Te Papa vertebrate curator Dr Colin Miskelly recently spent 12 days on Ohinau Island (east of Whitianga, Coromandel Peninsula) as part of a Te Papa seabird research team studying flesh-footed shearwaters. This blog reports on the seabird species found on the island and nearby Ohinauiti Island.
Ohinau is a 43 ha forested island owned by Ngati Hei, and lying about 7 km south of other islands in the Mercury Island group. The island formerly held populations of Pacific rats (kiore), mice and rabbits, but has been free of introduced mammals since these were eradicated by Ngati Hei and the Department of Conservation (DOC) in 2005. Ohinau is an important breeding site for flesh-footed shearwaters, and they were the reason that Te Papa researchers visited the island for 5 weeks from mid January 2014.
The flesh-footed shearwater is a large all-dark shearwater with a bicoloured bill and pale pink legs. Shearwaters are petrels, and six species of shearwaters are common in New Zealand coastal waters. Perhaps the best-known species is the sooty shearwater – the muttonbird harvested on islands around Stewart Island. All the New Zealand species breed in burrows that they excavate in soil, visiting their colonies at night, and laying a single egg per annum.
Flesh-footed shearwaters are familiar to most boat-based recreational fishers off northern New Zealand – even if they don’t know their correct name. They are the dark birds that have the often annoying habit of diving after baited hooks as they are lowered to the depths. This scavenging habit is the shearwater’s undoing, as they get hooked and drown on commercial longlines, and there is evidence that some recreational fishers deliberately cause traumatic and fatal injuries to the persistent birds. Concern at the declining population numbers of flesh-footed shearwaters provided the background to our visit – to assess the population size on Ohinau, and determine where the adult birds were foraging at sea. The work was funded by DOC utilising funds from a levy on commercial fishing companies, to investigate ways to mitigate their impacts. Knowing where the birds forage should allow more targeted mitigation and advocacy.
Flesh-footed shearwaters were the most common seabird on Ohinau Island in January-February, when their eggs were just hatching, but we found evidence that at least five other petrel species (including two other shearwater species) bred there or on nearby Ohinauiti Island. The other species all breed earlier in the season, and some had already fledged their chicks and departed to sea.
Fluttering shearwaters were heard in flight most nights, but the only burrows we found on Ohinau contained failed eggs or evidence of recently-departed chicks. A few live chicks were seen on Ohinauiti Island on 24 January. Fluttering shearwaters are the familiar small brown-and-white shearwaters of inshore waters around the North Island and the Marlborough Sounds, including in Waitemata and Wellington Harbours.
The third shearwater species that breeds on the Ohinau Islands is the winter-spring breeding little shearwater. We found dead chicks on both islands, but saw no live birds.
The grey-faced petrel is another winter-spring breeding species that was absent during our visit. We found one dead adult and one dead chick.
Two smaller petrel species breed on the Ohinau Islands. Ohinauiti holds a dense population of white-faced storm petrels, and common diving petrels breed on both islands. We found a dead diving petrel chick on Ohinauiti, and burrows presumed to be of diving petrels on two rock stacks accessible at low tide from Ohinau Island.
The most exciting seabird discovery of our visit was that at least one Pycroft’s petrel was visiting a burrow on Ohinau Island at night, and they were occasionally heard calling in flight at night. This rare gadfly petrel has its stronghold on the nearby Mercury Islands, but had not been recorded on Ohinau Island previously. The presence of Pycroft’s petrels on and over Ohinau Island is an encouraging sign that they may recolonise naturally following the 2005 rat eradication.
Several other ‘non-petrel’ seabird species were seen every day on or around Ohinau Island. Little penguins had finished breeding for the year, but were seen and heard along the shoreline each night, and one was found in a burrow during the daytime.
Large flocks of red-billed gulls fed over surface shoals of trevally offshore every day (often with accompanying fluttering shearwaters and white-fronted terns), presumably feeding on Nyctiphanes krill that the fish drove to the surface. The flocks were occasionally accompanied by a few Buller’s shearwaters and Arctic skuas (the latter chasing the terns). However, Australasian gannets and black-backed gulls were more interested in larger prey, and foraged independently.
Although we found no evidence of a shag breeding colony on Ohinau Island, pied shags were common, with up to 43 roosting together on rocks offshore.
With thanks to Ngati Hei for permission to visit Ohinau and Ohinauiti, and Sarah Jamieson (Te Papa) and DOC for logistic support. Rob Chappell (DOC) and Susan Waugh assisted with field work on Ohinauiti, and Robyn Blyth, Lizzy Crotty and Liam Miskelly on Ohinau (with Susan Waugh, Ingrid Hutzler, Alison Burnett and Simon Hayward in previous or subsequent teams).