Some of the tens of thousands of migratory shorebirds now returning to New Zealand after the summer breeding season in the Northern Hemisphere have a secret that researchers are keen to unravel.
The latest thinking among ornithologists is that bar-tailed godwits from Alaska make the journey nonstop, a distance of about 11,000km.
There is no firm evidence that the birds do fly without stopping over a distance farther than a passenger jet can fly without refuelling, but the suspicion that they do is high.
One of the world's foremost experts on migratory birds, Dr Theunis Piersma, of the Netherlands, is in New Zealand to meet colleagues and attend a welcoming ceremony for the birds at the Miranda Shorebird Centre, on the west coast of the Firth of Thames, on Sunday.
Dr Piersma says if it can be proven that the Alaskan birds fly here nonstop, New Zealand would be one of the world's most important migratory shorebird destinations because of the importance of the feat.
While godwits and knots from Siberia make one or two stops for feeding in their month-long journey to our shores, the birds from Alaska are thought to fly their route in seven to 10 days.
Dr Piersma says it is possible for the birds to make the journey, based on their body weight, energy consumption, the wind patterns they will encounter and the speed they fly.
But the feat is at the extreme end of their survivability.
The likelihood of researchers witnessing individuals arriving is remote. Dr Piersma says the world is too big and the birds too small. It would be impossible for a birdwatcher to detect a bird leaving Alaska and another to see the same bird arriving in New Zealand days later.
Satellite tags of the sort used on albatrosses are no use because the godwits are too small to be fitted with them. But they might be able to carry radio-transmitting tags so their movements can be tracked.
Dr Piersma has already been to Parengarenga Harbour, in Northland. He says the newly arrived birds, possibly from Alaska, were much thinner than those at Miranda, the destination for many flagged or banded birds migrating from Siberia.
Dr Piersma has been campaigning for New Zealand to safeguard its food stocks - creatures such as molluscs or worms - for the birds.
In Europe and the United States, shellfish harvesting has cut migratory shorebird bird populations. He is concerned that, if approved, mussel spat farms covering more than 10 sq km of water near Miranda could result in mussels replacing the marine life the birds feed on.
"If you value these shorebird populations as a nation it seems logical to me you first do a proper ecological investigation into the potential impacts of these farms and then decide what you should do."
And - because so many environmental conditions have to be just right for the birds to survive their long flights - he believes their arrival should be celebrated.
"They are an extremely good omen and something to be cherished."
While a number of welcomes around the country mark the birds' return - and the onset of spring - there are no festivals in Auckland on the scale of those at migratory bird centres overseas or Dunedin's spring celebration marking the return of royal albatrosses to breed at Taiaroa Head.
Dr Piersma will speak at Miranda on Sunday. The welcome begins at 10 am.
Links
Miranda Shorebird Centre
Feather-power's secret - an 11,000km record
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