Satellite tracking the Bar-tailed godwit's massive migration from New Zealand to Alaska

02/11/2006 00:00:00 As the last bar-tailed godwits leave New Zealand estuaries on their northern migration to Alaska, Massey scientists will trace their journey using satellite-tagging. 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 four birds have recently landed in the Yellow Sea, all covering more than 10,000 km in six and a half to seven and a half days.

‘These make godwits as arguably the champion migrants of the bird world. Everything points to these birds having flown from non-stop from New Zealand to China and Korea.’

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 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