Concern an invasion of rats on Ulva Island, in Stewart Island's Paterson Inlet, could threaten its endangered bird population has led the Department of Conservation to ask boat users to check their vessels before visiting the protected sanctuary.
Four rats were recently caught in traps on the island, which had been rat free for 10 years and was home to mohua (yellowhead) and tieke (saddleback).
Biodiversity manager Brent Beaven said they suspected most rats got to the island, which is open to the public, by hitching a ride on boats.
"We will be working hard to make sure that we get rid of every last rat off Ulva Island before they can affect the bird populations."
However, people needed to check their gear and boats for rats, as well as weed seeds and mice.
