Breaksea Island/Te Au Moana in Fiordland is an iconic site for New Zealand conservation. It was one of the first large islands to be cleared of rats, when a team led by Rowley Taylor and Bruce Thomas (of Landcare Research) eradicated Norway rats in 1988.
This ambitious project followed the successful eradication of rats on much smaller (9 hectares) nearby Hawea Island in 1986.
But how has the wildlife on these islands responded to more than 30 years without rats? Vertebrates Curator Colin Miskelly reports on a recent field trip to find out.
170 islands and counting
Since 2016, Te Papa and the Department of Conservation have undertaken three expeditions to survey seabirds and land birds on the smaller islands in southern Fiordland.
The most recent survey, of Te Puaitaha / Breaksea Sound and Tamatea / Dusky Sound, was in December 2019, when 53 islands were searched, bringing the total to more than 170 islands.
The 2019 Breaksea Sound survey differed from the previous two surveys (of islands in Dusky Sound, Chalky Inlet, and Preservation Inlet) because we had good information on the birds that were present before rats were eradicated from Breaksea and Hawea Islands, and stoats prevented from recolonising numerous other islands closer to shore.
A bygone era
Much of this baseline information on bird populations on islands in Breaksea Sound was gathered during 1974 to 1986, before the Department of Conservation and Landcare Research were created as part of the major restructuring of science and government departments under the fourth Labour Government (1984–90).
Before these changes, Taylor and Thomas worked for Ecology Division of DSIR, and they were assisted by Lands & Survey Department rangers Kim Morrison and Ron Peacock from Fiordland National Park.
Recollections of islands teeming with rats
Among the team who cleared Hawea Island rats was a youthful Graeme Taylor – now a senior scientist with the Department of Conservation, and a member of our team.
Graeme’s recollections of rat-infested islands more than 30 years earlier added depth and colour to the changes in the bird communities that we discovered.
Breaksea Island – a Specially Protected Area
In addition to being one of the first large islands to be cleared of rats, Breaksea Island was a pioneer site for translocations of rare birds.
Tieke (South Island saddlebacks) from Big Island and Kundy Island (west of Stewart Island) were released there in 1992, and mohua (yellowheads) from the Blue Mountains, West Otago, were released there in 1995.
South Island robins (kakaruai) survived naturally on Breaksea Island, and these three species along with bellbirds are now the most abundant forest bird species on Breaksea Island.
The island has subsequently been the source of robins released on Anchor Island, Pigeon Island, and Indian Island, tieke released on South Passage Island, Anchor Island, Chalky Island, and to Orokonui Ecosanctuary, and mohua released on Chalky Island, Anchor Island, Pigeon Island, Whenua Hou/Codfish Island and to the South Branch, Hurunui River.
Robins are stronger fliers than tieke and mohua, and have colonised several islands up to 4 km from Breaksea Island since stoats were removed from Resolution Island and surrounding islands in 2008.
They are now common on the inner Gilbert Islands and Entry Island, and have apparently out-competed other insectivorous bird species (including tomtit and dunnock) that are now rare or absent on these islands.
This ‘trophic cascade’ effect has been documented at other restoration sites (e.g. Zealandia Sanctuary in Wellington), where removal of mammalian predators has allowed deep endemic bird species to flourish and to out-compete other bird species.
The main seabird species that we searched for was the bizarre-looking broad-billed prion.
This small burrow-nesting petrel was hugely abundant when Captain Cook and the naturalists accompanying him surveyed nearby Tamatea / Dusky Sound in 1773, but most of the Fiordland populations have been wiped out by introduced rats and stoats.
On top of this ongoing decline, a severe winter storm in 2011 killed more than 200,000 broad-billed prions, and we have little information on which breeding sites these birds were from.
During the 1980s, broad-billed prions were known to breed on two small islands in Breaksea Sound. We were able to confirm their presence at four additional sites, including on Breaksea Island itself, as the birds start to recover from more than 200 years of predation by rats and 100 years of stoat presence on some of the islands.
Fur seal recovery
One species that has had a spectacular recovery in Fiordland is the New Zealand fur seal, that was last hunted in 1946.
They were scarce on the islands in Breaksea Sound in the 1980s, but are now numerous enough on some islands to complicate our survey efforts.
December is the peak of their breeding season, with bulls aggressively defending their harems and breeding territories.
At several sites it was a challenge to find a safe route from the shoreline to the vegetation where burrow-nesting seabirds could be breeding.
Department of Conservation guidelines are to stay at least 20 metres away from seals, which we were happy to comply with – if only the seals did too!
On three of the outer islands their breeding territories were contiguous around the shoreline and well into the island interior, and some breeding bulls would charge from more than 20 metres away to evict us from their territories.
Fortunately, I had come forewarned and prepared, with a Seal Deterrent Device (aka a golf umbrella).
Suddenly unfurling the brightly-coloured umbrella stopped most of the rapidly approaching seals in their tracks, but my companions were too busy laughing or retreating (rapidly) to get good images or video of the effectiveness of the SDD.
An abundance of weevils
In addition to surveying for birds, we also searched for evidence of lizards and two species of large flightless weevils.
Before 2016 there was only a single known natural population of flax weevils in Fiordland.
We found evidence of their presence on an additional 17 islands in Breaksea Sound in 2019, but it is unknown whether this represents a true recovery, or whether they were simply overlooked previously.
As previously, the Te Puaitaha / Breaksea Sound survey was reliant on superb logistic and boat support by the crew of the DOC vessel Southern Winds, and thanks also to our team member and author Peta Carey who generously supplied images for this blog.