Alaska's Rat Island is finally rat-free, 229 years after a Japanese shipwreck spilled rampaging rodents onto the remote Aleutian island, decimating the local bird population.

After dropping poison onto the island from helicopter-hoisted buckets for a week and a half last autumn, there are no signs of living rats and some birds have returned, according to the United States Fish and Wildlife Service.

Rats have ruled the island since 1780, when they jumped off a sinking Japanese ship and terrorised all but the largest birds on the island.

The incident introduced the non-native Norway rat, also known as the brown rat, to Alaska.

The $US2.5 million Rat Island eradication project, a joint effort between the US Government, the Nature Conservancy and Island Conservation, is one of the world's most ambitious attempts to remove destructive alien species from an island.

Now there are signs that several species of birds, including Aleutian cackling geese, ptarmigan, peregrine falcons and black oystercatchers, are starting to nest again on the 26 square kilometre island.

Fish and Wildlife Service spokesman Bruce Woods says they will officially be able to declare the island rat-free after two years of monitoring.

"We don't know that there's not a couple of happy rats hiding away that are going to spring out and repopulate the island," he said.

- Reuters