Migration of Birds
Orientation and Navigation
A .Factors in a bird's environment select for theexpression of migratory behavior, leading to the evolution of a migratorypattern or, on the other hand, to the loss of migratory abilities. Factors inthe environment function to provide direct, proximal stimulation for thephysiological preparation for migration. Factors in the environment alsoprovide information that allows birds to navigate during migratory passage.Navigation requires knowing three things: current location, destination, andthe direction to travel to get from the current location to the destination.Humans eventually learned to use both the sun and the stars to obtain thisinformation. Recently we invented more precise satellite-based technologiesthat have made these celestial cues for determining geographic positionssuperfluous and developed electronic aids to navigation that allow orientationwithout reference to the natural environment. Birds have successfully navigatedfor eons using environmental information.B .Birds are not alone in their ability to navigate longdistances. Fish, mammals, and even insects make migratory journeys. But theclarion honking of geese moving in huge skeins across the vault of the heavens,the twittering of migrants filtering down out of the night sky, the flocks ofnewly arrived birds filling woodlands, fields, and mudflats makes us most awareof the seasonal movements of birds and fills us with awe and wonder as to howsuch a magnificent event can be accomplished season after season, year afteryear, with such unerring precision.C .Of the three kinds of information necessary for navigation,we know something about the environmental cues that birds use to orient theirmigratory flight in the proper direction. On the other hand, there also iswell-supported experimental evidence that birds use neither the positions of thesun or the stars to know where they are or where they are to go. It has beenshown, however, that birds must learn both the location of the winter area aswell as the location of the breeding area in order to navigate properly, but wehave no idea what information they are learning. Nor do we know what cues birdsuse to know the location of their migratory destination when they are in theirwintering locale, often thousands of miles away. The capture of banded birds atthe same places along the route of the migratory journey in subsequent yearssuggests that some species also learn the location of traditional stop-oversites, but how they do that remains a mystery.D. European Starlings passthrough Holland on theirmigration from Sweden, Finland, and northwestern Russia to their winteringgrounds on the channel coast of France and the southern British Isles. Perdecktransported thousands of starlings from The Hague to Switzerland, releasingthese banded birds in a geographic location in which the population had neverhad any previous experience. The subsequent recapture of many of these bandedbirds demonstrated that the adults, which had previously made the migratoryflight, knew they had been displaced and returned to their normal winteringrange by flying a direction approximately ninety degrees to their usualsouthwesterly course. The juveniles, which had never made the trip before, incontrast, continued to fly southwest and were recaptured on the Iberianpeninsula. These first-year birds "knew "what direction to fly, butdid not recognize they had been displaced, thus ending up in an atypicalwintering range. In subsequent years these now adult birds returned to againwinter in Spain and Portugal. Coupled with another displacement of starlings tothe Barcelona coast in Spain, Perdeck concluded that the proper direction ofthe migratory flight was innate, that is, inherited in their DNA, since thenaive juveniles could fly that direction, and that the birds were alsogenetically programmed to fly a set distance. This is the same vector ordead-reckoning navigation program Lindberg used to fly from New York to Parisby maintaining a given compass direction (or directions) fora predeterminedtime (i.e., distance). But this study demonstrated that this navigation systemis modified by experience, since adults knew they were not in Holland anylonger and knew that in order to get to their normal wintering grounds theyneeded to fly a direction that they had never flown before! These results aretruly amazing. And we don't know how they did it.E. Displacement studies in the Western Hemisphereusing several species of buntings also demonstrated that birds recognized theyhad been moved and could fly appropriate, yet unique, routes to return to theirnormal range. Yet adult Hooded Crows transported latitudinally by over 600 kmfrom wintering grounds in the eastern Baltic to northwestern Germany failed to recognizethis displacement. In the spring they oriented properly but migrated to Sweden,west of their normal breeding range. This species used vector navigation, butdid not know the location of its traditional destination. Since it is generallyaccepted that migratory behavior evolved independently again and again indifferent bird populations, a single explanation to fit all cases perhapsshould not be expected.F .Most of the effort applied to understanding howbirds make a migratory flight has been directed toward environmental cues thatbirds use to maintain a particular flight direction. These cues are landmarkson the Earth's surface, the magnetic lines of flux that longitudinally encirclethe Earth, both the sun and the stars in the celestial sphere arching over theEarth, and perhaps prevailing wind direction and odors.Landmarks are useful as a primary navigationreference only if the bird has been there before. For cranes, swans, and geesethat migrate in family groups, young of the year could learn the geographic mapfor their migratory journey from their parents. But most birds do not migratein family flocks, and on their initial flight south to the wintering range orback north in the spring must use other cues. Yet birds are aware of thelandscape over which they are crossing and appear to use landmarks fororientation purposes. Radar images of migrating birds subject to a strong crosswindwere seen to drift off course, except for flocks migrating parallel to a majorriver. These birds used the river as a reference to shift their orientation andcorrect for drift in order to maintain the proper ground track. That majorgeographic features like Point Pelee jutting into Lake Erie or CapeMay at thetip of New Jersey are meccas for bird-watchers only reflects the fact thatmigrating birds recognize these peninsulas during their migration. Migratinghawks seeking updrafts along the north shore of Lake Superior or the ridges ofthe Appalachians must pay attention to the terrain below them in order to takeadvantage of the energetic savings afforded by these to pographic structures.G.Since humans learned to use celestial cues, it wasonly natural that studies were undertaken to demonstrate that birds could usethem as well. Soon after the end of the Second World War, Gustav Kramer showedthat migratory European Starlings oriented to the azimuth of the sun when heused mirrors to shift the sun's image by ninety degrees in the laboratory andobtained a corresponding shift in the birds' orientation. Furthermore, sincethe birds would maintain a constant direction even though the sun traversedfrom east to west during the day, the compensation for this movementdemonstrated that the birds were keeping time. They knew what orientation to thesun was appropriate at 9 a.m. They knew what different angle was appropriate atnoon, and again at 4 p.m. It has been recently shown that melatonin secretionsfrom the light-sensitive pineal gland on the top of the bird's brain areinvolved in this response. Not only starlings but homing pigeons, penguins,waterfowl, and many species of perching birds have been shown to use solarorientation. Even nocturnal migrants take directional information from the sun.European Robins and Savannah Sparrows that were prevented from seeing thesetting sun did not orient under the stars as well as birds that were allowedto see the sun set. Birds can detect polarized light from sunlight'spenetration through the atmosphere, and it has been hypothesized that thepattern of polarized light in the evening sky is the primary cue that providesa reference for their orientation.Using the artificial night sky provided by planetariumsdemonstrated that nocturnal migrants respond to star patterns.(quite analogousto Kramer's work on solar orientation, Franz Sauer demonstrated that if theplanetarium sky is shifted, the birds make a corresponding shift in theirorientation azimuth. Steve Emlen was able to show that the orientation was notdependent upon a single star, like Polaris, but to the general sky pattern. Ashe would turn off more and more stars so that they were no longer beingprojected in the planetarium, the bird's orientation became poorer and poorer.While the proper direction for orientation at a given time is probably innate,Emlen was able to show that knowing the location of "north" must belearned. When young birds were raised under a planetarium sky in whichBetelgeuse, a star in Orion of the southern sky, was projected to the celestialnorth pole, the birds oriented as if Betelgeuse was "north" when theywere later placed under the normally orientated night sky, even though inreality it was south!H. Radar studies have shown that birds do migrateabove cloud decks where landmarks are not visible, under overcast skies wherecelestial cues are not visible, and even within cloud layers where neither setof cues is available. The nomadic horsemen of the steppes of Asiaused theresponse of lodestones to the Earth's magnetic field to find their way, and thehypothesis that migrating birds might do the same was suggested as early as themiddle of the nineteenth century. Yet it was not until the mid-twentiethcentury that Merkel and Wiltschko demonstrated in a laboratory environmentdevoid of any other cues that European Robins would change their orientation inresponse to shifts in an artificial magnetic field that was as weak as theEarth's natural field. Although iron-containing magnetite crystals areassociated with the nervous system in homing pigeons, Northern Bobwhite, andseveral species of perching birds, it is unknown whether they are associatedwith the sensory receptor for the geomagnetic cue. An alternate hypothesis forthe sensory receptor suggests that response of visual pigments in the eye toelectromagnetic energy is the basis for geomagnetic orientation. It has beenshown, however, that previous exposure to celestial orientation cues enhancesthe ability of a bird to respond more appropriately when only geomagnetic cuesare available.Radar observations indicate that birds will decreasetheir air speed when their ground speed is augmented by a strong tail wind. Wealso know that birds can sense wind direction as gusts ruffling the feathersstimulate sensory receptors located in the skin around the base of the feather.Since there are characteristic patterns of wind circulation around high and lowpressure centers at the altitude most birds migrate, it has been hypothesizedthat birds could use these prevailing wind directions as an orientation cue. However,there presently is no experimental support for this hypothesis.I. The sense of smell in birds was considered for along time to be poorly developed, but more recent evidence suggests that somespecies can discriminate odors quite well. If the olfactory nerves of homingpigeons are cut, the birds do not return to their home loft as well as birdswhose olfactory nerves were left intact. A similar experiment has demonstratedthat European Starlings with severed olfactory nerves returned less often thanunaffected control birds even at distances as great as 240 km from their homeroosts. And even more interesting, when these starlings returned to the nestingarea the following spring, the starlings with nonfunctioning olfactory nervesreturned at a significantly lower frequency than the other starlings.J. Considering the array of demonstrated andsuggested cues that birds might use in their orientation, it is clear that theyrely upon a suite of cues rather than a single cue. For a migrating bird this redundancyis critical, since not all sources of orientation information are equallyavailable at a given time, nor are all sources of information equally useful ina given situation.
The passage on the previous pages has eight sections labeled A-J
Write the correct letter A-J in boxes1—8 on youranswer sheet.
1. The possible conclusion for migrating birds.
2. A description of olfactory nerves about birds’ distance.
3. A description of Latitude about several species.
4. Insights from studies how young birds find direction.
5. The ways birds can use for navigation.
6. Classes of animals for migratory movements.
7. The elements that birds have to navigation.
8. The birds use different cues to cope with weather.
Write your answers in boxes 9—11 on your answer sheet.
The list below gives some ways of regarding navigation.
Which THREE ways are mentioned by the writer of the text?
A. a exercise for young adult activity
B. Latitude for wintering ground
C. Physical surrounding
D. Weather cues
E. Satellite-based technologies
F. Places destination when they are in winter
Do the following statements agree with the information given in the passage?
In boxes 12—14 on your answer sheet, write
TRUE if the statement agrees with the information
FALSE if the statement contradictsthe information
NOT GIVEN if there is no information onthis
12. Birds’ migratory flight is affected by using natural environment.
13. Fish, mammals and insects are not in their ability to make migratory journeys.
14. Birds use cues to find their destination thousands of miles away.
“The time is up. please stop writing and waiting for submission”雅思考试是无声的战场。当上面这句话响起的时候，你是如释重负地放下了笔，期待着终有所获的成绩，还是犹豫又不甘心地停笔，懊恼地想这一场又无法和雅思分手呢?