首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The annals of natural history contain many astonishing examples of the ability of animals to find their way home after making di
The annals of natural history contain many astonishing examples of the ability of animals to find their way home after making di
admin
2011-02-05
38
问题
The annals of natural history contain many astonishing examples of the ability of animals to find their way home after making distant journeys. Salmon, for example, are born in freshwater streams and soon afterward journey down to sea. Several years later, after they have attained maturity, they swim back upstream to spawn and, in many cases, to die. The particular stream that serves as the journey’s end is almost invariably the same one in which they were born. It is chosen out of dozens or hundreds of equally suitable streams. The expression "almost invariably" is used advisedly in this case. In one investigation by Canadian biologists, 469,326 young sockeye salmon were marked in a tributary of the Fraser River. Several years later almost 11,000 were recovered after they had completed a return journey to the very same stream, but not a single one was ever recovered from other streams nearby. What underwater guideposts can these fish possibly follow? It has been discovered by A. D. Hasler and his associates at the University of Wisconsin that the salmon, like many other fish, have an acute sense of smell and are able tore member slight differences in the chemical composition of water. The most reasonable theory to explain salmon homing is that each individual remembers the distinctive "fragrance" of its native stream. As it moves upstream it makes the correct choice each time a new tributary is encountered, until finally it arrives home.
Long-distance migration is especially common in birds, because many species must make annual journeys between their nesting grounds and prime feeding areas far away. Each year over 100,000 sooty terns, an attractive tropical sea bird, travel from the waters off the west coast of Africa all the way across the Atlantic to Bush Key, a tiny island near the tip of Florida. Here they build their nests and breed. Once the young can fly, all journey back over the Atlantic. Why do the sooty terns migrate at all? Like many other seabirds, they find protection from cats, foxes, and other predators on isolated islands. It is evidently safer for them to make an entire transoceanic voyage to reach one such haven than it would be to try to nest on the nearby African shores. A somewhat different reason lies behind the north-south migration of birds in the temperate zones. Each spring a legion of migratory forms, from robins, thrushes, and warblers to geese and ducks, makes its way north into the greening countryside, where large quantities of food are becoming freshly available. Working rapidly, they are able to rear one or more broods of young. As winter approaches and the food supply declines, all head south again. Some species proceed all the way to Central and South America. The record annual journey in the Western Hemisphere is made by the golden plover, one group of which travels from northern Canada to southern South America. A second group of the same species migrates from Alaska to Hawaii and the Marquesas Islands. Human beings could never make such journeys unaided by maps and navigational instruments. How do the birds do it? A large part of the answer lies in their ability to use celestial clues. At migration time, caged starlings become unusually restless. If permitted to see the sun, they begin to fly toward the side of the cage that lies in the direction of their normal migration route. However, when the sky is overcast and the sun is obscured from view, their movements persist, but they are non directional. Other migratory birds fly at night and can evidently use the position of the stars to guide them. This surprising fact has been established by several biologists, including S. T. Emlen of Cornell University, who allowed a type of bird called indigo buntings to attempt flights under the artificial night sky of a planetarium. The birds oriented "correctly" with reference to the planetarium sky even when the positions of its constellations did not correspond with the position of the true constellations outside. Thus other outside influences were eliminated, and it could be concluded that the birds were able to orient to what they believed to be the position of the stars.
SUMMARY:
Animals are able to get back home after they make long journeys. Salmon, for example, are known to swim back several years later to【51】where they were born. What guide these fish upstream.9 According to scientists at the University of Wisconsin, salmon【52】and follow the fragrance of their native stream as they have a sharp【53】
Birds also make long distance migration each year. Sooty terns, a type of tropical sea bird, travel across the Atlantic from Africa to an island near Florida, where they breed and can【54】from predators. Birds also migrate in order to find food and rear their young. It is discovered that birds are aided by【55】to make distant journeys that even human beings cannot make without the assistance of navigational instruments.
选项
答案
celestial clues/position of the stars
解析
(文章第二段提到How do the birds do it? A large part of the answer lies in their ability to use celestial clues. 因而摘要中可以归纳为celestial clues。)
转载请注明原文地址:https://kaotiyun.com/show/4WAK777K
本试题收录于:
B类竞赛(英语专业本科专科)题库大学生英语竞赛(NECCS)分类
0
B类竞赛(英语专业本科专科)
大学生英语竞赛(NECCS)
相关试题推荐
—What’sLauragoingtodowhensheleavesschool?—Untilafewmonthsago,shewasthinkingofgoingtouniversity,butshe’sc
A、HavesomecoffeewithRob.B、Attendahistorylectureoncampus.C、DoherAlgebrahomeworkinthelibrary.D、Gotothebooksho
Thefoodweeatisinfluencedbysomanythings:ourgeography,ourhistory,ourclimateandourlifestyles.Sojustasacountry
—Doyouwantsomethingtoeat?Thefilmdoesn’tstartforanothertenminutesandI’mprettyhungry.—Sure,I’11havesomep
RareamongAmericanactors,DepphasmadeanameforhimselfeffortlesslyswitchingbetweenmainstreamHollywoodMoviesandmore
Theconversationended______whenshegotangryandputthephonedown.
Whendoesthisconversationprobablytakeplace?
【T1】我希望这个新学年成为对我的学生们有益的一年。(want…tobe)他们会在新学年学习很多东西,包括微积分、莎士比亚和失败。没错,就是失败。根据多种流传的说法,梭罗是个失败者。这位哈佛毕业生似乎把自己的大部分时间都用来在瓦尔登湖畔家
ThepoliceservicefortheUnitedKingdomisorganizedandcontrolledona(n)______basis.
Ionlyknowthemanby______butIhaveneverspokentohim.
随机试题
激励三要素是()
下列选项中,不属于社会结构的是()
项目经济费用效益分析中确定土地费用的原则是()。
《工伤保险条例》的规定,职工因工作遭受事故伤害或者患职业病需要暂停工作接受工伤医疗的,停工留薪期一般不超过()。
下列因素中,能够决定产业进入障碍大小的因素包括()。
境内居民企业A公司拥有B公司股份比例达到70%。而B公司又拥有C公司60%,C公司又拥有D公司55%,D公司又拥有E公司(外国公司)52%,在判断受控外国企业时。我们可以推定A公司持有E公司的股份是()。
培训前效果评估的内容包括()。
导生制的创行者是()
软件测试包括多个测试阶段,按照先后顺序排列正确的是
Heissuch______selfishmanthathehasn’t______leastconcernforothers.
最新回复
(
0
)