Arctic terns' flying feat: same as three trips to the Moon

Alister Doyle, Reuters 11 Jan 10;

OSLO (Reuters) - Arctic terns can fly more than 80,000 km (49,700 miles) a year, beating past estimates of the seabirds' record migrations and equivalent to three round trips to the Moon over a lifetime, a study showed Monday.

Tiny tracking devices attached to 11 of the small white birds breeding in Greenland or Iceland showed they flew a far more meandering route than expected on their annual trips to the Antarctic and back, an international team of scientists said.

Already widely reckoned to have the longest migration of any creature, the birds flew an average of 70,900 km in a year, with one clocking up 81,600 km. That was double the 40,000 km often estimated in the past.

And over a tern's lifetime of up to 34 years, the migrations add up to about 2.4 million km -- equivalent to three return trips to the Moon or a dizzying 60 times around the Earth.

"This is a mind-boggling achievement for a bird of just over 100 grams," said Carsten Egevang of the Greenland Institute of Natural Resources and lead author of the study with experts in Denmark, the United States, Britain and Iceland.

"Tracking of Arctic terns...reveals longest animal migration," the scientists wrote in the U.S. journal Proceedings of the National Academy of Sciences. Other birds, such as albatrosses or sooty shearwaters, also have massive migrations.

Terns breed around the Arctic, from Iceland to Alaska, and exploit rich summertime fisheries for shrimp-like krill, other plankton and small fish in both polar regions. They escape freezing dark polar winters with their marathon flights.

Egevang told Reuters that one surprise was that the Greenland and Iceland terns paused for a month or so to stock up on food in the Atlantic on their way south in August. Some birds then flew south past Africa, others close to South America.

On the way back north in April and May, the birds took a long "S"-shaped route up the Atlantic, apparently to use prevailing winds to save energy. Flights from Antarctica to Greenland took about 40 days, an average of 520 km a day.

Small "geolocator" devices, weighing 1.4 grams and attached to the tern's leg, recorded the birds' position daily. The data were then downloaded after the birds were caught on return to their Arctic breeding sites.

The British Antarctic Survey, which developed the geolocators, said they could help track ever smaller birds and help identify "biological hotspots" -- such as the region of the Atlantic north of the Azores where the tern paused to feed.

(Editing by Dominic Evans)

Record Migration: Small Birds Travel 50,000 Miles
livescience.com Yahoo News 11 Jan 10;

Some birds make long treks south during wintertime, but the Artic tern bests them all, flying on average 44,000 miles (70,900 km) on its annual migration from pole to pole, according to a new study.

The shortest journey recorded for the tern was 36,900 miles (59,500 km) and the longest 50,700 miles (81,600 km).

The study confirms what has been supposed for decades - the Arctic tern has the longest annual migration of any animal in the world. When added up over a lifetime, the total journey for the bird is the equivalent of three trips to the moon and back.

The researchers used a tiny instrument, called a geolocator, for tracking Artic tern migration. The device regularly records light intensity, which can be used to generate two geographical positions per day.

While geolocators have helped scientists follow the journeys of larger animals, including geese, albatross, penguins and seals, they have only recently been made small enough to attach to light-weight birds, such has the tern. The researchers fitted geolocators weighing about 1.4 g each to the legs of 60 terns.

The study showed that the Artic tern travels an average of around 44,000 miles roundtrip from Greenland to the Weddell Sea, on the shores of Antarctica, and back to the breeding grounds in Greenland - nearly twice the distance generally cited for tern's annual migration, the researchers say.

It turns out that the birds did not immediately travel south, but spent almost a month at sea in the middle of the North Atlantic Ocean. The researchers believe the birds use this lengthy stop-over as a chance to "fuel-up" with food before continuing on to less fruitful waters farther south.

After this pause, the birds continued their long journey south down the coast of northwest Africa. However, around the Cape Verde Islands - islands off the west coast of Africa, close to Senegal - the birds' behavior surprised the research team again. About half of the birds continued down the coast of Africa, while the other half crossed the Atlantic Ocean to follow a parallel route south down the east coast of South America.

All of the birds spent the northern winter months in Antarctic waters.

Interestingly, on their return journey the birds did not choose the shortest route back to their breeding grounds in Greenland. Instead, they traced out a gigantic 'S' pattern northward through the Atlantic Ocean - a detour of several thousand km compared to a straight line north to their breeding colonies. This indirect route allows the terns to take advantage of the global wind system and to reduce the amount of energy it needs to use on its return journey, said Iain Stenhouse, a co-author of the research paper, published Jan. 11 in the journal Proceedings of the National Academy of Sciences.

"This study on seabird migration has given us an incredibly detailed insight into how long-distance migrants behave at times of the year when it's normally impossible for us to follow them," said Carsten Egevang of the Greenland Institute of Natural Resources, lead author of the paper.

The study was conducted by scientists from the British Antarctic Survey (BAS) in collaboration with researchers from Greenland, Denmark, the United States and Iceland.

Arctic tern's epic journey mapped
Jonathan Amos, BBC News 11 Jan 02;

The Arctic tern's extraordinary pole-to-pole migration has been detailed by an international team of scientists.

The researchers fitted the birds with tiny tracking devices to see precisely which routes the animals took on their 70,000km (43,000 miles) round trip.

The study reveals they fly down either the African or Brazilian coasts but then return in an "S"-shaped path up the middle of the Atlantic Ocean.

The long-distance adventure is described in the US journal PNAS.

"From ringing, we knew where the Arctic tern travelled," said Carsten Egevang of the Greenland Institute of Natural Resources.

"The new thing is that we've now been able to track the bird during a full year of migration, all the way from the breeding grounds to the wintering grounds and back again."

The avian world is known for its great migrations.

Albatrosses, godwits, and sooty shearwaters all undertake epic journeys. But none can quite match the Arctic tern's colossal trip.

Starting in August and September, this small bird - which weighs little more than 100g (3.5oz) - will head away from Greenland with the intention of getting to the Weddell Sea, on the shores of Antarctica.

It will spend about four or five months in the deep south before heading back to the far north, arriving home in May or June.

A team from Greenland, Denmark, the US, the UK and Iceland attached small (1.4g/0.05oz) "geolocators" to the animals to find out exactly where they went on this polar round trip.

The devices record light intensity. This gives an estimate of the local day length, and the times of sunrise and sunset; and from this information it is possible to work out a geographical position of the birds.

The geolocators were provided by the British Antarctic Survey (BAS).

"The use of these devices on seabirds is not only revolutionising our understanding of migration patterns, but the resulting data on distribution also help address the requirement to identify important biological hotspots," said Richard Phillips from BAS, a co-author of the PNAS paper.

The first surprise is that the terns do not make straight for the Antarctic when they leave the Arctic, but make a lengthy stop-over in the middle of the North Atlantic, about 1,000km (620 miles) north of the Azores.

Here, they feed on zooplankton and fish to fuel themselves for the long journey ahead.

"We were able to compare biological productivity in the ocean from satellite imagery and we could see a high productive area that the birds will spend time in," said Mr Egevang.

"Even more importantly, it's the last high productive area before they enter tropical waters where we know productivity is low."

The birds then head south along the coast of western Europe and western Africa before making a choice, either to continue hugging Africa or sweep across the Atlantic from the Cape Verde Islands to continue the journey along the Brazilian coast.

About half the birds that were tracked decided to take the South American path. It is not clear why, but the researchers believe wind might make either route seem favourable to the terns.

After spending their northern winter months in Antarctic waters, the terns then fly back towards the Arctic.

But rather than retracing their southward flight paths, the birds follow a gigantic "S" pattern up the middle of the Atlantic Ocean.

"This is completely new knowledge," Mr Egevang told BBC News.

"They make a detour of several thousand km but once we start comparing the route to the prevailing wind system, it makes perfect sense - moving in a counter-clockwise direction in the Southern Hemisphere, and clockwise in the Northern Hemisphere.

"It's just more energy-efficient for them to do that even though they are travelling several thousand more km than if they flew in a straight line."