A Te Papa team recently visited the Snares Islands, 105 km south-southwest of Stewart Island, where they completed a range of seabird research projects. The most time-consuming task was a re-survey of the vast sooty shearwater (titi, or muttonbird) population there. Estimating the population size was based on two main parameters – the number of burrow entrances over the entire island (counted in plots and transects), and an estimate of burrow occupancy. One of the methods used to ascertain burrow contents is with a burrowscope – a small video camera on the end of a long tube. Here, Colin Miskelly (Curator Terrestrial Vertebrates) describes some of the subterranean inhabitants of the Snares Islands
Sooty shearwaters dominate the Snares Islands’ bird fauna in terms of sheer numbers and biomass. The numbers of birds that arrive each evening are staggering, as they arise from rafts offshore and wheel over the canopy. Peak laying is in late November, and so the birds we saw were a mix of those returning to lay or take the first incubation shift, and pre-breeders searching for a burrow or mate. While the smaller petrel species wait until it is fully dark before coming ashore (to avoid predatory skuas), many sooty shearwaters land before dark and start their incessant caterwauling.
The enormous size of the sooty shearwater population (1-2 million pairs), along with their large body size and aggressive nature means that the smaller species of burrowing petrels that breed on the Snares are excluded from most of the prime deep soil sites.
The second-largest burrowing petrel species on the Snares Islands is the mottled petrel (korure). Most nest under tussock grass in thin soils near the cliff edge. We saw few during our visit, as most were still at sea, with the majority likely to lay in the week or so after we departed.
After the sooty shearwater, the most abundant bird on the Snares Islands is the much smaller common diving petrel (kuaka) – but their population would be almost impossible to survey in any detail. While many have discrete burrows on steep banks and in muddy areas, a large proportion of the population nest in small side chambers inside sooty shearwater burrows, entering through the same large entrance as the much larger shearwaters.
Two species of prion nest on North East Island (the largest island in the group, and where we were based). While both species are often found in soil burrows elsewhere, most prions on the Snares Islands nest in rock tumbles and caves.
Fairy prions (titiwainui) remain as abundant on the Snares Islands as they were in the 1980s, but broad-billed prions (parara) are now much scarcer. This was the main species affected by the huge storm of July 2011, which was estimated to have killed over 200,000 broad-billed prions, plus lesser numbers of the five other prion species (see Te Papa blog links below). We had to work hard to find the ten broad-billed prion chicks we were seeking for collection of blood samples, to allow genetic comparison with the storm-wrecked birds.
Other Snares Island biodiversity blogs
Other blogs in this series
Te Papa prion blogs