As well as migrants to and from New Zealand, there are bird species that migrate within the country from one region to another. The estuaries and coastal sites that feed so many international wader visitors through the summer are used in winter by similar numbers of New Zealand waders that breed in other parts of the country. Most of these waders and other species are able to both breed and winter over in New Zealand because of the temperate climate and the diverse habitats, which offer suitable breeding environments as well as concentrated winter feeding grounds.
The native South Island pied oystercatcher is the most numerous internal migratory bird. After breeding on South Island riverbeds, farmland and coasts, the majority of the population of 112,000 assembles at North Island wintering sites. The less common variable oystercatcher, which is endemic (found only in New Zealand), tends to move more locally.
The pied stilt, thought to have colonised New Zealand around 1800, now numbers about 30,000 birds. Most migrate from breeding grounds on riverbeds of the South Island and southern North Island, to northern harbours. Others breed on the coast and are less migratory. The endemic black stilt, of which there are fewer than 200 in the wild, tends to move to sites close to its breeding grounds after it has raised its young.
Most banded dotterels that have not flown to Australia for the winter move to coastal and estuarine sites around New Zealand. Others remain on river deltas and pastureland through winter. The rare endemic New Zealand dotterel has two subspecies. The 2,200 or so northern birds mainly stay year-round near their breeding sites. The scarcer southern birds are now confined when breeding to Stewart Island, with numbers hovering around 260. They breed on summits above the bush line but move to coastal wintering sites, including the Southland coast.
The small endemic wrybilled plover, ngutuparore, breeds on braided rivers near the Southern Alps, then flies to tidal harbours in the North Island or the north of the South Island. This species is notable for being the only bird in the world with a sideways bend to its bill. It has a population of 5,000.
Gulls and kingfishers
The endemic black-billed gull breeds on braided riverbeds and other inland sites, and it moves to coastal sites for winter.
Some kingfishers (kōtare) breed around coasts and estuaries, while others breed at inland sites. Those that breed at high altitude tend to move to lower land in winter.
Songbird species, such as starlings, blackbirds and thrushes that move long distances in the northern hemisphere abandoned migration when introduced to the more temperate New Zealand climate. Introduced ducks and geese also stopped migrating, although some move seasonally between breeding grounds and aquatic areas.
One native songbird that could be considered migratory is the silvereye or tauhou, which is a relatively recent colonist from Tasmania. After the breeding season they form flocks and move around the country. The Tasmanian population of the same sub-species migrates to Queensland.