2009-12-10 00:55:49frank
猛禽穿越撒哈拉沙漠的季節性遷徙
多虧了GPS技術與其定位裝置的進步，科學家得以一窺侯鳥遷徙的秘密。
瑞典的科學家在魚鷹(ospray)、雕頭鷹(honey buzzard)及其他猛禽身上裝衛星定位器，成功的收集到了九十個穿越撒哈拉來往於瑞典與西非間的季節性侯鳥遷徙記錄。這些記錄透露了這些季節性的猛禽遷徙的一些線索，及可貴的資訊。
猛禽在春秋兩季遷徙於西非與瑞典間，飛行距離約維一千英哩，需要飛行六天半。未成年的鳥第一次這種長程飛行死亡率高達三分之一，成年的死亡率就只有２％。在40%的遷徙飛行次數裡，這些鳥類出現了奇怪的行為：速度慢下來、停下來甚至改變路線、有些甚至在原地繞圈、或飛回他們原本起飛的地方。
用口袋裡的相機拍的魚鷹，在藍天的背景下只能看到兩個小小的剪影。by Frank 2009.10.31 新店廣興
瑞典的科學家在魚鷹(ospray)、雕頭鷹(honey buzzard)及其他猛禽身上裝衛星定位器，成功的收集到了九十個穿越撒哈拉來往於瑞典與西非間的季節性侯鳥遷徙記錄。這些記錄透露了這些季節性的猛禽遷徙的一些線索，及可貴的資訊。
猛禽在春秋兩季遷徙於西非與瑞典間，飛行距離約維一千英哩，需要飛行六天半。未成年的鳥第一次這種長程飛行死亡率高達三分之一，成年的死亡率就只有２％。在40%的遷徙飛行次數裡，這些鳥類出現了奇怪的行為：速度慢下來、停下來甚至改變路線、有些甚至在原地繞圈、或飛回他們原本起飛的地方。
用口袋裡的相機拍的魚鷹，在藍天的背景下只能看到兩個小小的剪影。by Frank 2009.10.31 新店廣興
Observatory
Clues to What Birds Do on a Trans-Sahara Trip
By HENRY FOUNTAIN
December 8, 2009
Nobody ever said migrating thousands of miles through the air twice a year was easy. But few detailed studies have been conducted on just how difficult bird migration can be. That is because birds are tough to track; conventional techniques like banding can provide only limited information about their travels.
But technology has ridden to the rescue, in the form of small satellite tags. Tags that can gather GPS data and transmit it to a satellite are getting so tiny — the puniest are on the order of one-third of an ounce, including the battery — that they can now be attached to large birds to track their travel over long distances.
Scientists in Sweden have done this, and have gained some valuable information about how raptors cope with migrating across the Sahara, between Sweden and West Africa, in spring and fall. In short, it’s a very rough journey.
Roine Strandberg and Raymond H. G. Klaassen of Lund University and colleagues tracked 90 trans-Sahara flights by juvenile and adult ospreys, honey buzzards and other raptors. As reported in Biology Letters, the mean distance traveled, from one edge of the desert to the other, was about 1,000 miles. Mean travel time was six and a half days.
The researchers found that in 40 percent of the flights, there was evidence of odd behavior — the birds slowed down, stopped for an hour or more, changed course or, in some cases, turned around and headed back where they came from. The researchers suggest that strong headwinds or dust storms were responsible.
Deaths also occurred, particularly among juveniles. About one in three young birds died on their first trip. “That’s much higher than we expected,” Dr. Klaassen said.
Adult mortality was only about 2 percent, the researchers said, but adults faced a different problem: those that were delayed by weather had less breeding success than those who made it to the nest on time.
“They only have a good summer if they make the crossing in one attempt,” Dr. Klaassen said. “If they have to stop or turn back, there’s a big risk they won’t have breeding success.”
Copyright 2009 The New York Times Company
http://www.nytimes.com/2009/12/08/science/08obtrip.html?ref=science
The story was taken from The New York Times. Copyright belongs to The New York Times Company. The author of this story and The New York Times are not involved with, nor endorse the production of this blog.
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