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© Wikimedia CommonsThe short-tailed shearwater
Nearly 200 seabirds have been found dead along Waikato's west coast beaches.

A total of 184 short-tailed shearwater, a migratory bird that typically breeds on the islands between Tasmania and Victoria, have been washed ashore between Waikorea beach and Taharoa, south of Kawhia.

It is not known when the birds died and were washed ashore, but numbers are said to be "unusually large" by one expert.

Hugh Clifford, who organised the beach patrol on behalf of the Waikato branch of the Ornithological Society, said the number of short-tailed shearwater found this year was much higher than normal.

"There would be millions of them passing down through the Tasman Sea on the southern migration.

"Some of them were pushed closer to New Zealand and the food conditions may have been unfavourable, causing them to perish."

Each year during the southern hemisphere winter, the short-tailed shearwater migrate about 15,000 km to the Northern Pacific, before making their way back towards southern Australia to breed around October.

Mr Clifford said when a large number of birds are found dead along the coast, it is called a "wreck".

The beach patrols, which took place at Waikorea, Taharoa, Ruapuke and Kawhia, found an average of seven birds for each kilometre walked.

The number of short-tailed shearwater found this year is the highest in more than a decade and dwarfs tallies recorded in previous years.

In 2012, the Waikato beach patrols found only eight short-tailed shearwater among 344 dead seabirds.

Dr Graeme Taylor, a principal science advisor at the Department of Conservation, said a wreck was usually the result of strong onshore winds and poor feeding conditions.

"Onshore winds will drive the birds towards the coast and as a result the weakened birds will fight to try to get back towards the ocean, but lose the battle."

The exhausted birds plunged into the sea and were then washed ashore dead.

Dr Taylor said poor feeding conditions in the North Pacific could also play a part.

"They don't eat anything in migration. They basically fatten up in the North Pacific before they come south."

In 2011, 29,934 seabirds were found strewn along Waikato's coast - part of the largest wreck in more than a decade.