Five Te Papa staff recently joined Department of Conservation colleagues on a boat-based survey of islands in central and northern Fiordland. One of the species they were hoping to learn more about was the mysterious grey-backed storm petrel. Vertebrates curator Colin Miskelly explains why this tiny bird was on their radar, and what they found.
Te Papa and DOC staff have undertaken a series of expeditions since 2016, searching for and counting nesting seabirds on more than 200 islands throughout Fiordland. One of the species that we have focused on is New Zealand’s smallest seabird, the grey-backed storm petrel. They have never been found breeding anywhere near the New Zealand mainland, but we now have overwhelming evidence that they probably breed at scattered sites throughout Fiordland.
Shining a light
The technique we use when searching for these storm petrels is spotlighting at night. Many species of seabirds return to their breeding grounds under the cover of darkness. For largely unknown reasons, they are attracted to bright lights, particularly on dark and misty nights.
We encountered three grey-backed storm petrels in Dusky Sound in 2016, prompting us to prepare and publish a summary of at least 21 birds observed or collected in Fiordland between 1889 and 2016. We saw at least five more birds in Chalky and Preservation Inlets in 2017, including capturing a bird with a bare brood patch (this bare skin on the belly allows transfer of body heat to the egg, and is a sure sign that the bird is breeding).
A break in the sequence
A year later I chanced on the remains of a grey-backed storm petrel while walking the Routeburn Track (yes – I have a small issue with work-life balance!). However, we failed to see a single storm petrel during a survey of islands in Breaksea and Dusky Sounds in 2019 – the moon was full and skies were clear, making conditions hopeless for spotlighting.
We had high expectations of encountering storm petrels on our latest visit to Fiordland, as we were there during a dark moon phase. Our itinerary also had us covering a lot of ground, from Milford Sound south to Dagg Sound, about 120 km apart. However, what we found exceeded all expectations.
Storm petrels everywhere
We encountered grey-backed storm petrels at all six sites that we moored or anchored, including an astonishing seven birds at the entrance to Milford Sound (two captured, with another five visible at once). Storm petrels were present both near the open sea, and at the furthest inland where it is possible to travel by boat, at the head of Hall Arm, Doubtful Sound.
A sign from above
The most remarkable encounter occurred just before dawn on the final morning of the survey. We were anchored at the head of Hall Arm, 27 km from the sea over the mountain tops, and 40 km by water. I am an early riser, and was entering survey data into a spreadsheet in the dark. The door to the rear deck was open, and at 0535 h a storm petrel flew in – apparently attracted by the bright screen of my laptop. The first I knew was when the bird hit me in the chest!
Where do the storm petrels nest?
To add to the intrigue, the bird had a fully bare brood patch. The likely explanation is that it had just completed an incubation shift and had flown down from the surrounding mountains to sea level, before heading out to the outer coast before dawn. We suspect that storm petrels have survived in Fiordland by breeding on ledges on cliffs, inaccessible to rats and stoats. Our sightings suggest they are spread across the length and breadth of a vast landscape. But will anyone ever find a nest?