From the wikipedia entry:
There had been a long-running controversy about whether the Kea preys on sheep, with the earliest reports appearing in 1867. An article by naturalist G.R. Marriner in 1906, describing substantial anecdotal evidence of these attacks, became the accepted view of the bird's habits. Several prominent members of the scientific community concluded that the rumours were true, although others were not convinced. However, in 1962 animal specialist J.R. Jackson concluded that the bird may attack sick or injured sheep, especially if it mistook them for dead, but that it was not a significant predator. Finally, in 1993, its nocturnal assaults were captured on video,, proving that at least some Kea will attack and feed on healthy sheep. The video confirmed what many scientists had long suspected, that the Kea uses its powerful curved beak and claws to rip through the layer of wool and eat the fat from the back of the animal. Though the Kea does not directly kill the sheep, death can result from blood poisoning or accidents suffered by animals trying to escape.