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标题: 5月阅读JJ第35篇鸟类迁移【类似原文】 [打印本页]

作者: berog 时间: 2014-5-12 22:07
标题: 5月阅读JJ第35篇鸟类迁移【类似原文】
今天看5月阅读JJ，看第35个时发现似曾相识，然后在从前的托福阅读中找到了，希望狗主们看看对不对。（高亮的应该是相关段落，黑体字是关键点，鸟不会因为有阳光而得瑟，鸟得瑟是因为到了该迁徙的日子了（托福题目里也有提及），然后就是鸟内置精确生物钟才导致那啥的，隐藏的是译文）
Orientation and Navigation

To South Americans, robins are birds thatfly north every spring. To North Americans, the robins simply vacation in thesouth each winter. Furthermore, they fly to very specific places in SouthAmerica and will often come back to the same trees in North American yards thefollowing spring. The question is not why they would leave the cold of winterso much as how they find their way around. The question perplexed people foryears, until, in the 1950s, a German scientist named Gustave Kramer providedsome answers and, in the process, raised new questions.

Kramer initiated important new kinds ofresearch regarding how animals orient and navigate. Orientation is simplyfacing in the right direction; navigation involves finding ones way from pointA to point B.

Earlyin his research, Kramer found that caged migratory birds became very restless at about the time they wouldnormally have begun migration in the wild. Furthermore, he noticed that as theyfluttered around in the cage, theyoften launched themselves in the direction of their normal migratory route. Hethen set up experiments with caged starlings and found that their orientationwas, in fact, in the proper migratory direction except when the sky wasovercast, at which times there was no clear direction to their restlessmovements. Kramer surmised, therefore, that they were orienting according tothe position of the Sun. To test this idea, he blocked their view of the Sunand used mirrors to change its apparent position. He found that under thesecircumstances, the birds oriented with respect to the new "Sun." Theyseemed to be using the Sun as a compass to determine direction. At the time,this idea seemed preposterous. How could a bird navigate by the Sun when someof us lose our way with road maps? Obviously, more testing was in order.

So, in another set of experiments, Kramerput identical food boxes around the cage, with food in only one of the boxes.The boxes were stationary, and the one containing food was always at the samepoint of the compass. However, its position with respect to the surroundingscould be changed by revolving either the inner cage containing the birds or theouter walls, which served as the background. As long as the birds could see theSun, no matter how their surroundings were altered, they went directly to thecorrect food box. Whether the box appeared in front of the right wall or theleft wall, they showed no signs of confusion. On overcast days, however, thebirds were disoriented and had trouble locating their food box.

Inexperimenting with artificial suns, Kramer made another interesting discovery.If the artificial Sun remained stationary, the birds would shift theirdirection with respect to it at a rate of about 15 degrees per hour, the Sun'srate of movement across the sky. Apparently, the birds were assuming that the"Sun" they saw was moving at that rate. When the real Sun wasvisible, however, the birds maintained a constant direction as it moved acrossthe sky. In other words, they were able to compensate for the Sun's movement. Thismeant that some sort of biological clockwas operating-and a very precise clock at that.

What about birds that migrate at night?Perhaps they navigate by the night sky. To test the idea, caged night-migratingbirds were placed on the floor of a planetarium during their migratory period.A planetarium is essentially a theater with a domelike ceiling onto which anight sky can be projected for any night of the year. When the planetarium skymatched the sky outside, the birds fluttered in the direction of their normalmigration. But when the dome was rotated, the birds changed their direction tomatch the artificial sky. The results clearly indicated that the birds wereorienting according to the stars.

There is accumulating evidence indicating that birdsnavigate by using a wide variety of environmental cues. Other areas underinvestigation include magnetism, landmarks, coastlines, sonar, and even smells.The studies are complicated by the fact that the data are sometimescontradictory and the mechanisms apparently change from time to time. Furthermore,one sensory ability may back up another.

作者: jiangshan940213 时间: 2014-5-12 22:17
楼主好人

作者: yhlsjf 时间: 2014-5-12 22:21
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作者: echo盛夏 时间: 2014-5-12 22:21
楼主好人~顶上去~

作者: FIONA-J 时间: 2014-5-12 22:21
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作者: vincenthe2 时间: 2014-5-12 22:29
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作者: 250495841 时间: 2014-5-12 22:34
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作者: rsw 时间: 2014-5-12 22:39
那啥……刚好之前已经加进JJ了……不过还是谢谢

作者: 步步410 时间: 2014-5-12 22:43
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作者: phorstar 时间: 2014-5-12 22:48
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作者: berog 时间: 2014-5-12 22:48

rsw 发表于 2014-5-12 22:39
那啥……刚好之前已经加进JJ了……不过还是谢谢

整理JJ的都是大好人，万分感谢！

作者: 15256031898 时间: 2014-5-12 22:53
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作者: hanxiaomeizi 时间: 2014-5-12 23:00
太感谢了

作者: Badream 时间: 2014-5-12 23:00
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作者: lrffly 时间: 2014-5-12 23:30

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作者: maestri 时间: 2014-5-12 23:33
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作者: tt_123456 时间: 2014-5-13 08:48
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作者: GracehqMa 时间: 2014-5-13 09:43

作者: jacky123321 时间: 2014-5-13 10:59
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作者: summile 时间: 2014-5-13 11:01
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作者: AgendaChen 时间: 2014-5-13 12:00
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作者: smarters 时间: 2014-5-13 12:32
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作者: jing951026 时间: 2014-5-13 12:38
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作者: lanxiaoshan 时间: 2014-5-15 14:03
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作者: 先森，我累了 时间: 2014-5-15 21:58
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作者: mrxmorris 时间: 2014-5-15 22:18
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作者: psy70211126 时间: 2014-5-15 22:23
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作者: April四月 时间: 2014-5-19 00:41
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作者: 兜宝宝 时间: 2014-5-19 03:41
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作者: hsyhz92 时间: 2014-5-20 10:40
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作者: VictoriaCat1989 时间: 2014-5-22 13:41
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作者: hejing3263 时间: 2014-5-25 17:00
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作者: yuhongkui 时间: 2014-9-10 14:20
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作者: b1tch 时间: 2014-11-17 12:17
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