Little bird, big country: searching for nesting storm petrels in Fiordland

Little bird, big country: searching for nesting storm petrels in Fiordland

Te Papa bird curator Colin Miskelly describes a recent (pre-COVID lockdown!) attempt to solve a mystery that he has pursued in several remote parts of Fiordland over the past four years.

The grey-backed storm petrel is a small seabird that breeds around the Southern Ocean, including known New Zealand breeding sites in the Chatham Islands and the subantarctic Auckland Islands, Antipodes Island, and Campbell Island. Evidence that grey-backed storm petrels also breed in Fiordland has accumulated since the 1960s, and was summarised in a publication by three Te Papa staff members in 2017.

Dark-coloured bird sitting on the ground with feet splayed surrounded by grass
Grey-backed storm petrel, Rangatira Island, Chatham Islands. Photo by Colin Miskelly

The article was prompted by sightings of at least three grey-backed storm petrels during a Te Papa expedition to Dusky Sound in late 2016. We also summarised 14 previous records of at least 18 birds from Fiordland. These records included two fledglings with down still attached, indicating local breeding.

Signs of incubation

Several fingers spreading grey feathers on the underside of a bird to show bare skin
Grey-backed storm petrel with bare brood patch, Chalky Inlet, November 2017. Photo by Alan Tennyson. Te Papa

Developments since 2016 have included five birds seen in Chalky and Preservation Inlets (south of Dusky Sound) during a joint Department of Conservation and Te Papa survey in late 2017. We managed to catch one of these birds, and found that it had a bare brood patch. This naked skin on the belly is only free of down when an adult bird is incubating an egg (it allows efficient transfer of body heat) and is a sure sign that the bird has a nest nearby. I also found a stoat-killed grey-backed storm petrel while walking the Routeburn Track (200 km away) a year later.

Dead grey, white and black bird on the grassy ground with blood on the head and neck
Stoat-killed grey-backed storm petrel, Routeburn Track, December 2018. Photo by Colin Miskelly

The distance between these records is a reminder of how vast Fiordland is – and grey-backed storm petrel nests are notoriously difficult to find. I have only ever seen one nest (in 1983!), despite having visited many known breeding sites in the intervening years.

Black and white map of Fiordland, New Zealand with red, yellow, blue, orange, white, black and grey markers on different points of the land. Full New Zealand map as inset.
Grey-backed storm petrel records from Fiordland.
Red = November 2016
Yellow = November 2017
Blue = December 2018
Orange star = Secretary Island
White = earlier August to November records
Black = February to April records including 2 known fledglings
Grey = undated records.
Base map from Notornis volume 64 (p. 112), reproduced with permission of the editor [article title ‘Do grey-backed storm petrels breed in Fiordland?’ PDF, 680kb]
The 2017 article concluded that “Attempting to locate grey-backed storm petrel breeding colonies within Fiordland would be a daunting challenge”. Or maybe it would just require extraordinary good luck . . .

Mysterious sounds in the night

In February 2019, the Department of Conservation deployed several acoustic monitoring devices on 8,140 ha Secretary Island, at the entrance to Doubtful Sound. The devices were intended to pick up calls of tokoeka (South Island brown kiwi), and were left in place for several months. DOC staff member Maddie van de Wetering was tasked with counting the kiwi calls captured by the acoustic monitoring devices. One of the devices (installed at Secretary Lake, high on the island) had captured a series of calls that Maddie did not recognise – and nor did any of the DOC bird scientists who she shared the sound files with.

A green pipe attached to a thin tree trunk by white plastic cable tie and a pink ribbon marker. Green bush and blue sky in the background.
Acoustic monitoring device installed at Secretary Lake, Secretary Island. Image: Colin Miskelly. Te Papa

Maddie eventually forwarded the sound files to the Birds New Zealand Records Appraisal Committee as an Unusual Bird Record, which is when they came to my attention. The calls were made late at night, in early March. I did not recognise them either, but wondered whether they could be the begging calls of a grey-backed storm petrel chick, made when one of its parents returned to the nest chamber under the cover of darkness. It was the right time of year, the right open habitat (grey-backed storm petrels are not known to nest under forest) and the right time of day/night. Unfortunately, no one knows what a grey-backed storm petrel chick sounds like!

Sound file: Mystery bird call from Secretary Island, March 2019

Although it would be remarkably good luck for an acoustic monitoring device to be placed by chance near a grey-backed storm petrel nest, Secretary Island has several characteristics that make it a plausible site for these tiny, vulnerable seabirds to breed at. It is very high (it is the third highest island in New Zealand, after the South Island and the North Island), meaning that it has extensive tussock habitat above the bush-line. By good fortune, the island has never been colonised by rats or mice (it is the second largest island in New Zealand that has never had rodents, after Adams Island in the Auckland Islands). And stoats have been suppressed to near zero density by intensive trapping since 2005.

Looking down a grassy mountain at a lake and sea with inlets and coves, surrounded by green mountains and low cloud. A boat is on the water near the centre of the image.
Secretary Lake and Thompson Sound, viewed from Mt Grono, Secretary Island. Photo by Colin Miskelly. Te Papa

Dogged determination

The mystery calls, and knowledge of the island’s conservation history, were sufficient to entice me back to Fiordland. But knowing how difficult grey-backed storm petrel nests are to find, I enlisted the help of conservation dog-handler Jacinda Amey and her DOC-certified seabird dog Poppy. Hopefully if we could get Poppy to a site where the storm petrels were breeding, her sensitive nose would show us where the nests were.

A woman wearing shorts and a high-visibility vest is carrying a pack up stony and grassy terrain. Near her is a brown marker stick with an orange flag. There is a black and white dog in the foreground wearing a high-visibility vest.
Jacinda Amey and her conservation dog Poppy searching for storm petrels on Secretary Island. Photo by Colin Miskelly. Te Papa

The next challenge was getting to Secretary Island. Fortunately, we were able to join a DOC stoat-trapping trip with boat and helicopter support. DOC staff member Pete McMurtrie manages the stoat control/eradication project, and has been involved since the outset. He was as keen for nesting storm petrels to be found on the island as we were.

A green, white and yellow boat is anchored in the dark water, with dark green trees in the background.
The Department of Conservation vessel Southern Winds that we travelled on to Secretary Island. Photo by Colin Miskelly. Te Papa

It was a drizzly day when we were dropped off on the shore of Secretary Island for the long walk up to Secretary Lake. We had precise instructions on where the acoustic monitoring device had been installed (near the hut we would be based in), but found nothing there.

A dark green hut is on the side of a mountain slope covered in alpine grasses and dead branches. A dark mountain ridge behind it.
The hut at Secretary Lake, Secretary Island. Photo by Colin Miskelly. Te Papa

The next day was fine and clear, allowing us to climb to the top of Mt Grono (1196 m) and search the alpine tussock fields on its slopes. Another two days were spent searching areas of low vegetation around Secretary Lake and a rocky area overlooking Thompson Sound, and we used a powerful searchlight shining into the night sky, in the hope of attracting any storm petrels returning to or departing their nests.

Two young kea sit on a rock above a black and white dog standing in the alpine grass. The dog is wearing pink muzzle and an orange high-visibility vest.
Two young kea taunt conservation dog Poppy on Secretary Island. Photo by Colin Miskelly. Te Papa

Nothing to see here

Despite this effort, we found no evidence of any petrel species on Secretary Island. No nests, no flying birds, no calls, no corpses, no feathers. It was a spectacular setting to explore, but we failed to find our target species.

Grey computer-generated 3D map in style of a mould, surrounded by blue water. There are blue, pink, purple, yellow and green trails marked on the map.
Areas covered by dog search on Secretary Island, 18–22 Feb 2020. GPS tracks courtesy of Jacinda Amey

The identity of the calls recorded in March 2019 remains a mystery. They may have been of a grey-backed storm petrel, as there are several reasons why a nest at the same site could have failed to produce a chick in 2020. We found several kea feathers at the acoustic monitoring device site when we arrived, and twice saw kea at the site at night. Kea are known to excavate other petrel chicks from their nests and to eat them (Hutton’s shearwaters in the Seaward Kaikoura Mountains). Weka (another potential predator) were common at the site, and the 2019–20 season was a plague year for stoats in Fiordland. Heavy beech seed fall in 2019 lead to an explosion in mouse numbers. This super-abundant food supply meant that stoats born in late 2019 also had very high survival rates, and stoat capture rates on several Fiordland Islands – including Secretary Island – were much higher than normal. Perhaps a predator had destroyed the nest, and any others in the vicinity.

Where to next? We re-installed an acoustic monitoring device at the same site in February 2020, which will be retrieved during the next (post-COVID-lockdown) stoat trapping trip to the island. We wait with interest whether it has picked up more of the mystery calls, or whether the calls are picked up in future seasons.

With thanks to Maddie van de Wetering for her efforts to identify the mystery calls, the Friends of Te Papa for contributing to costs, Pete McMurtrie and the Te Anau Department of Conservation team for logistic support, and of course Jacinda Amey and Poppy for their determined efforts and good company in the field.

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