Mustelids have never colonised Stewart Island/Rakiura, but feral cats were present. During a survey, it was apparent that cats killed kakapo at a rate of 56% per year. At this rate, the birds could not survive on the island and therefore an intensive cat control was introduced in 1982, after which no cat-killed kakapo were found. However, to ensure the survival of the remaining birds, scientists decided later that this population should be transferred to predator-free islands; this operation was carried out between 1982 and 1997.