Four Te Papa staff members visited the Snares Islands Nature Reserve for a fortnight in late 2013, undertaking a variety of seabird and plant research projects (see previous blogs listed below). The Snares Islands are famous for their birdlife, and here vertebrates curator Colin Miskelly looks at some of the species that are unique to the islands, or have strongholds there.
The islands lie 105 km south-southwest of Stewart Island, and were originally named simply ‘The Snares’ by Captain George Vancouver when he discovered them in November 1791. Vancouver considered the islands to be a hazard to shipping, hence the sinister name. The two main islands are covered with tree-daisy forest and tussock grassland. As the islands have never had introduced mammals establish, the wildlife is both abundant and approachable.
The bird fauna is dominated by seabirds, particularly the phenomenally abundant sooty shearwater, which nests in burrows wherever the soil is deep enough. A previous blog described how the Te Papa team re-surveyed the size of the Snares Islands sooty shearwater population, and also illustrated the four other burrow-nesting petrel species present. These five petrel species (sooty shearwater, mottled petrel, common diving petrel, fairy prion and broad-billed prion) all visit their burrows at night, and so it is other species of seabirds that are most conspicuous during the day.
Perhaps the most well-known bird species on the islands is the Snares crested penguin. As its name suggests, it breeds only within the Snares Islands, where it breeds on the two main islands (North East Island and Broughton Island), plus on two islets of the Western Chain, 5 km to the south-west. One of the enduring mysteries of Snares Island birdlife is why the crested penguins on the Western Chain breed six weeks later than those on the main island – are they a cryptic species awaiting ‘discovery’?
The two main species of albatross that breed on the Snares Islands are Buller’s mollymawk and Salvin’s mollymawk. The smaller Buller’s mollymawk breeds on any island or islet in the group that has at least some vegetation, while Salvin’s mollymawks nest solely on two islets of the rocky Western Chain (Toru & Rima Islets – the same islets as the penguins). About 8700 pairs of Buller’s mollymawks breed on the Snares Islands, laying mainly in January-February, with chicks departing during August-October. We were on the islands during the short gap between breeding seasons, and saw only a few early birds returning to reclaim their nest sites. In contrast, the Salvin’s mollymawks had downy chicks when we landed on Toru Islet on 28 November. While the Snares Islands are a major breeding site for Buller’s mollymawk, the main Salvin’s mollymawk breeding site is on the Bounty Islands about 900 km east of the Snares.
Unlike the other small petrels on the Snares, which nest out-of-sight in burrows and rock crevices, the Cape petrel nests mainly in the open on cliff ledges. This would make the adults and chicks vulnerable to predators, especially skuas, but the Cape petrels have a very effective anti-predator response. They vomit smelly stomach oil with sufficient accuracy and range to deter predators or people from approaching too close.
The top predator on the Snares Islands is the subantarctic skua, which looks similar to a large, heavily-built gull. During the breeding season skuas feed almost entirely on seabirds, particularly the five burrow-nesting petrel species. The Te Papa team put a lot of effort into locating and identifying skua prey remains in an effort to see whether the proportion of broad-billed prions consumed had declined since the massive prion mortality event that occurred in July 2011.
Antarctic terns breed as isolated pairs or in small colonies around the Snares Islands coastline, stridently and aggressively defending their nest sites from skuas and gulls. These striking birds breed on all of New Zealand’s subantarctic islands, plus on some of the muttonbird islands south-west of Stewart Island. Somewhat surprisingly, they have never been recorded from the North or South Islands only a short distance away.
Fernbirds on the main islands of New Zealand stay mainly among dense wetland vegetation. However, the endemic Snares Island subspecies spends much of its time in the open, busily foraging on the ground. They are fearless of larger animals, often walking over resting New Zealand sea lions to catch blowflies. While they frequently fly short distances, it is unusual to see a Snares Island fernbird fly more than 10 metres.
The endemic Snares Island tomtit is easily distinguished from other populations of New Zealand tomtits by its all-dark plumage. Both the tomtit and fernbird are common along the shoreline of the sheltered east coast of the Snares Islands, and so are readily seen by ecotourists zodiac-cruising close offshore. The Department of Conservation administers the Snares Islands Nature Reserve, and landing permits are limited mainly to conservation managers and approved researchers. Tourists visiting the islands are able to see much of the wildlife from zodiacs, as well as exploring spectacular sea caves and tunnels.
The most secretive of the Snares Island endemic birds is the Snares Island snipe – a bird that I have a particular fondness for. I had the privilege of studying snipe (mainly on the Snares) for my PhD thesis, and in 2005 participated in a translocation of snipe from the Snares Islands to Putauhinu Island (a muttonbird island south-west of Stewart Island). Snipe formerly occurred throughout the main islands of New Zealand, but their vulnerability to introduced predators has resulted in their current restricted distribution on a few outlying islands.
For more information, see Birds of the Snares Islands, New Zealand.
Te Papa Snares Islands blogs
Science Live: Expedition Snares Island