Matt Rayner stands over a burrow, making a "waa-waa" noise.
The seabird scientist lingers a moment.
"No one home," he concludes, and pushes through tangled buffalo grass towards another group of slender rods marked with coloured tape. The rods locate burrows concealed by the grass.
Rayner repeats his call, tapping his fingers on his lips. This time he gets a reply, though it is audible only to his trained ear. He stoops and parts the thick shrub that offers perfect cover for the shy creature he wants to find.
Stretching into a burrow, Rayner, a University of Auckland seabird biologist, emerges with a scrappy grey-faced petrel.
"Careful," he warns the photographer, who bends close to the down-covered chick, "she may throw up on you." Too late. A thin jet of fishy fluid squirts from its mouth. Rayner calls it a "sardine smoothie ", a sign the juvenile is unhappy to be hauled from its home on Burgess Island, a rugged volcanic lump on the outer edge of the Hauraki Gulf, a place of remote beauty and intense avian life.
Rayner is among a small group of scientists and volunteers shedding light on the lives of the millions of Gulf seabirds.
Think New Zealand birds and kiwi, kakapo, tuis and kaka spring to mind. All are mainland birds. But offshore, tenuously tied to windswept, storm-tossed and often uninhabited islands, lives a seabird community more diverse than anywhere on the planet.
Of the 300 kinds of seabirds, 10 per cent breed only in New Zealand. The Gulf is a hotspot: even though they decamp for part of the year to places as far away as Ecuador and the North Pacific, Buller's shearwaters, black petrels and Pycroft's petrels breed nowhere else in the world.
The Gulf birds survive and prosper in the absence of predators and because food - plankton, tiny marine scraps, small fish - is abundant.
Yet despite their proximity to Auckland little is known about these curious creatures. What they have in common are characteristics adapted to life at sea.
One group are called tubenose birds, after a Nasal feature which helps them get rid of seasalt and detects telltale scents carried on seabreezes.
Adults spend their life on the ocean, and will fly vast distances to forage for high quality infant formula. The selfless sooty shearwater heads south as far as the Antarctic ice edge where it gorges in icy waters before returningwith a belly full of nutrients for its young.
Other species dance across smooth waves on delicate webbed feet - a spectacle which has earned petrels the name "Jesus birds".
The New Zealand storm petrel was thought extinct until 2003 when it was photographed off Coromandel Peninsula. Since then a handful have been captured and their identity confirmed by comparing DNA fragments with museum specimens held in Europe since the 1800s. Yet almost a decade since its rediscovery, scientists still do not know where this critically endangered bird breeds.
About the size of a thrush , the little bird is a holy grail for seabird investigators. For if its breeding sites can be located, scientists can decide how best to guarantee its future.
One clue which led to much head-scratching and meticulous research was a photograph taken by Neil Fitzgerald on January 8 last year of a New Zealand storm petrel with a stalk caught on its right leg.
From this scrap of evidence, and from getting up close and personal with the birds caught since the 2003 eureka moment, scientists have concluded that the hideaway of the hard-to-find petrels is on at least one of the rat-free northern Gulf islands.
Biologist Chris Gaskin says that small petrels, like storm petrels, are extremely vulnerable to predators.
"Until we find their breeding site," Gaskin says, "we must consider them at risk. If we can narrow it down to an island we know what risks they face."
Last month the Herald accompanied Gaskin and a group of seabird experts to Burgess Island, a three-hour trip out of Leigh on the launch Minerva II.
The group use a lighthouse hut on Burgess as a research base. Work includes studying the breeding biology of white-faced storm petrels, a Master's project for Massey University student Megan Young.
The team will fit electronic tags on birds to track them,monitor breeding and check for colony changes. This allows team members to fully test radio telemetry equipment that will be deployed on New Zealand storm petrels, birds caught at sea using a locally-developed net gun.
Gaskin, Rayner and others have funding from Birdlife International Community Conservation Fund and the Hauraki Gulf Forum to capture New Zealand storm petrels.
Gaskin is also trying another innovation in the great petrel hunt. He is working his way through hundreds of hours of calls collected by remote island recorders, analysing distinctive acoustic signatures of seabirds in the hope he can detect noctural chatter that could only come from the New Zealand storm petrel.
On the return voyage the boat stopped while a pack of fish remains was tossed overboard to attract the acutely sensitive seabirds.
It took barely 10 minutes for Cook's petrels, black petrels, fairy prions and flesh-footed shearwaters to appear at the stern of the Minerva - but not a single New Zealand storm petrel. Back from the dead it may be, but the little seabird remains as elusive as ever.