Seabird Super Highway - a return to the Hauraki Gulf
by Dr Emma Cronin
Once upon a time, not so long ago, seabirds thrived on our mainland, both along our coasts and far inland where they returned annually to breed. Formerly estimated to number 1.2 billion, seabird numbers plummeted following the arrival of humans, the introduction and spread of predators and extensive habitat clearing.
Of 359 seabird species worldwide, 140 species (more than a third) occur within New Zealand’s Exclusive Economic Zone (out to 200 nm from the coast), with 86 of these species endemic or native to New Zealand1. Such rich biodiversity has bestowed on New Zealand the title of ‘Seabird Capital of the World’, but almost half of these species (46%) are threatened – a higher percentage than in any other country.
But seabirds are once again returning to former breeding sites both on the mainland and on our offshore islands where pests have been eradicated or managed to enable successful breeding populations of seabirds.
...rich biodiversity has bestowed on New Zealand the title of ‘Seabird Capital of the World’, but almost half of these species (46%) are threatened...
The number of success stories is growing, as areas become ‘known’ to seabirds, and birds begin to return en masse of their own accord and establish a breeding colony.
Important Bird Areas
New Zealand’s rich seabird diversity has been recognised through a network of internationally recognised Important Bird Areas (IBA) for seabirds. These areas recognise, internationally, sites of special significance for supporting seabirds using a series of global criteria defined by threshold population sizes, ranges and threatened species status. They include areas that support sea, land, shore and water birds, and typically include either specific breeding locations for a species (such as Hirakimata on Aotea/Great Barrier for black petrels) or broader areas encompassing multiple species and sites.
..seabirds are once again returning to former breeding sites ...
Other IBA types include: ‘flyways’, which cover movement of birds to and from a colony (and would otherwise not be included for any significant bird or biodiversity values); and ‘seaward extensions’, which recognise the areas used by seabirds for feeding, maintenance behaviours and social interactions. Seaward extensions also capture the passage of pelagic (oceanic) species to and from colonies and congregations close to breeding islands1.
The Hauraki Gulf has special significance with respect to seabirds. The relative abundance of off-shore islands and the gulf’s productive waters support 27 (about a third) of New Zealand’s seabird species3.
Figure 1. North Eastern North Island IBA seaward extension. The area covers 73,040 km2 and includes the parts of the marine environment used by 14 seabird species for foraging. The seaward boundary is, as far as possible, colony and/or species-specific, based on known or estimated foraging behaviour. Seaward extensions, particularly around islands, such as Aotea/Great Barrier also capture the passage of pelagic species to and from colonies, and congregations close to breeding islands4.
The only known breeding locations for five of these species are located in the Hauraki Gulf: Buller’s shearwaters (Puffinus bulleri); New Zealand fairy tern (Sternula nereis davisae); Pycroft’s petrel (Pterodroma pycrofti); black petrel (Procellaria parkinsoni); and the New Zealand storm petrel (Fregetta maoriana). These and other seabird species are recognised in the identification of 13 globally significant IBAs in the Hauraki Gulf from a total of 210 in New Zealand (141 on land and 69 in marine environment)1.
The relative abundance of off-shore islands and the [Hauraki] Gulf’s productive waters support 27 (about a third) of New Zealand’s seabird species.
The Hauraki Gulf is also included in the proposed ‘North Eastern North Island’ seaward extension IBA (Figure 1). The proposal is triggered by the presence of 14 seabird species; five species with pelagic ranges within the area, five species observed regularly feeding there, and four other species of significance4.
The proposed seaward extension IBA encompasses existing IBAs including the North Auckland Seabird Flyway, Te Hauturu-o-Toi/Little Barrier Island (Cook’s petrel, black petrel and New Zealand storm petrel), Hirakimata, Great Barrier Island (black petrel), Mahuki Island, off Aotea/Great Barrier Island (gannet) and the Mokohinau Islands, north of Great Barrier Island (common diving petrel, grey-faced petrel and white-faced storm petrel and numerous other non-trigger species). These IBAs recognise the special significance of the outer Hauraki Gulf and its links to the inner Gulf including the Auckland region, for seabirds. A further 21 island and mainland IBA sites occur within this seaward extension area4 (Figure 1), signifying the richness of the entire area for seabird biodiversity and its overall value to marine conservation.
The North Auckland Seabird Flyway has been identified owing to the movement of seabirds across the North Auckland Peninsula, particularly Cook’s petrels flying at night between the Tasman Sea and Hauraki Gulf and the New Zealand fairy tern flying from coast to coast. Other seabirds likely to use this flyway include terns, gulls, shags and pelagic species such as black petrel, Pycroft’s petrel and grey-faced petrel4.
Hauturu (Little Barrier Island) is an extremely special location in the Hauraki Gulf and one of the most important reserves of its kind in the world. The island is a veritable ‘Jurassic Park’, supporting a treasure-trove of our rare and endangered land birds, bats, reptiles and invertebrates.
Around 40 species of birds breed there, as well as two bat species and 14 species of reptiles5 in addition to many seabird species. Hauturu is the only breeding site of the endangered New Zealand storm petrel, has 98% of the world’s population of breeding Cook’s petrels, and a satellite population of breeding black petrel6. The Cook’s petrel population increased notably following eradication of kiore on the island in 2004, despite cats being eradicated in the 1980s, and possibly saved the New Zealand storm petrel from extinction.
Seabird recolonisation of Hauraki Gulf islands
Burgess Island in the Mokohinau group (see Box 1) was left to recover naturally following the removal of kiore in 1990. Twenty-seven years later, the island supports seven species of burrowing seabirds.
A recent study of 98 Hauraki Gulf islands8 found that the number of breeding seabird species increased on islands cleared of predators leading to more diverse assemblages of seabirds than uninvaded islands (i.e., islands never having had predators).
Sixteen seabird species were present on cleared islands, whereas 11 species were present on uninvaded islands, and only six species were represented on invaded islands.
The greater seabird assemblage on cleared islands suggests rapid recolonisation by seabirds following the eradication of predators. The smaller average size of uninvaded islands (with less suitable and diverse habitats) may also be contributing to the lower species richness (number) observed.
High potential for Aotea/Great Barrier
The proximity of the Mokohinau’s and Hauturu with their abundant seabird (and other bird and animal) species diversity, and the existing IBAs (and breeding seabird species) on Aotea/Great Barrier Island and Mahuki Island, indicate eradication and/or management of pests on Aotea/Great Barrier and other nearby islands (such as Rakitu) would facilitate rapid re-population of these areas by seabirds.
The considerable size and diversity of habitats on Aotea/Great Barrier Island would help to ‘buffer’ species vulnerability against extreme events and could provide a ‘back-stop’ or refugia for populations on other, much smaller islands.
A network of island and mainland areas providing suitable seabird breeding habitat is vital to alleviate the threatened status of many of our seabird species, to prosper future seabird biodiversity, and to substantiate New Zealand’s status as ‘Seabird Capital of the World’.
The considerable size and diversity of habitats on Aotea/Great Barrier Island would help to ‘buffer’ species vulnerability against extreme events...
Notes:
1Forest and Bird, 2014. New Zealand Seabirds: Important Bird Areas and Conservation. The Royal Forest and Bird Protection Society of New Zealand, Wellington, New Zealand.
2Forest and Bird, 2015. New Zealand Seabirds: Sites on Land, Coastal Sites and Islands. The Royal Forest and Bird Protection Society of New Zealand, Wellington, New Zealand.
3Gaskin, C. P. and Rayner, M. J., 2013. Seabirds of the Hauraki Gulf: Natural History, Research and Conservation. Hauraki Gulf Forum.
4Forest and Bird, 2014. New Zealand Seabirds: Sites at Sea, Seaward Extensions, Pelagic Areas. The Royal Forest and Bird Protection Society of New Zealand, Wellington, New Zealand.
5Department of Conservation website. Retrieved from, http://www.doc.govt.nz/parks-and-recreation/places-to-go/auckland/places/little-barrier-island-nature-reserve-hauturu-o-toi/nature-and-conservation/
6Forest and Bird, 2015. New Zealand Seabirds: Sites on Land, Coastal Sites and Islands. The Royal Forest
and Bird Protection Society of New Zealand, Wellington, New Zealand.
7Ismar, M. H., Baird, K. A., Gaskin, C. P., Taylor, G., Tennyson, A. J.D., Rayner. J., Bettesworth, D., Fitzgerald, N., Landers, T. J., and Imber, M.J., 2014. A case of natural recovery after the removal of invasive predators – community assemblage changes in the avifauna of Burgess Island. Notornis, 2014, Vol. 61: 188-195. The Ornithological Society of New Zealand.
8Borrelle et al., 2016, Influences on recovery of seabirds on islands where invasive predators have been eradicated, with a focus on Procellariiformes, Oryx, doi:10.1017/S0030605316000880
9Alexander Turnball Library. Photographer unidentified. Reference Number: 1/2-114602-F.
http://mp.natlib.govt.nz/detail/?id=83427
10Maritime New Zealand. The history of Mokohinau Islands Lighthouse. http://www.maritimenz.govt.nz/public/history/lighthouses/Mokohinau-Island/#history