一隻小小的鳥兒(約100g+)，竟然一年可以遷徙飛行七萬公里。多虧衛星追蹤器的不斷精進。以下這個圖也是BBC的報導中所引用的照片，科學家所用的Geolocator.
科學家也很驚訝的發現遷徙的路線不是直線而是Ｓ行的。我想這應該跟地球自轉的信風有關，以下的圖是在網路上找到的，也是以前高中自然地理課本裡所用的圖：地球的行星風系。往南的遷徙要飛34,600公里，往北的遷徙距離就短了許多，但是也長達25,700公里，相差8,900公里。
Arctic tern's epic journey mapped
By Jonathan Amos
Science correspondent, BBC News
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 seeprecisely which routes the animals took on their 70,000km (43,000miles) 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 ofthe 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.
After setting out (yellow line) the birds pause in the North Atlantic(red circle) to feed. Going home (orange line), they follow the winds
Total distance travelled 70,900km On southbound leg: 34,600km Daily progress south: 330km On northbound leg: 25,700km Daily progress north: 520km Within Winter grounds: 10,900km "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 epicjourneys. But none can quite match the Arctic tern's colossal trip.
godwit n. 鷸
sooty adj. 1. covered with soot沾滿煤煙子的
2. of the colour of soot煤煙子一樣黑的；炭黑色的
shearwater n. 【動】海鷗
Starting in August and September, this small bird -which weighs little more than 100g (3.5oz) - will head away fromGreenland with the intention of getting to the Weddell Sea, on theshores of Antarctica.
It will spend about four or five months in the deepsouth before heading back to the far north, arriving home in May orJune.
A team from Greenland, Denmark, the US, the UK andIceland attached small (1.4g/0.05oz) "geolocators" to the animals tofind out exactly where they went on this polar round trip.
The devices record light intensity. This gives anestimate of the local day length, and the times of sunrise and sunset;and from this information it is possible to work out a geographicalposition 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 ondistribution also help address the requirement to identify important biological hotspots," said Richard Phillips from BAS, a co-author ofthe PNAS paper.
The first surprise is that the terns do not make straight for theAntarctic when they leave the Arctic, but make a lengthy stop-over inthe 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.
zooplankton n. 浮游動物
"We were able to compare biological productivity in the ocean fromsatellite imagery and we could see a high productive area that thebirds will spend time in," said Mr Egevang.
"Even more importantly, it's the last high productivearea before they enter tropical waters where we know productivity islow."
THE LONG DISTANCE FLIER
Scientific name: Sterna paradisaea Average wingspan of 75-85cm Breeds in Arctic and sub-Arctic Lays eggs in small ground scrape Feeds on fish and crustaceans Birds live more than 30 years 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 thejourney along the Brazilian coast.
About half the birds that were tracked decided to takethe South American path. It is not clear why, but the researchersbelieve 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 birdsfollow 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 comparingthe 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 thateven though they are travelling several thousand more km than if theyflew in a straight line."
Jonathan.Amos-INTERNET@bbc.co.uk
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/8451908.stm
Published: 2010/01/11 23:53:41 GMT
© BBC MMX
The story was taken from the website of BBC news. The copyright remains with BBC. The author of the story and BBC are not involved with, nor endorse the production of this blog.
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