The Firth of Thames, with its 8,500 ha of wide inter-tidal flats, attracts thousands of migratory wading birds.

Some make the arduous 10,000 km journey south from the Arctic circle to arrive in the spring and fly north again in the autumn; others fly 1,000 km north from the braided river systems of the South Island in the autumn and return in the spring.

In October it's a changing of the guard as the arctic migrants like the eastern bar-tailed godwit, the turnstone and the red necked stint arrive and the birds from the South Island like the wrybill, South Island pied oystercatcher and the kōtuku which have over-wintered in the Firth, fly back to their southern breeding grounds.

A welcome ceremony, organised by the Miranda Naturalists Trust, is held in mid-October. In mid-March another ceremony marks the autumn change-over as the godwits, the turnstones, the stints and others head off and the birds from the south move in.

Favoured destination

The shellbanks which have formed along the coast provide safe roosting for birds at high tide and make for easy bird viewing. Miranda is listed as internationally important under the International Union for Conservation of Nature and Nature Resources Ramsar Convention. The tidal mudflats of the Manukau Harbour are another favoured destination for migratory birds. Auckland International Airport has had to make allowances for the flight paths of these waders.

Hazardous journeys

The tidal flats and mangroves between Miranda and Thames support up to 40,000 birds. Sixty different species have been recorded, 24 of them wading birds. The Ornithological Society conducts a census in November and June. Which species, and how many of them, find their way to the Firth each year?

It is not just wind, weather and the huge distances they have to contend with. A million arctic migrants are shot for food each year as they travel via the East Asia-Australasian flyway, and more and more of their vital tidal mudflat stopovers are being reclaimed for airports or other building developments.

Banding birds for answers

The godwits are the most common arctic wader to arrive. They make only one stopover of up to three weeks halfway on the journey at mudflats in Japan, the Phillipines, Thailand, Malaysia or Bangladesh. There they double their normal bodyweight for the next 5,000 km leg of the journey.

The tiny red-necked stints are the smallest. Weighing in at just 30 g, they are as light as a sparrow. And arctic terns, the champions of the arctic migrants, may travel up to one million km during a 30-year lifetime. These terns are occasionally seen on the mainland on their way to and from the Poles.

The ability of birds to migrate from one part of the world to another has always fascinated people. Why and how do they do it and which routes do they take? A banding programme is carried out over the summer by volunteers with the New Zealand Wader Study Group to find out just where the birds at Miranda go on their way to and from the arctic circle. Nets are used to capture birds as they rest at Miranda's high tide roosts and a small white plastic flag is attached with a band to the upper leg. This lets people in other places know these birds have come from New Zealand.

As reports of sightings come in, a more complete picture of their perilous journeys can be put together, along with statistics to help persuade foreign governments to preserve essential mid-journey habitats. Tiny transmitters are put on some of the larger waders like the curlews. The programme is organised by Miranda Naturalists Trust member Adrian Riegen.