KEY POINTS:
Latest attempts to study the globe-trotting exploits of a New Zealand shorebird have struggled to get off the ground.
The bar-tailed godwit has long fascinated experts with its mammoth travels across the Pacific and Asia to breed in western Alaska.
Researchers implanted tiny transmitters in nine birds before they left mudflats at Miranda on the Thames estuary in March to track their movements.
It was the first time they had used a mix of male and female birds.
But they will get data from no more than two - and possibly none - after one died before reaching Asia, two transmitters were lost over the Yellow Sea and four refused to leave New Zealand.
Miranda Shorebird Centre chairman David Lawrie said that two males had reached their breeding grounds but the transmitters had since stopped working, probably due to battery failure.
Scientists will have to wait until next month to see if the birds made the return journey by identifying them through tags on their legs.
"We are not sure they're going to make it back," said Lawrie.
The study is a repeat of research carried out last year when seven birds - all female - were fitted with transmitters.
One, named E7, stunned scientists worldwide by completing the 11,700km flight from Alaska to Miranda non-stop in eight days.
"They just get up and fly and they just keep going," said Massey University ornithologist Dr Phil Battley. "It's quite remarkable."
Godwits reach New Zealand each September. The adults leave in mid-March, with adolescent birds staying until they are 3 or 4 years old.
Lawrie said there were no plans to repeat the study next year because researchers had learnt what they wanted to about godwits' migratory patterns.
He said the tracking had been important to confirm whether they flew non-stop, or "island hopped" down the Pacific.
They are not the only New Zealand-based species impressing scientists around the world.
The epic flights of the sooty shearwater - better known as the muttonbird - have also been mapped, with the species completing a staggering 74,000km journey across the Pacific Ocean.
Twenty-five mother birds from Codfish Island in the deep south, and eight from Mana Island off the coast of Wellington, were tracked for an average of 262 days.
The study found the birds flew a figure-eight pattern across the Pacific that lasted about 215 days.
