16 June 2009

Apparent Success for Rat Eradication at Aleutian Island

After a thorough survey of Rat Island, officials have found no sign of the Norway rats that had been present since they were introduced about 1780 when a Japanese ship wrecked on the beach, and the rats invaded.

"So far, no living rats have been observed," said Bruce Woods of the U.S. Fish and Wildlife Service, noting that seven observers walked the island looking for any indication of surviving rats. "We’re cautiously optimistic, but it’s a big island. It would be presumptuous to assume that we would have noticed rats if only a few were left."

A monitoring camp was established by biologists at the island on May 26, with results of the surveys reported June 10.

During the survey, several bird species, including Aleutian Cackling Geese, ptarmigan, Peregrine Falcons, and Black Oystercatchers were observed nesting on the ten-square-mile island.

The island will be surveyed again next year, before it is considered rat-free.

The goal was to restore the populations of seabirds and other parts of the native ecosystem.

"Restoring the natural habitat will likely bring back Tufted Puffins, Storm Petrels, Song Sparrows, Glaucous-Winged Gulls, Ancient Murrelets, and so many other important breeding seabirds," according to project sponsors. "Overall, the project will benefit at least 26 species of breeding birds, including at least 13 seabird species, some of which currently breed in small numbers on Rat Island or are restricted to breeding on small offshore islets."

Rat Island – comprising 6,861 acres is not inhabited and is located in the Aleutian Island Chain about 1,300 miles west of Anchorage, Alaska - is part of Alaska Maritime National Wildlife Refuge. It was treated in September 2008 when helicopters dropped 100,000 pounds of poison bait to eliminate the invasive rats, which preyed on bird eggs, chicks and small adult birds.

The island received its name due to its population of the rodents (Rattus norvegicus).

The visiting biologists also found "157 juvenile and 29 adult glaucous-winged gull carcasses and a total of 41 Bald Eagle carcasses that appear to have died in recent months. Seventy-five percent of the eagle carcasses appear to be juvenile birds."

The specific cause of death for these birds was not known.

"Several of the gull carcasses found initially are now at the National Wildlife Health Center’s laboratory in Madison, Wisconsin, and it is estimated that information on the cause of death will be available by late June," according to project officials. "Eagle carcasses and tissue samples were picked up from Rat Island by the refuge ship Tiglax on June 10 and will be shipped to the Wildlife Health lab after the ship makes port at Adak on June 11.

"Field personnel are in the process of collecting additional tissue samples for study before destroying any remaining bird carcasses to eliminate any possibility of ongoing risk. Reports from the camp indicate that all bird species on the island except eagles are present in equal or greater numbers than were counted during pre-treatment surveys. Although adult and juvenile eagles are still present on the island, numbers of sub-adult eagles are lower than pre-treatment totals."

None of the bird deaths happened recently, and Fish and Wildlife Service officials pointed out the losses "will not significantly impact" overall Aleutian bird populations. The agency estimates some 2,500 eagles live in the Aleutians, with gull numbers far higher.

In early May, a Partners in Conservation Award was presented to Rat Island Restoration Project, by Ken Salazar, Secretary of the Department of Interior, for this eradication effort.

The $2.5 million Rat Island Restoration Project, a partnership among the U.S. Fish and Wildlife Service, the Nature Conservancy, and Island Conservation, began operations in 2008 after a two-year planning process. This included an environmental analysis by federal regulators, who issued a Finding of No Significant Impact on April 15, 2008.

"Rat Island is the third largest of 250 islands world-wide where rats have been eradicated," according to F.W.S. officials. 

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