Temperate feeding grounds
New Zealand has plenty to offer migrating birds in their non-breeding season. Some inshore- and offshore-foraging seabirds that breed in the far north or far south take respite in the milder conditions around New Zealand. To waders, New Zealand’s 300 estuaries (a total area of 100,000 hectares of estuaries and coastal mudflats) provide highly productive feeding grounds for tens of thousands of migrants during the southern summer. The fact that New Zealand was free of predators such as stoats, cats and dogs until relatively recently was another advantage. Among the most important sites are the Kaipara Harbour, Manukau Harbour, the Firth of Thames, Farewell Spit, Golden Bay, the Avon–Heathcote Estuary and Lake Ellesmere.
Most of the Arctic waders travel to and from New Zealand via the western edge of the Pacific, on the East Asian–Australasian Flyway, making coastal stopovers to rest and feed along the way. The staging sites are vital for the birds to be able to continue their journeys and return home to breed again.
Pressure from expanding human populations at many sites (some of which are adjacent to huge cities) has led to a steady deterioration of the birds’ habitat. A combination of housing and industrial development, pollution, land reclamation on mudflats, changes to water flows and increased risk from predators at these stopping points has meant that fewer birds can feed and rest before the next stage of the journey. The result has been a decline in bird populations.
Conservation across national boundaries
Several international organisations have attempted to protect some waders’ habitats along the course of flyways such as the East Asian–Australasian Flyway. By 2006, six New Zealand sites were included in the Ramsar Convention as Wetlands of International Importance: the Firth of Thames, Kopuatai Peat Dome, Whangamarino, Manawatū Estuary, Farewell Spit, and Waituna Lagoon.
Migratory waders that arrive and form large flocks at feeding sites through the southern summer include 90,000 bar-tailed godwits, 35,000 lesser knots and 5,000 ruddy turnstones. Another half-dozen wader species are regular visitors (50–700 birds). These include the Pacific golden plover, the red-necked stint, the whimbrel and the sharp-tailed sandpiper. A further dozen or more wader species are occasional visitors, along with other rarer travellers that have strayed from their usual route.
Before Polynesian voyagers set off to explore the Pacific, the sight of godwits flying south through the central Pacific gave them a clue that land lay to the south – Aotearoa (New Zealand).
Eastern bar-tailed godwits
At least one exceptional long-distance migrant makes the journey from the Arctic without any stopovers. The eastern bar-tailed godwit makes a record-breaking non-stop flight over the Pacific Ocean from Alaska to New Zealand. This journey of 11,000 kilometres takes eight or nine days and nights of continuous flight, averaging about 56 kilometres per hour. The departure is timed to gain assistance from favourable winds. The birds arrive exhausted and weighing less than half their original weight. They remain for around five months before making the return journey along the western edge of the Pacific.
Skuas are gull-like birds that steal other birds’ food, eggs and chicks. Skuas of both hemispheres visit New Zealand waters. The Arctic skua, the less common Pomarine skua and the long-tailed skua come south in the southern summer. The South Polar skua and subantarctic skua move north during the southern winter.
So far from home
A tiny Arctic tern found at Mason Bay, Stewart Island, in December 2003 had been banded five months earlier as a chick in Hälsingland, Sweden. It must have flown down the Atlantic and across the southern Indian Ocean and Tasman Sea – an estimated 25,000 kilometres.
Several species of tern migrate to New Zealand each year in small numbers. These include the common tern and the Arctic tern, both from the Arctic region, and the little tern and the white-winged black tern from Asia. Some of these mix with flocks of New Zealand’s native white-fronted terns.