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 NavigationTo 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.
参考译文：
定位和导航
在南美，知更鸟每年春天都会飞往北方。而在北美，知更鸟每个冬天又都会往南飞。而且，他们会飞往几个固定的位于南美的地方，然后在第二年春年又会回到在北美原来的那些树上。问题是他们为什么会在寒冷的冬天离开，然后又是怎样找到迁徙的路径的。这个问题困扰了人们很久，直到1950年，一个叫做Gustave Kramer 的德国科学家回答了这个问题。但同时，又提出新的问题。
Kramer提出了新的重要的关于动物如何定位和航行的研究。定位就是面朝正确的方向，航行包括了找到从A点到B点的路径。
在这些研究的早期，Kramer发现被关在笼子里有迁徙习惯的鸟在他们往常在野外应该开始迁徙的时候变得好动。而且，他注意到，当这些鸟在笼子里躁动不安时，他们通常将自己推向通常的迁徙路径的方向。他于是将星椋鸟关在笼子里做实验，然后发现了他们的方向。事实上，他们有在适当的迁徙方向，除了天空布满云彩德时候，因为这个时候往往使得他们的骚动不安的活动没有了清楚地方向指向。因此，Kramer猜测道，他们时通过太阳的方位来确定方向的。为了验证这个猜想，他蒙住他们的眼睛并且用镜子改变太阳的自然方位。他发现，在这种环境下，这些鸟按照新的太阳来定位。似乎他们把太阳作为一个罗盘来决定他们的方向。在那个时候，这种猜想看上去是荒谬的，当我们中的一些在有地图的情况下都会走失他们又怎么能够用太阳进行导航呢？显而易见的，接下来会有更多的实验。
所以，在另外一组试验中，Kramer在鸟笼周围放置了相同的餐盒，但是只有一个餐盒中有食物。这些餐盒是静止的，装有食物的那个餐盒始终在罗盘的同一个地点。但是，这个点会由于周围的环境而发生相对改变，那就是既可以通过旋转装有鸟的内部笼子或者旋转作为背景的外墙。只要这些鸟可以看见太阳，无论他们身处的环境如何变化，他们都为径直找到那个正确的餐盒。无论这些盒子是在左墙还是右墙前方，他们都没有表现出迷惑的样子。但是，在阴天，他们就不能定位并且有困难发现盛有食物的餐盒。
在关于人造太阳的试验中，Kramer又有一些有意思的法相。如果人工太阳保持静止，这些鸟会每小时以15°的速度去改变他们的方向，这个速度正是太阳在天空中运动的速度。显然，这些鸟认为他们所看见的“太阳”是按照这个速度移动的。但是，当看见真正的太阳时，这些鸟保持了连贯的方向，正如太阳在天空中移动一样。也就是说，他们可以适应太阳的运动。这就意味着，有一种非常精准的生物钟在起着作用。
那些在夜晚迁徙的鸟又是怎样的呢？也许他们通过夜晚的天空来航行。为了验证这个猜想，这些在夜晚迁徙的鸟被关进笼子里，并在他们的迁徙期放置在一个天文馆里。这个天文馆是一个具有穹顶状的天花板的剧场，并且这些天花板可以放映出一年中任何夜晚的样子。当天文馆的屋顶与外面的天空相吻合时，这些鸟就会朝着往常迁徙的方向振翅。但是当这个圆屋顶旋转的时候，这些鸟改变方向以适应这个人造天空。这就清楚地表明这些鸟是通过星星来进行方向定位的。
这些不断积累的证据表明鸟是通过非常多的外界环境信息来引导他们的航行的。包括磁场、里程碑、海岸性、声波甚至气味也同样被作为实验对象进行观察。由于这些数据常常是相反的并且磁场经常随着时间的改变而改变的事实，使得这些研究非常的复杂。此外，一种知觉能力可能会支持另一种。
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发表于 2014-5-12 22:07:55
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