Cannon-netting

Forest and Bird, Issue 296, 1 May 2000, Page 25

Cannon-netting

hey gather on the beach at dawn, bearing their nets and cannons, like old-time hunters. The purpose of their expedition is still to capture birds, but in the interests of the birds’ survival not the hunters’. For nearly 20 years, members of the New Zealand Wader Study Group, and its predecessors, have been ‘cannon-netting’ wading birds on northern harbours, to assess the health and migratory patterns of the birds. Their discoveries are unravelling the mysteries of those fantastic journeys undertaken by our migratory birds, to and from the Arctic. Recent discoveries suggest that those journeys of 12,000 kilometres and more are even more fantastic than previously supposed. Godwit from Alaska, for example, probably make the journey down to New Zealand in up to 8 days, flying nonstop. The idea behind the practice of cannonnetting is to capture a sample flock of wading birds as they rest near the top of the tide. Harbours such as Kaipara, Manukau and the Firth of Thames, all near Auckland, are ideal for they have vast areas of mudflats which the birds must leave as the tide rises. Firing a net over a known roost provides a way of capturing birds, allowing them to be measured, weighed, and checked for their sex and likely home

range. The birds are then banded, with rings or tiny flags on the legs, and released to make their migratory journey. Birdwatchers along what is known as the AsiaPacific Flyway may then recognise particular birds from their migratory roosting places around the rim of the Pacific. The practice of banding migratory birds became popular in Britain around The Wash during the 1960s. Now groups in Australia and New Zealand are capturing wild birds and banding them in an effort to trace our birds’ journeys half way round the world. The results are critical when it comes to persuading Asian governments, and others, to leave protected areas as resting places for the birds. Some 12 species of wading birds migrate each southern spring to New Zealand, where they fatten on the rich food supplies in our muddy estuaries and shallow harbours. Then in autumn the birds set out again for their breeding grounds in Alsaka and Siberia. Working with the Shorebird Network of similar groups in Australia, the Pacific and Asia, the New Zealand Wader Study Group has mapped the passage and timing of the birds. They know, for example, which river deltas and marshes are frequented on the flyways by New Zealand birds returning to the Arctic to breed. Godwit, for example,

may take two to three months on their northward migration, feeding on the way. It is their return journey which is undertaken at such a phenomenal speed, with comparatively few birds reported as resting on the way. Working with northern scientists, the New Zealand group is able to identify the different forms of each migratory species, pin-pointing individual birds to their likely place of origin by comparing feather detail. By this method it has been possible to deduce that some of our lesser (or red) knot breed on the New Siberian Islands, north of Siberia.

the teams which support the New Zealand Wader Study Group, based at Miranda Shorebird Centre, near Auckland. In their search for basic data about our migratory wading birds (local and international) the group captures birds for recording purposes, and bands their legs with identification rings. Above, a bird-capture net is laid along the tideline adjacent to a known roosting place where birds gather when driven off the mudflats by a rising tide. The pipe-style cannons are carefully angled to carry the net over the roosting place, and the net is disguised with seashells. The cannon is loaded by study leader Adrain Riegen (above), to carry the leading edge of the net over the birds. When the birds move into the area covered by the net the cannons are fired electronically. Projectiles (below) pull the net up and over the roosting birds. This catch includes godwit and knot, both migrants from Alaska and Siberia. and Bird members are among

irds must be taken from the net to avoid stressing them. The layer of scrim helps. Birds are put in darkened boxes until their details can be recorded. Members of the study group measure, weigh and tag the birds. The godwit (below) bears a ring referring to its recorded details. The white flag on the upper leg helps birdwatchers round the world identify a bird which has spent the summer in New Zealand.