Foraging while breeding
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.