 <unk> 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 . 
