原文：
A
For manyof US, the way birds are able to orientate is both astounding and difficult toappreciate fully. For instance, the annual migration of tire golden plover ofthe Pacific takes it from Alaska to Hawaii on a flight of well over 3000kilometres, and if it were to deviate by only one degree, it would miss theisland on which it nests.
B
The first systematic studies on orientation in birds were made possible by the‘homing instinct’ exhibited by so many species. Birds are caught at a time whenthey show an attachment to their territory, especially during the nestingseason. They are taken to some spot, released, and the percentage of returns isrecorded. The distance can be varied, and the direction, as well as the methodof transporting them, and then the influence of climatic and other factors ontheir ability to find their way home can be studied. These experiments haveshown a wide variation in ability to home, and three types of homing behaviourhave been identified.
C
In the first type, birds methodically explore the area in which they are releaseduntil they pick up some familiar feature, and then they quickly find their wayback to the nest. Such birds possess a highly developed visual memory, asexperiments with pigeons have shown. Domestic pigeons have been trained to peckat a certain point on an aerial photograph, with a system of rewards, and fouryears later the birds were still able to respond to this training when placedon the aerial photograph. Birds’ eyes have a power of resolution two to threetimes greater than ours, enabling them to pick up very fine details. If a birduses only this type of homing behaviour, however, it can only succeed if thepoint of release is not too far away. If the birds are transported 800kilometres from their nest, it is only by good fortune that they find their wayback as a result of long exploratory flights. Usually, the area known to a birdis its feeding territory. Released within this area, the birds soon make theirreturn; release them outside it and far fewer return. However, if a bird isreleased for a second time in the same place, its visual memory comes intoplay, and the bird, no longer requiring tedious exploratory flights, willreturn much more quickly.
D
The second type of homing behaviour is shown by birds that are capable of choosingtheir flight direction and holding to it for the rest of their journey. How dothey decide what direction to take? They appear to choose their normalmigration direction even if they are released in a different place from theirusual stalling point. If, for example, birds which normally fly to thenorth-east to reach latitude 45 degrees north are released at that latitude,they will immediately start flying north-east anyway. So if they’re releasedfurther to the west, they’ll maintain the correct direction, but fly west oftheir destination, and so fail to arrive.
E
The third type of homing behaviour shows the highest degree of orientation.Released at one point, the birds immediately take stock of it, compare itsposition with that of the nest, decide on the direction and fly off. Thishappens even if the birds are in a country right off their migration routes,where they have never been before. In one example, a laysan albatross returnedto its nesting area on Midway Island in the middle of the Pacific, having flownover 5000 kilometres from the west coastal of the USA in just over ten days.This is a perfect example of the third type of homing, for the albatrossclearly couldn’t rely on any landmarks over the vast expanse of the PacificOcean.
F
The percentage of successful birds varies greatly, being highest in those specieswith a strong migratory behaviour. Thus the lesser black-backed gull is moremigratory than the herring gull and more often reaches ‘home’.
Great migrants such as the swift have thehighest percentage of returns. In one case, seven out of nine alpine swiftswere recaptured at their nests after being displaced some 1400 kilometres; onemade the journey in three days.
G
What partdoes heredity play in all this? Two research studies suggest that instinctive,i.e. genetically inherited, behaviour patterns play a part in navigation. Thefirst was carried out by Ernst Schuz and it is highly significant. Schuz caughtfirst year European storks and released them later, after the departure of theadult storks at a time when they normally make their south-west autumnmigration to Africa. The recaptures showed that, in spite of thefact that therewere no adults to guide them, the birds unanimously headed south-west. This wasa most striking finding, for it showed that the birds had an innate andunlearned attraction for the African wintering area that they have occupied forthousands of years.
H
The case of starlings is a little different. These birds have a great aptitude forhoming, but this behaviour differs in the different age groups. Birds that wereshifted to the south-east of their normal migration route split into two lots.The adults, in full possession of their gift for orientation, found theirwintering area by modifying their direction by 90 degrees, whereas thejuveniles sought their winter quarters to the south-east of their realposition.
Questions 14-18
Complete the summery below.
Choose NO MORE THAN TWO WORDS from thepassage for each answer. Write your answers in boxes 14-18 on your answersheet.
Types of homing behaviour
First type:
Birds rely on their sophisticated14.................... However, they are generally most successful if they arereleased within their feeding territory.
Second type:
Birds select their accustomed15.................. , no matter where they are released. As a result, they maymiss their 16.....................
Third type:
Birds orientate correctly, even when theyare released in an unfamiliar place and have no 17........................ tomake use of. One bird with this type of skill is the 18.....................
Questions 19-22
Reading Passage has eight paragraphs, A-H
Which paragraph contains the followinginformation?
Write the correct letter, A-H, in boxes19-22 on your answer sheet.
NB You may use any letter more than once.
19 the effects of distance on some birds’ability to find their nests
20 a methodology for testing the generalability of birds to find their nests
21 one aspect of physical ability in humansand birds
22 how some birds’ migration was delayed forexperimental purposes
Questions 23-26
Look at the following types of birds(Questions 23-26) and the list of points which the author wishes to illustratebelow.
Match each bird with the point which itillustrates, A-G.
Write the correct letter, A-G, in boxes23-26 on your answer sheet.
23 ........................domestic pigeon
24 ........................alpine swift
25 ........................European stork
26 ........................starling
List of points which the author wishes toillustrate
A an ability to orientate without previoustraining
B the speed at which birds can fly
C the ability to remember things seenpreviously
D the effect of age on homing ability
E the strength required to fly a greatdistance
F a high success rate in finding nests
G the importance of seasonal cues formigrating birds
Answer keys
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