02 July 2009

Positive Changes for Rat Island Following Rat Removal

Nesting by a variety of birds at Rat Island are "early signs" that the removal of unwanted Norway rats has made the Aleutian Island a more suitable place for the local avifauna.

"Early signs of positive ecosystem change were documented" during a recent visit by U.S. Fish and Wildlife Service officials and other partners involved with the project. "Nests and chicks of black oystercatchers, glaucous-winged gulls, and common eiders were observed, in addition to a first-time record of breeding seabirds on an offshore rock previously inhabited by rats."

"Reports from the camp indicate that all bird species on the island except eagles are present in numbers similar to those found during pre-treatment surveys, according to a press release. "Falcons and gulls were observed successfully nesting on the island, and several observations of live adult and sub-adult eagles were made.

"Species such as murrelets, storm-petrels and puffins are expected to eventually recolonize the island if the rat eradication was successful.

"No living rats have been detected on the island, and the Service and its partners are cautiously optimistic that all of the rodents have been eradicated. If another year passes without a rat sighting, the team can declare the island rat-free for the first time in 229 years" since the rats were introduced due to a shoreline shipwreck.

Rat Island was treated in the fall 2008 with a bait containing the brodifacoum to remove the introduced Norway rats.

"A survey team dispatched to the island this May encountered a higher-than-expected number of carcasses of two non-target species. Biologists found 213 glaucous-winged gulls and 43 bald eagles. The team of biologists has reported no evidence of ongoing mortality on the island.

"The U.S. Fish and Wildlife Service has received laboratory results on an initial group of bird carcasses collected on Rat Island in late May and early April. Examination of the livers of two bald eagles, two glaucous winged gulls, one peregrine falcon, and one rock sandpiper all tested positive for the rodenticide brodifacoum."

F.W.S. officials are "in the process of analyzing all of the viable bird remains and tissue samples collected, in order to more fully understand the cause of mortalities and more effectively plan future operations in the Aleutians. Results will be released when they are available. In addition, soil and water samples were collected, and will be analyzed to more fully understand the potential movement of the rodenticide into, and degradation from, the ecosystem.

"The Service has no evidence that new mortalities have occurred. The partnership intends to dispatch a second team in early August to continue monitoring on the island."

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