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
59
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
remembers
解析
(文章第一段提到The most reasonable theory to explain salmon homing is that each individual remembers the distinctive "fragrance" of its native stream. “对鲑鱼这种迁移最合理的解释就是它们都能记住它们出生地的水流的味道。”)
转载请注明原文地址:https://kaotiyun.com/show/dWAK777K
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
Yesterdayyoulostyourstudentidentificationcard.WritetotheDirectorofStudentServicesexplainingthesituation,stating
ImaginetakingashipacrossthePacificOcean.Onedayyoulookoutatthewaterandseealayerofgarbagethatextendsallthe
WhichisNOTcorrectaboutSouthSudanaccordingtothenewsitem?
Bythemid-19thcenturymostofEuropewasinthefirststageofthedemographictransition.Deathratehaddecreased,aswars,f
RareamongAmericanactors,DepphasmadeanameforhimselfeffortlesslyswitchingbetweenmainstreamHollywoodMoviesandmore
TheAmericanbabyboomafterthewarmadeunconvincingU.S.advicetopoorcountriesthattheyrestraintheirbirths.However,t
ScientistssaytherehasbeenaseveredecreaseintheamountofwaterinLakeChadinnorthernAfricainthelastthirtyyears.
Wheredoesthisconversationprobablytakeplace?
Whatisthewordcoiledinsidethiscircle?NGOERRTS
PrinceCharles,thelongest-waiting_________tothethroneinBritishhistory,hasspokenofhis"impatience"togetthingsdone
随机试题
A.椎一基底动脉血栓形成B.大脑前动脉血栓形成C.大脑中动脉血栓形成D.蛛网膜下腔出血E.小脑出血有偏瘫、同向性偏盲、偏身感觉障碍,见于
继发孔型房间隔缺损的分类中不包括
某施工单位承担了矿山井巷工程,与业主签订了建设施工合同,合同约定工期15个月,开工日期为2005年11月1日,竣工日期为2007年1月31日。工期奖惩额为5000元/d,工程保修期1年。在施工过程中,由于发生地质条件变化,建设单位进行设计变更,影
()是被保险人实现其保险权益的具体体现
A公司是一个注册经营地在美国的一家企业,A公司有一个100%子公司经营注册在德国,现有一个中国公司B要到美国去收购A公司。现需要对A公司的股权和B公司的股权市场价值进行评估,评估师在评估B公司股权市场价值时应该选择()。
下列各项中,属于可转换债券筹资特点的有()。
阅读下面的材料,根据要求写作。东邻人家的岳母死了,殡葬的时候需要一篇祭文,这家人就托私塾的老师帮忙写一篇。塾师便从古本里规规矩矩地抄了一篇,没想到误抄了悼念岳丈的祭文。葬礼正在进行的时候,识字的人发现这篇祭文完全弄错了。这一家人跑回私塾去责问塾师
攻击性行为产生的直接原因主要是()。
Howlongcanthemankeephisbooks?
Iremember______(see)herlastyearatMary’sbirthdayparty.
最新回复
(
0
)