded by roof rats (Rattus rattus).

Rat Studies in Bay of Islands and Kiska IslandDrawing on the success of other island managers, the refuge is experimenting with rat eradication starting with bait trials on small islets. Between 2002 and 2006 the refuge conducted studies on Adak islets and Kiska Island to better understand rat behavior, biology and eradication methods in the Aleutians. Other studies on Kiska focused on the last major seabird colony (least and crested auklets) existing on an Aleutian Island with rats. Here are some PHOTOS of Kiska Island.

Pribilof Rat Prevention Project North of the Aleutian chain lays two islands, known as the Pribilof Islands, that support the largest fur seal and sea lion rookeries in Alaska. They are also home to 2 million nesting seabirds 0f 12 different species. Both islands have been visited seasonally and later occupied by humans after their discovery in 1786. As demonstrated in the Aleutians and on islands worldwide, the likelihood of rat invasion to an island greatly increases after settlement by people. In the early 1980's the government addressed this threat by establishing a network of "rat houses" and boxes armed with traps and poison to intercept and kill invading rats.

Bait Trials in Bay of IslandsA bait trial concluded in October 2006 on a half-dozen islets around Adak Island was a step toward eradicating rats on a larger refuge island. The 2006 Bait Trial on islets with the Bay of Islands enabled the Service and partners The Nature Conservancy and Island Conservation to simulate helicopter broadcast of rodenticide on small islets and study risk to wildlife, and effectiveness of the rat bait in the Aleutian environment. Here are some PHOTOS from that study.

Rapid Response Planning for Shipwreck Rat Spills Rats were accidentally transported to more than a dozen large Aleutian Islands in ships and cargo brought ashore beginning in the Russian explorer days and throughout WWII. The first island known in the Alaska to be invaded by rats was from a Japanese shipwreck that washed ashore on an Aleutian Island about 1780 (Rat Island). Today the refuge is working to reduce the incident of rats on ships working in the Aleutians. They have also developed a strategy to combat rats coming ashore from a shipwreck with the use of traps and rodenticide.

Rat Island Eradication The proposed eradication of rats on Rat Island (6,871 acres). Rat Island could begin as early as October 2008. The purpose of the eradication is to restore native seabird nesting habitat by eliminating an invasive predator: Norway rats. The project is a partnership between the US Fish and Wildlife Service, The Nature Conservancy, and Island Conservation. Rat Island is being considered for the first island rat eradication project on the refuge because of its smaller size compared with other infested Aleutian Islands. Also, its remoteness and distance from other islands will reduce the likelihood of becoming re-invaded by rats hitchhiking on ships and floating debris. See PHOTOS from Rat Island taken June 2008.

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