首页
登录
职称英语
The annals of natural history contain many astonishing examples of the abili
The annals of natural history contain many astonishing examples of the abili
游客
2024-08-11
22
管理
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.
Question 71 to 75
Complete the summary below with information from the passage, using three words fo fewer for each blank.
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. [br] 【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 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://tihaiku.com/zcyy/3714804.html
相关试题推荐
ThestudentislookingfortheEconomichistoryoffice.[br][originaltext]M:H
ThestudentislookingfortheEconomichistoryoffice.[br][originaltext]M:H
ThestudentislookingfortheEconomichistoryoffice.[originaltext]M:Hello.
Renaissancewastherevivalofclassical______inEuropeanhistory.A、educationan
Itisnaturalforyoungpeopletobecriticaloftheirparentsattimesand
Itisnaturalforyoungpeopletobecriticaloftheirparentsattimesand
Itisnaturalforyoungpeopletobecriticaloftheirparentsattimesand
Itisnaturalforyoungpeopletobecriticaloftheirparentsattimesand
Itisnaturalforyoungpeopletobecriticaloftheirparentsattimesand
Itisnaturalforyoungpeopletobecriticaloftheirparentsattimesand
随机试题
WhichofthefollowingisTRUEaboutthegeneralmanagerandhisassistants?[br
Almosteveryonewithorwithoutacomputerisawareofthelatesttechnologi
AccordingtoUNICEF,around564millionIndians,nearlyhalfthepopulation,
对于艾滋病,哪项是不恰当的A.可通过胎盘感染胎儿、软产道、母乳感染新生儿 B.
《证券投资顾问业务风险揭示书》至少应包含的内容() Ⅰ.提示投资者在接受
某服装店销售一款新款服装,分三阶段销售。第一阶段按原价出售,共售出总数的40%;
(2015年真题)期货公司应当提示客户可以通过(),查询期货交易结算结果和
2021年2月王某在某房产公司举办的有奖购房活动中中奖获得一辆小汽车,房产公司提
下列造成质量数据波动的原因中,属于偶然性原因的是( )。A.现场温湿度的微小变
某地下工程合同约定:计划1月份开挖土方80000m3,2月份开挖160000m3
最新回复
(
0
)