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
2016-01-14
27
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. Salmons, 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【R1】______where they were born. What guide these fish upstream? According to scientists at the University of Wisconsin, salmon【R2】______and follow the fragrance of their native stream as they have a sharp【R3】______
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【R4】______from predators. Birds also migrate in order to find food and rear their young. It is discovered that birds are aided by【R5】______to make distant journeys that even human beings cannot make without the assistance of navigational instruments.
【R1】
选项
答案
the freshwater streams
解析
(文中举了鲑鱼例子来说明鱼类的迁移,文中第一段提到Salmon,for example,are bornin freshwater streams and soon afterward journey down to sea.“鲑鱼出生在淡水中,成长在海水中,”因而这里可以填写the freshwater streams。)
转载请注明原文地址:https://kaotiyun.com/show/yqAK777K
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
Theideaofhelpingpeoplecomesnaturallytomostofus.Ifweseeablindpersongettingoffabus,wewatchtomakesurethat
WhatdidsatelliteobservationsshowaboutdeforestationintheAmazon?
我劝他放弃计划,可他不听。(invain倒装句)
Theabilityto"see"oneselfinthefutureisaremarkablehumantrait—somewouldsayunique—thatisnotwellunderstood.That’
FormanyyearsafterheformedhisTheoryofRelativity,AlbertEinsteinvisitedmanyuniversitiesindifferentcitieswherehe
Whichnumbercomesnextinthisseriesofnumbers?23571113?
Manyforestsandgrasslandsacrosstheworldhavebeenshrinking—orevendisappearing—formanyyears.Theideaofrestoringfore
Ifitweretwohourslater,itwouldbehalfaslonguntilmidnightasitwouldbeifitwereanhourlater.Whattimeisitnow
对于一个公司来说,能跟上市场的发展变化是很重要的。(keeppacewith)
Capitalismcannotcureitselfofitsdestructiveinternalcontradiction.
随机试题
《酱油卫生标准》中规定的理化指标中,总砷的指标为()。
由影响线方程或机动法可知,静定结构的反力、内力影响线一定由直线或折线构成。()
关于胃液分泌的叙述,下列哪项是错误的?
远期外汇交易是为了满足客户保值或自身风险管理的需要,下列关于银行远期外汇交易的说法,不正确的是()。
氢离子浓度高的罐头食品的杀菌温度要求()氢离子浓度低的罐头食品。
阅读材料,回答相关问题。教科书的编写是为了更好地落实课程标准中的三维目标,教科书选取了多样化的教学内容。课程目标、内容选取与内容组织之间有密切的内在联系。教科书提供的是单纯的课程知识,在传统的课堂教学中,教师往往倾向于“封闭式
十八届六中全会提出,必须把()作为开展党内政治生活的首要任务。
近年来的高考作文命题,在朝材料作文方向转变,旨在鼓励学生独立思考,自由表达,这是一个积极的改革方向,可是,材料作文却遭遇学生缺乏思考能力的______________。去年高考作文,不独全国卷I的作文,其他一些省市的作文也被______________。
从所给的四个选项中,选择最合适的一个填入问号处,使之呈现一定的规律性:
一商店把某商品按标价的九折出售,仍可获利20%,若该商品的进价为每件21元,则该商品每件的标价为().
最新回复
(
0
)