This is a black petrel, a tākoketai - a seagull-sized bird that only nests in New Zealand.
Once found across the North Island and near Nelson, the species has dwindled to a colony of about 5000 breeding pairs here on Aotea/Great Barrier Island, and a smaller colony on Hauturu/Little Barrier Island.
For nearly 30 years now, a team of conservationists have surveyed the Aotea colony, precariously located on the summit of Hirakimata/Mt Hobson, the island's tallest mountain.
The birds of the colony are good breeders. On average, more than 70 percent of petrel parents monitored by the survey successfully fledge a chick each year.
But of the thousands of chicks that have been banded over the decades, only about 10 percent of them have ever been found again.
What happens to the rest is still largely a mystery.