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Satellite-tracking the flight of the godwit

Wednesday, March 28, 2007

Satellite-tracking the flight of the godwit

As the last bar-tailed godwits leave New Zealand estuaries on their northern migration to Alaska this week, Massey scientists will trace their journey via satellite-tagged individuals.

Dr Phil Battley, an ecologist at the University’s Palmerston North campus, says the shorebirds’ northern migration is of particular interest because the birds touch down in Asia and are potential carriers of the H5N1 bird-flu virus to the Alaskan region.

Dr Battley says that while the 11,000 km southern migration of the godwit from Alaska to New Zealand is thought to be the longest non-stop migration of any bird, not much is known about their northern route.

He is leading the New Zealand component of a collaborative research project with the United States Geological Survey and PRBO Conservation Science in the US to learn more about global migration patterns of declining shorebird species in the Pacific Basin.

With Dr Brett Gartrell, a wildlife veterinarian with the University’s New Zealand Wildlife Health Centre, and veterinarian Dan Mulcahy from the United States Geological Survey, Dr Battley oversaw the tagging of 16 godwits in the Firth of Thames and Golden Bay.

Eight of the birds were fitted with backpack tracking devices, and another eight had devices surgically implanted. Dr Gartrell says the implants are more secure than the backpack harnesses and do not affect the aerodynamics of flight.

The information gathered from the birds’ flight will answer questions about their stops en route and their routes from New Zealand to Alaska. Dr Battley, who has been working on movements and demographics of godwits for the past three years, says the birds have a major stopover in the Yellow Sea region of eastern Asia.

He says three birds have recently landed in the Yellow Sea, with one covering 11,000 km in just over seven and a half days, at an average speed of 56 km/hr.

“This probably qualifies as the longest migratory flight of its type measured in the world. Everything points to this bird having flown from non-stop from New Zealand to China.”

Other birds have stopped in Papua New Guinea, the Southern Philippines and on an island in Micronesia, and the rest are flying towards China or the Korean peninsula.

“They fly in reasonably small flocks of 30 to 70 birds, and if one has touched down somewhere it is probable that a flock has landed.”

The tagging project will also provide crucial information about the migratory behaviour of declining species. Throughout the East Asian and Australasian flyways, 85 per cent of shorebird populations are declining, and 40 per cent of shorebirds inhabiting Oceania are classified as threatened or near threatened.

Godwits arrive in New Zealand in September each year and the adults leave in mid-March, with adolescent birds staying until they are up to three or four years old. They are widely distributed, and the largest populations are found in the Kaipara Harbour, Manukau Harbour and Farewell Spit.

Dr Battley says annual population counts at these major sites show a decline in numbers, the reasons behind for which are not yet known. The increasing reclamation of tidal mud flats in Korea and China and the change in geography due to dams such as the Three Gorges Dam are also impacting heavily on bird life.

“We are entering a critical decade for these birds, so the research is timely and crucial,” he says.

The satellite track of the godwits’ navigation can be viewed online at:
http://www.werc.usgs.gov/sattrack/shorebirds/overall.html and more information on the project is available at http://www.prbo.org/cms/index.php

ENDS

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