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
71
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.
【R5】
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 usecelestial clues.因而摘要中可以归纳为celestial clues。)
转载请注明原文地址:https://www.kaotiyun.com/show/VqAK777K
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
DuringWorldWarIIattheheightoftheblitzonEastLondon,aboyof12wasfoundwanderingtherubblestreetsnearTowerBri
Althoughfewwoulddenythatit’sbettertoberichthanpoor,forsomepeoplethequestformoneyissoall-consumingthatite
Althoughfewwoulddenythatit’sbettertoberichthanpoor,forsomepeoplethequestformoneyissoall-consumingthatite
TodaythecaristhemostpopularsortoftransportationinalloftheUnitedStates.Ithascompletelyre【77】thehorseasam【7
AdvancenoticeisoftenreferredtoinAmericaas"leadtime,"anexpressionwhichissignificantinaculturewhereschedulesa
BecauseJenkinsneither______nordefendseithermanagementorthestrikingworkers,bothsidesadmirehisjournalistic
人们因政府在毒品交易问题上所表现出的漠不关心的态度而感到担心。
Mercury,theplanetnearestthesun,isdifficulttoobservefromtheEarthbecauseitrisesandsetswithintwohoursofthesu
并不是任何人都允许进入某些政府办公大楼的。(allow)
Thegamewascancelledbecausemostoftheteammembers______amatchwithoutastandardcourt.
随机试题
支气管肺段
患者男性,65岁。吸烟史近40年,患慢性支气管炎近20年,经常咳嗽、咳痰;近几年时常觉胸闷、呼吸困难。入院查体:桶状胸,胸廓呼吸运动减弱;叩诊呈过清音,心浊音界缩小,肝浊音界下降;听诊呼吸音减弱,呼气延长。该患者可能患
分子伴侣不具有的功能是
男性,30岁,炼钢工人,工作中不慎被烧伤,三度烧伤面积达60%,应采用
芽孢属于细菌的()。
保险公司技术上无偿付能力是指()。
文明的进展并不完全像是一股奔腾直前、日趋佳境的巨流。如果我们用一种相当大的比例尺把它绘制成图,也许会具有上述外观。但这种广泛的看法往往会____________细节,而我们对这一过程的全部理解却必须____________于这种细节。假如我们从绵延几万年的
甲于1998年1月犯盗窃罪(盗窃金额5000元),在公安机关立案侦查后逃亡外地,又于2004年4月犯抢劫罪。关于甲的行为说法正确的是()
OneofNature’smostexcitingmysteriesishowpigeonsfindtheirwayhomeovervastdistances.NowGermanscientistsbelieveth
TheSky’sLimitAirtravelisarapidlygrowingsourceofgreenhousegases.Butitisalsoanindispensablewayoftravel.T
最新回复
(
0
)