The Department of Conservation has confirmed that there is at least one stoat on Kapiti Island.
The island near Wellington was declared predator-free in 1998.
A contractor on the island reported seeing a stoat in November.
DoC now says a dead bird and stoat DNA in faecal matter confirm the presence of a stoat.
A mustelid detection dog and handler will spend the next two weeks on the island searching for more signs of stoats.
More faecal samples will be tested to determine whether there is more than one stoat present on the island.