Seabirds are birds that obtain all or nearly all of their food at sea. There are just 360 species of seabird out of a total of 9,000 bird species worldwide. Of this 360, 86 breed in the New Zealand region, including 38 (10% of the world total) which breed nowhere else. A further nine migratory species breed elsewhere but visit New Zealand each year, and a number of others are recorded in New Zealand waters from time to time. With a greater diversity of seabirds than anywhere else, New Zealand can rightfully claim to be the world's seabird capital. New Zealand’s seabirds include penguins, albatrosses, petrels, shags, gannets, terns and skuas.
A few seabird species in New Zealand are amazingly abundant. The most numerous is probably the sooty shearwater (Puffinus griseus), more commonly known as the muttonbird, or tītī in Māori. No systematic count has ever been made; however, in the 1970s it was estimated that there were 2.75 million breeding pairs on the Snares Islands, 100 kilometres south of Stewart Island. Including non-breeding birds and chicks, the total came to more than 7.5 million. To put this into context, there are only 3 million breeding pairs of seabirds in the entire British Isles. Sooty shearwater numbers may have declined by up to 37% since this estimate, but even so they remain the most populous bird in the country – far more numerous than the sparrows (Passer domesticus) and starlings (Sturnus vulgaris) New Zealanders see every day. Fairy prions (Pachyptila turtur) and white-faced storm petrels (Pelagodroma marina) are also exceedingly plentiful on certain offshore islands that are free of rats.
This abundance and diversity is a result of New Zealand’s rich marine environment. The New Zealand region extends from the subtropical waters around the Kermadec Islands to the cool, subantarctic waters of the Campbell Plateau. The subtropical convergence, where the so-called subtropical waters and subantarctic waters meet, extends around the southern shores of the South Island and east to the Chatham Islands. These conditions combined with the topography of submarine landforms create areas of upwelling where nutrients, fish and seabirds are abundant. One such area is along the Kaikōura coast. A diversity of marine life exists here because the sea floor goes abruptly from shallow to deep, creating a range of different habitats within a small area.
Being a seabird is a specialised occupation. Of the 24 bird orders (groups of related species), only five have seabirds among their members. Seabirds in New Zealand come from four of these orders:
Penguins belong to the order Sphenisciformes. Three of the world’s 17 species breed on the New Zealand mainland, and a further three on the subantarctic islands. Penguins live only in the southern hemisphere. Of all the birds, penguins are the most accomplished divers, with some species capable of reaching depths of 100 metres or more. Their small wings or flippers, stiff oily plumage, dense bones and thick fat deposits are all adaptations to diving. They catch fish, crustaceans (such as krill) and squid by underwater pursuit.
The most familiar ‘seabirds’ are the gulls, but because they find much of their food on land and seldom venture far from shore they are not true seabirds. The black-billed gull, black-fronted tern and some shags are often found around fresh water. The wading birds such as oystercatchers, godwits and herons which feed in estuaries or along the shoreline are not regarded as seabirds. No New Zealand duck is primarily marine, with the possible exception of the extinct New Zealand merganser (Mergus australis).
The order Procellariiformes is arguably the most successful seabird order, with about 124 species and living in all the world’s oceans. They range in size from tiny 35-gram storm petrels to huge albatrosses weighing in at 9 kilograms, with a 3-metre wingspan. These birds find all their food at sea, and most species come to land only to breed. Petrels and shearwaters are adept divers – some shearwaters regularly dive to 60 metres. Storm petrels, prions and albatrosses obtain their food close to the water’s surface.
Pelecaniformes is the most variable seabird order. Its members include gannets and shags (cormorants), as well as pelicans, frigate birds and boobies. Species from the latter three groups of seabirds live on New Zealand’s Kermadec Islands and occasionally stray to the mainland coasts.
Three species of New Zealand shag live primarily in freshwater habitats, harbours and estuaries. The other nine species are exclusively marine, with some also making use of estuaries and harbours. All but one of the marine shags are endemic to New Zealand – they live nowhere else. The other four species occur in other countries as well as New Zealand. All but one of the endemic species have restricted ranges, being confined to particular island groups or to limited parts of the New Zealand mainland. Shags pursue their prey under water, using their feet to propel themselves.
Australasian gannets (Morus serrator) breed at 24 sites around the New Zealand coast, the best-known colonies being at Muriwai (near Auckland), Cape Kidnappers in Hawke’s Bay and on Farewell Spit. Gannets sight fish while flying overhead and capture them by plunging into the water.
Most members of the order Charadriiformes are not marine species. Gulls and some terns take a large proportion of their food ashore or from freshwater habitats. Black-billed gulls and black-fronted terns breed by braided rivers and some larger lakes, and many visit the coast in winter. However, some tern species and all skuas are largely marine, and both of these groups have New Zealand representatives. This order also includes the phalaropes that occasionally stray into New Zealand waters, and the auks which live only in the northern hemisphere.
Marine terns such as the white-fronted tern (Sterna striata) feed by dipping – hovering above the water then dropping to catch surface-shoaling fish.
Skuas are well-known predators of eggs, chicks and small birds at seabird colonies, but they do in fact take a large proportion of their food at sea. In the New Zealand region subantarctic skuas (Catharacta antarctica) breed around Stewart, Chatham and the subantarctic islands. Four other species visit New Zealand waters each year, including the small Arctic-breeding skuas which obtain much of their food by harassing terns, inducing them to regurgitate their food.
It is not easy for birds to get all the food they need from the sea. Except for along the shoreline, primary productivity (photosynthesis) is carried out by tiny phytoplankton. These are eaten by small zooplankton, which in turn are eaten by larger invertebrates or fish – only then is food available to seabirds. Photosynthesis requires light and only occurs in the upper layers of the water, and because nutrients (including mineral and organic compounds) tend to sink to the dark sea floor, oceans are much less productive than the ecosystems on land. Nutrient-rich patches (where algae can grow) are created where nutrients are stirred towards the surface by currents, convergences, wind, abrupt changes in depth, or combinations of these. Out in the open sea these oases tend to be far apart, and seabirds have to forage widely, often travelling for hundreds or even thousands of kilometres.
Flying and diving require very different types of bodies. Birds that fly well enough to cover large areas in search of scattered food resources are generally unable to dive deeply, and are restricted to feeding in the top few metres of the ocean. Albatrosses, the most adept of the seabirds at flight, float like corks when they alight on the water and can manage only shallow dives at best. On the other hand, birds that dive well such as penguins and diving petrels have compromised the ability to fly. Penguins’ heavy bodies and reduced wings allow them to dive to greater depths and swim more efficiently than other birds, but to achieve this they have lost the power of flight altogether.
Shearwaters are perhaps the consummate seabirds. Of medium size (weighing 300–800 grams) and with stiff, oily feathers, some species can dive to about 60 metres – as deep as some penguins – and forage as far out to sea as albatrosses.
No bird can incubate its egg at sea, so the places where seabirds breed are inevitably separated from where they find food. This means that vast numbers of breeding seabirds make use of the islands which are close to rich feeding areas. The Snares Islands are strategically located within foraging distance of feeding zones, and the birds which breed there include millions of sooty shearwaters (muttonbirds or tītī), thousands of Buller’s albatrosses (Thalassarche bulleri), Snares crested penguins (Eudyptes robustus), various small petrels and smaller numbers of Antarctic terns (Sterna vittata), subantarctic skuas and gulls.
Likewise, a variety of seabirds breed tightly packed on the predator-free ground and rock stacks of the Chatham Islands, the Bounty Islands and some islands around the New Zealand mainland. Large populations once existed on the South and North islands before the first mammalian predators arrived with humans around 1300 AD.
While shags and gulls seldom venture more than about 10 kilometres from land, albatrosses, shearwaters and petrels regularly travel thousands of kilometres from their breeding colonies. Antipodean albatrosses (Diomedea antipodensis), which nest on the Auckland Islands, frequently feed in the middle of the Tasman Sea. They make journeys of over 5,000 kilometres and lasting 11–13 days, while their partners incubate the eggs or their chicks wait on shore for food.
Buller’s albatrosses (also known as Buller’s mollymawks) breeding on the Snares Islands feed in the Tasman Sea or along the east coast of the South Island as far north as Kaikōura. Sooty shearwaters and mottled petrels (Pterodroma inexpectata), which breed in southern New Zealand, feed many kilometres to the south of the country; the shearwaters travel to 60–65º south and the mottled petrels venture as far south as the Antarctic pack-ice zone.
Westland petrels (Procellaria westlandica), which only breed in the hills near Punakaiki, feed mostly along the shelf break between Cape Farewell and Haast. They frequently visit Cook Strait and the Kaikōura coast, and less often the Chatham Rise. In contrast, gannets may range over thousands of kilometres between breeding seasons, but while nesting generally remain within 200–300 kilometres of their colony, with most feeding done within 60 kilometres.
For all seabirds, while one partner is foraging at sea their mate must remain at the nest to incubate the eggs (albatrosses and petrels lay only one egg, penguins two eggs, and shags usually lay three eggs each year). Shags, gulls and terns return at least once every day to relieve their mate. For those species that make long journeys in search of food, one partner may be at sea for up to two weeks. The bird on the nest does not feed during this period.
Once the chick hatches it is guarded for a few days or for several weeks, depending on the species. By this time it is old enough to be left unattended, and its demands for increasing quantities of food necessitate both parents to forage simultaneously. With some species of albatrosses, petrels and penguins, a week or more can go by before one or other parent returns with food. Meals, though infrequent, can be large; chicks occasionally are fed their own body weight in food in a single meal.
When breeding has finished, most seabirds, especially petrels, disperse widely from their colonies. Some are truly migratory, with all or most of the individuals travelling from New Zealand to distant non-breeding areas. At least eight species of the shearwaters and petrels that breed in New Zealand during spring and summer spend winter in the north Pacific. Four of these – the wedge-tailed shearwater (Puffinus pacificus), black-winged petrel (Pterodroma nigripennis), white-naped petrel (Pterodroma cervicalis) and Kermadec petrel (Pterodroma neglecta) – breed in northern New Zealand and spend winter in the tropical north Pacific. Cook’s petrels (Pterodroma cookii) fly a little further east for winter, to waters off Mexico and California. The remaining four species spend the New Zealand winter in Arctic or subarctic waters.
Buller's shearwaters (Puffinus bulleri), flesh-footed shearwaters (Puffinus carneipes), sooty shearwaters and mottled petrels all finish breeding in April or May, then rapidly fly north to reach the northern Pacific about a month later. Non-breeding birds leave first, and fledglings depart some weeks after their parents. Sooty shearwaters are first seen off Japan in May, in Alaskan waters by June, and off California in August and September, before they begin the return journey to New Zealand.
Black petrels (Procellaria parkinsoni), Chatham petrels (Pterodroma axillaris) and white-faced storm petrels (Pelagodroma marina) spend winter in the eastern tropical Pacific, some as far east as the Galapagos Islands. Most Hutton's shearwaters (Puffinus huttoni) and many New Zealand breeding gannets spend their non-breeding months in Australian seas.
At least 20 of the seabird species which breed in New Zealand are threatened or endangered. There are two main threats:
Every year, a great number and variety of seabirds flock to the predator-free islands of the Chathams group to breed. Crowded alongside each other are three species of albatross, one penguin, three shag and 13 petrel species. Seven of these are endemic (breed nowhere else), including the Chatham Island tāiko (Pterodroma magentae), perhaps the world’s rarest petrel.
Observing seabirds around New Zealand is relatively easy. The best place to see pelagic (open-ocean) birds is offshore Kaikōura; a boat trip of a few kilometres affords sightings of a variety of albatrosses and petrels.
Otago Peninsula is famous for its royal albatrosses and yellow-eyed penguins, and observant visitors will also see several species of shag. Sooty shearwaters and other open-ocean birds can often be seen from the coast. There are accessible gannet colonies at Cape Kidnappers, Muriwai Beach and Farewell Spit. Little penguins can be seen at many places, but Ōamaru in North Otago offers the best viewing opportunities. A variety of shearwaters, prions, albatrosses and other seabirds are usually visible from Cook Strait and Foveaux Strait ferries, and from ferries and other vessels in the Hauraki Gulf. Other seabirds can often be seen close to shore around many parts of New Zealand, but observers may need binoculars to identify them.
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