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
2023-10-16
28
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.
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. [br] 【R4】
选项
答案
find protection
解析
(文章第二段提到Like many other seabirds,they find protection from cats,foxes,and otherpredators on isolated islands.即他们喂养自己的后代并想办法保护自己的食物,这是鸟类迁移的原因之一。)
转载请注明原文地址:https://tihaiku.com/zcyy/3101811.html
相关试题推荐
Theideaofhelpingpeoplecomesnaturallytomostofus.Ifweseeablind
Theideaofhelpingpeoplecomesnaturallytomostofus.Ifweseeablind
Theideaofhelpingpeoplecomesnaturallytomostofus.Ifweseeablind
Theideaofhelpingpeoplecomesnaturallytomostofus.Ifweseeablind
Theideaofhelpingpeoplecomesnaturallytomostofus.Ifweseeablind
Howmanycirclescontainablackdot?[img]2012q2/ct_eyyjscm_eyyjsciq_0097_20123
剑桥大学是具有700多年历史的世界著名学府。(withahistoryof)CambridgeUniversityisaworld—renowne
Sometincanshavelosttheirlabels.3containsoup,4containbeans,and1con
Thepresident’seducationspeechescontained______thetongueleadingtopublicc
Whichtwowordsstartingwith"P"and"0"containthemostletters?PostOffice.(
随机试题
Whichofthefollowingpairscontainsphonemiccontrast?A、peat,peelB、pea,pee
You’dthinkPaulineHordwouldhaveservedhertimebynow.Afterall,sher
[originaltext]M:Shawn’sbeentryingformonthstofindajob.ButIwonderhow
关于产权持有人,以下说法错误的是()。A.产权持有人,是指评估对象的产权持
只接受公正、公平、合理的职业报酬,是A.执业药师的执业行为规范 B.执业药师的
与药物从肾排泄的快慢无关的是A.肾小管分泌功能 B.生物利用度 C.肾小球滤
下列估价师的行为中,不符合估价规范的有( )。A.仅要求委托人提供估价对象权属
()都是为了使顾客手中的产品随时可用。 A.可用性B.维修保障C.可信性
在设备招标的综合评估法评标中,以下说法正确的是( )。 A.每个评标委员会成
国家根据病原微生物的传染性、感染后对个体或者群体的危害程度,将病原微生物分A.三
最新回复
(
0
)