British Government-backed conservationists are launching an operation to wipe out rats on Henderson Island in the Pitcairn group.
The Henderson Island Petrel will become extinct within decades unless action is taken at the remote, uninhabited World Heritage site.
MV Aquila sets sail from Seattle this week, carrying two helicopters which will drop poison bait across the island, using methods developed in New Zealand.
Jonathan Hall, the project coordinator, says the island is home to more than ten globally threatened species.
"The Henderson Petrel is found only on Henderson, and it is one of the four petrel species that breed on the island. And really they underpin the island's ecosytem, bringing in a lot of marine nutrients on to the land, which they then deposit in their faeces. And that really is one of the main nutrient sources for the island."
Jonathan Hall says about 25,000, or 95 percent, of the endangered petrel chicks are eaten by rats every year.
The expedition will also undertake work in the Phoenix Islands and at Palmyra Atoll.