Birdsong is the classic example of how genes (hereditary information) and environment both have a crucial role to play in the behavioral development of animals. Since the pioneering work of W. H. Thorpe on chaffinches (a common European bird), many species have been studied, and it has become clear both that learning plays an important role for all species and also that there are constraints on what they are able to learn.
Thorpe was able to show that learning from others was involved in chaffinch birds through a series of experiments on hand-reared chicks (young birds). As in most other species, only the males sing. Thorpe found that, if he raised young males in total isolation from all others, the song they produced was quite different from that of a normal adult. It was about the right length and in the correct frequency range. It was also split up into a series of notes as it should be. But these notes lacked the detailed structure found in wild birds, nor was the song split up into distinct phrases as it usually is. This suggested that song development requires some social influence. Later experiments in which researchers played recordings of songs to young birds showed just how precise this influence was: many of them would learn the exact pattern of the recording they had heard. A remarkable feature here was that birds were able to copy precisely songs that they only heard in the first few weeks of life, yet they did not sing themselves until about eight months old. They are thus able to store a memory of the sound within their brain and then match their own output to their recollection of it when they mature.
Young chaffinches normally learn only chaffinch song, though Thorpe found they could be trained to sing the song of a tree pipit (another type of bird), which is very similar to that of their own species. ■In general, however, the constraints on learning which birds have ensure that they only learn songs appropriate to the species to which they themselves belong. ■These constraints may be in their brain’s circuitry, the young bird hatching with a rough idea of the sounds that it should copy. ■The crude song of a bird reared in isolation gives some clues as to what this rough idea may be: the length, the frequency range and the breaking up into notes are all aspects of chaffinch song shared between normal birds and those reared in isolation. ■In other cases the constraints are more social, young birds only being prepared to learn from individuals with whom they have social interactions. Thus, in a number of species, it has been found that they will not copy from recordings, but will do so from a live tutor. In some cases this may occur when they are young birds, but in others the main learning period is when they set up their territories and interact with neighbors for the first time, enabling them to match their neighbor’s songs and so counter-sing with them. Whatever the nature of the learning rules in a particular species, there is no doubt that they are effective; it is very unusual to hear a wild bird singing a song which is not typical of its own species despite the many different songs which often occur in a small patch of woodland.
However, not all birds show the same learning pattern as do chaffinches. There are some species which produce normal sounds even if deaf, so that they cannot hear their own efforts, much less copy those of others. The cooing of doves and the crowing of cocks are examples here. In other cases, such as parrots and hill mynahs, birds can be trained to copy a huge variety of sounds, though those they learn in the wild are usually more restricted. The amazing capability of mynahs has apparently arisen simply because birds in an area learn a small number of their calls from each other, males from males and females from females, and these calls are highly varied in structure. The ability to master them has led the birds, incidentally, to be capable of saying “hello” and mimicking a wide variety of other sounds.
1. The word “pioneering” in the passage is closet in meaning to
2. The word “distinct” in the passage is closet in meaning to
3. According to paragraph 2, all of the following are characteristics of the songs of the young chaffinches in Thorpe’s experiment EXCEPT:
A. They were not identical to the songs of normal adult chaffinches.
B. They lacked the complex form of the songs of wild chaffinches.
C. They were as long as the songs of normal adult chaffinches.
D. They were clearly different from each other.
4. According to paragraph 2, researchers discovered which of the following by playing recordings of songs to chaffinches?
A. Chaffinches could no longer be taught to reproduce sounds after the first few weeks of life.
B. Chaffinches could not reproduce songs with exactly the same patterns of recorded songs.
C. Chaffinches at the age of eight months could recall and reproduce a song that they heard in the first few weeks of life.
D. Chaffinches that learned a song from recordings in the first few weeks of life were later unable to copy the sounds of mature chaffinches.
5. All of the following are mentioned in paragraph 2 as characteristics of wild chaffinches EXCEPT:
A. They are able to copy songs very precisely.
B. Their song development requires interaction with other chaffinches.
C. Their songs are not as well-structured as the songs of other birds.
D. It is the males of the species that do the singing.
6. The word “enabling” in the passage is closet in meaning to
7. It can be inferred from paragraph 3 that one of the functions of songs in birds is to
A. bring together birds living in groups with birds living in isolation
B. help young birds distinguish other young birds from adults
C. make possible interactions between birds of different species
D. help birds to establish territories
8. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. Songs produced by chaffinches reared in isolation are cruder than the songs of wild birds.
B. The song of a bird reared in isolation suggests which aspects of chaffinch song may be inborn.
C. Comparing the crude songs of chaffinches reared in isolation to the songs of wild chaffinches suggests differences as well as similarities.
D. Studying the song aspects of chaffinches reared in isolation, researchers have gained a better understanding of the songs produced by wild birds.
9. According to paragraph 3, in some species, young birds do not copy songs from recordings because
A. they learn to sing only by live interactions with other birds
B. their ability to learn from recordings occurs later in life
C. they can only learn the songs of the birds living in their area of woodland
D. they can only learn songs from other birds of their own species
10. Why does the author mention that it is very unusual to hear a wild bird singing a song which is not typical of its own species?
A. To explain why a variety of different bird songs are often heard in a relatively small area
B. To argue that social constraints have a greater impact upon learning than do genetic constraints
C. To provide an example of how the process of learning rules varies from one species to another
D. To illustrate how effective the different constraints upon learning are in young birds
11. The word “restricted” in the passage is closet in meaning to
12. According to paragraph 4, why are mynahs able to learn to make a wide variety of sounds?
A. They have the ability to imitate any sound that they are exposed to.
B. The frequency with which mynahs travel from one small area to another exposes them to a wide variety of sounds.
C. They are exposed in the wild to calls that are very different from each other.
D. An acute sense of hearing allows them to listen to and copy many different sounds.
13. Look at the four squares [■] that indicate where the following sentence can be added to the passage.
Are these constraints genetic, environmental, or both?
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.
Q1C Q2C Q3D Q4C Q5C Q6A Q7C Q8B Q9A Q10D
Q11C Q12C Q13 B