Waders and Other Migrants
Migratory birds fall into several categories, the best known being birds breeding in the Siberian and North American Arctic, mainly members of the order of birds commonly known as waders. The principal Northern Hemisphere migrants spending the summer in New Zealand are the bar-tailed godwit (Limosa lapponica), knot (Calidris canutus), turnstone (Arenaria interpres), and Pacific golden plover (Charadrius dominicus). In addition there are a certain number of rarer species and stragglers. The feeding grounds of these migrants, in the summer months from approximately September to March, are the extensive tidal mudflats of harbours and estuaries and shallow margins of brackish lagoons. An interesting feature of the annual migration is that a certain number, probably comprising mainly immature birds, remain to spend the winter in New Zealand; however, these form only a small portion of the birds that yearly make the trans equatorial migration.
The Arctic skua, mentioned under “Sea Birds”, also reaches New Zealand as a migrant from the Northern Hemisphere.
There is a notable trans equatorial migration that forms a second category, as this is performed by species breeding in the New Zealand area. These birds are the three larger species of shearwater: the sooty shearwater or New Zealand muttonbird (Puffinus griseus), flesh-footed shearwater (Puffinus carneipes), and Buller's shearwater (Puffinus bulleri). These are largely absent from the seas surrounding New Zealand between the termination of breeding in May to October; their migration takes them to the north and east Pacific.
The only other group of overseas migrants comprises the two species of cuckoo already mentioned, which depart at the end of the summer for islands of the tropical Pacific. Migrants across the Tasman Sea to Australia are described below.
Local migration is well developed, once again mainly amongst the waders – the South Island pied oystercatcher (Haematopus ostralegus finschi), banded dotterel (Charadrius bicinctus), wrybill (Anarhynchus frontalis), and pied stilt (Himantopus himantopus). The most pronounced migration is that of the unique wrybill, the only species in the world with a bent bill; it breeds only on the open beds of eastern South Island rivers, migrating to the tidal harbours of the Auckland area. The remaining species mentioned have only a partial northwards migration, numbers spending the winter in southern districts; further, an additional migration in an east-west direction is performed by a proportion of the population of banded dotterels which cross the Tasman Sea annually to Australia in considerable numbers. By means of banding, local and trans-Tasman migrations are now being investigated by the Ornithological Society of New Zealand.
Of waterfowl, the grey duck is probably a local migrant and is known to travel to Australia and the Chatham Islands. The white-fronted tern is a partial migrant to eastern Australia; and there is a local migration, also partial, of black-fronted terns to the southern and central North Island. It has been shown recently by systematic banding that young gannets from the New Zealand colonies nearly all migrate to Australian waters.