Twenty-four of 44 new Kaka nest boxes built over the winter have been ripped apart, he said, adding that the birds then gouged out chunks of wood with their strong beaks.
"It may be that the challenge of taking doors off nest boxes is the Kaka equivalent to the Rubik's Cube," said Robertson. "As far as I'm aware, this extent of destruction has never been observed."
Kaka are acutely threatened by loss of habitat, competition from introduced species, and predators like stoats, ferrets and wild cats. They disappeared from the capital Wellington in the late 19th century when forests were cleared for settlement.
After an absence of more than a century, Kaka parrots were reintroduced to the Karori Sanctuary in Wellington in 2002 with six captive-raised birds. Since then, sanctuary staff have counted more than 100 juvenile parrots.
The birds are highly intelligent and extremely resourceful, Robertson said.
"It's hard enough for human hands to get the doors off, so the fact that Kaka have done it with just a beak and claws is pretty impressive," he said.
Sanctuary staff said the destructive behavior was more widespread than last year, indicating it is being learned by young male birds and imitated.
