Spot shags spitting stones on shore before sunrise

The first light of a winter dawn brings a natural spectacle to Golden Bay's Tata Beach.

Hundreds of shags from one of New Zealand's largest spotted shag colony, on the Tata Islands 1000 metres offshore, fly to the beach to congregate in one long mass along the shoreline.

These gregarious birds, some 70 centimetres tall, stand still for a while before flapping their wings and diving into the shallows to swallow pebbles which they then regurgitate in piles on the beach.

By sunrise they fly off, sometimes in groups, out to sea to swim and dive for fish. All that remains of their presence are hundreds of piles of little stones, mixed with the odd shell or shard of weathered glass.

When The Nelson Mail headed out before dawn yesterday to witness the phenomenon, the only other human being on the beach was retired GP Helen Kingston, a Ligar Bay resident who is one of a small number of volunteers documenting the birds for a survey. "It's an amazing spectacle and the beauty of Tata is that it's accessible," she said.

What made yesterday even more spectacular was the setting, with the surrounding mountains covered with snow down to 100 metes above sea level.

The survey started three years ago, following a suggestion by Forest and Bird ornithologist Ann Graeme to count the birds and monitor their behaviour. On survey days, about three a month this winter, volunteers have counted between 500 to 1000 birds a day. Yesterday Dr Kingston counted 712 shags, much less than typically seen last year. On one day in June last year there were 5000 shags, the greatest number ever recorded.

Spotted shags inhabit the crevices and fissures of the Tata Island cliffs all year, but only in winter do they congregate in such large numbers on the beach.

Scientists don't really know why, Dr Kingston said. One theory is that the birds need to ingest stones to cleanse their guts of parasitic worms. The coarse sand at Tata may provide just the right sized pebbles, unlike the finer sand at other nearby beaches.

"The stones ingested are about 1cm wide but you sometimes see big ones of 3cm," she said.

Reasons for this year's drop in shag numbers could be due to a declining food supply, Dr Kingston believed.

The shags from Tata Islands also congregate in lesser numbers on beaches in Abel Tasman National Park. People considering getting up at the crack of dawn to watch Golden Bay's wildlife spectacle should stay up above the high-tide line and keep low to avoid disturbing the birds, Dr Kingston said.

Dogs are banned from the beach in winter for one hour before and one hour after sunset.

Golden Bay Conservation Department ranger Mike Ogle said the national population of spotted shags was between 10,000 to 50,000, of which about 1200 are on the Tata Islands.

The Nelson Mail