A plethora of islands – surveying breeding seabirds in Fiordland

A plethora of islands – surveying breeding seabirds in Fiordland

A team comprised of staff from Te Papa and the Department of Conservation (DOC) recently spent a week surveying islands in northern Fiordland. In this second blog based on the trip, vertebrates curator Colin Miskelly describes some of the sites visited and discoveries made.

A boat on water with mountains in the background and dark overhanging leaves in the foreground.
The Department of Conservation vessel Southern Winds (shown in Charles Sound) was used for all four boat-based surveys 2016–20. Photo by Jean-Claude Stahl. Te Papa

There are a lot of islands in coastal Fiordland. A quick look at a map of the region shows 50 named islands and another 22 named clusters. There are 18 islands in the appropriately named ‘Many Islands’ in Dusky Sound alone. And then there are all the unnamed islands, islets, and rock stacks.

One man in wet-weather gear in an inflatable dingy close to rocks where two people in dark clothes and life jackets are standing.
Team members departing from an unnamed island in Dagg Sound, November 2020. Photo by Jean-Claude Stahl. Te Papa

Homes for seabirds

Any island large enough to have rock crevices or soil (for burrowing) could provide a breeding site for petrels. Petrels are a diverse group of seabirds, with 37 species breeding in the New Zealand region, nearly all of which nest in burrows excavated in soil.

The three most abundant and widespread species in Fiordland are sooty shearwater (tītī), broad-billed prion (pararā) and mottled petrel (korure). Finding their colonies has been the focus of a series of expeditions by Te Papa and DOC staff since 2016.

A round island made of rock with trees on the top sits in the sea in front of a bush-clad cliff face in the background
This unnamed island in Dagg Sound had an estimated 2800 sooty shearwater burrows. Photo by Jean-Claude Stahl. Te Papa

The seabird surveys started in Dusky Sound (which is rumoured to have an island for every day of the year), then moved to the nearby island-rich fiords of Chalky Inlet, Preservation Inlet, and Breaksea Sound. By early 2020 we had completed surveys of 175 islands in southern Fiordland, and so shifted our gaze further north.

A small boat on the water in between bush-clad hills and rocks in the background, and rocky terrain in the foreground.
Eleven islands in the Shelter Islands, Doubtful Sound, were included in the November 2020 survey (Secretary Island in the background). Photo by Alan Tennyson. Te Papa

Big mountains and few islands

The remaining section of the Fiordland coast has about 125 km of coastline, from Dagg Sound north to Milford Sound. A feature of Fiordland is that as you go north, the mountains get higher, the fiord sides get steeper, and there are fewer islands. The northernmost fiord of Milford Sound is famed for its spectacular scenery. The only island in the outer fiord (Post Office Rock) is an infinitesimal speck among this grandeur, yet we found 73 sooty shearwater burrows there.

A small rocky island covered in trees sits in blue sea next to a bush-clad piece of land. There are mountains in the background
Post Office Rock, Milford Sound. Photo by Jean-Claude Stahl. Te Papa

Northern limits

We started the survey at Deep Cove in Doubtful Sound, and immediately headed north to Milford Sound, to make the most of a few days of settled weather. As we worked our way southward, one of the highlights was landing on an unnamed island in Poison Bay, just south of Milford Sound.

Not only was it an important tawaki/Fiordland crested penguin breeding site, but we found broad-billed prions breeding there, more than 50 km north of where they were known to occur in Fiordland.

Eight penguins with yellow stripes at their eyes standing on rocks facing different directions
Fiordland crested penguins on an unnamed island in Poison Bay, November 2020. Photo by Colin Miskelly. Te Papa
A fluffy grey chick sits in a hand held up in front of flax-covered land. There's a cove and bush-clad hills in the background.
Broad-billed prion chick, unnamed island in Poison Bay, November 2020. Photo by Alan Tennyson. Te Papa

A few days later we discovered another range extension, with about 50 mottled petrel burrows (and two corpses) on Seymour Island in Doubtful Sound – the first report of this species breeding north of Breaksea Sound in recent times.

Two dead grey and white birds lying on brown leafy undergrowth.
Mottled petrel corpse, Seymour Island, Doubtful Sound, November 2020. Photo by Alan Tennyson. Te Papa

A nasty surprise

Most of the islands in northern Fiordland do not receive any pest control, and are close to the mainland, and so it was not a surprise to find evidence of rat presence. This included footprints, droppings, and gnawed seabird corpses.

However, we were very surprised to find rats to be present on Nee Island, off the south-west corner of 8140 ha Secretary Island, at the entrance to Doubtful Sound.

Secretary Island is the largest island near mainland New Zealand that has never had rats or mice establish. It is also the site of a major island restoration project by DOC, with red deer eradicated, and an extensive network of stoat traps maintained 3-4 times a year. Nee Island lies only a few hundred metres offshore, which is far too close for comfort.

Four animal footprints in wet mud.
Rat footprints in mud on Styles Island, Caswell Sound, November 2020. Photo by Colin Miskelly. Te Papa

Within 12 days of our visit, DOC staff had returned to Nee Island, had used traps and trail cameras to confirm the presence of Norway rats, and had hand-spread brodifacoum bait to eradicate the rats.

Trail-cam still of a Norway rat on Nee Island, November 2020. Photo courtesy of Department of Conservation

Funky weka

One of my personal highlights was landing on western Shelter Island, at the entrance to Doubtful Sound. I last visited the island (as a DOC scientist) in July 1993, as part of a weka genetic sampling project.

The weka on the Shelter Islands are mainly the black colour morph (black is the predominant colour for weka in coastal Fiordland). However, a few birds in 1993 had a mixture of black and white feathers, presumably due to a genetic mutation. My 1993 notes describe one bird caught on this island as having “about half the head and underparts white”.

I photographed an almost identical bird on the same island in November 2020, indicating the persistence of this genetic mutation in the population for at least 27 years.

A black and white bird in the middle of leafy ground cover.
Partially leucistic weka on western Shelter Island, November 2020. Photo by Colin Miskelly. Te Papa

The last island

We spent the last night of the survey at the head of Hall Arm, close to the Southern Winds’ home port of Deep Cove. There was only one island left to complete the survey – Rolla Island (0.8 ha) at the entrance to Hall Arm.

It was a great feeling to step ashore on this beautiful little island, knowing that we had managed to land on every island on our target list for the entire Fiordland coast over the course of the four surveys.

A small tree-clad island in the foreground with a bushy mountain with a waterfall in the background
Rolla Island – the 217th and last island surveyed. Photo by Jean-Claude Stahl. Te Papa

Looking back

Before we started the surveys in 2016, there were only about a dozen Fiordland islands where petrels were known to breed, and no population estimates for any site.

The underside of a bird flying at night with its wings spread
Mottled petrel in spotlight beam, Doubtful Sound, November 2020. Photograph: Jean-Claude Stahl, Te Papa

After landing on 217 islands, we now know that there are at least 165 petrel colonies in Fiordland, and probably more than 66,000 breeding pairs. This is far more than anyone expected, and provides a great springboard for these populations to recover as rats and stoats are cleared from more and larger islands, and from the adjacent mainland.

Previous Fiordland seabird blogs

Storm petrels in the spotlight

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

The call of the wild – attracting seabirds to remote Coal Island

Fiordland’s Breaksea Sound: 30 years after the rats

Seabird discoveries in remote southern Fiordland

The petrels of Dusky Sound

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