Suddenly, through the forest of massive stalactites and slender banyan roots, there came a clicking sound.
"Ah," said Marshall Humphreys, who was showing us through the Anatakitaki Cave on the island of Atiu, "they're getting ready to have breakfast."
From the darkness of a cavern a small bird came swooping, followed by another, then another. As they entered the daylight the clicking changed into a melodious tweeting. But when they swerved back into blackness, the clicking resumed. "They use the clicks as a sort of sonar to navigate through the caverns," said Marshall.
The birds were the rare Atiu Swiftlets, or kopeka, found only in this cave and another smaller one in an inaccessible part of the island.