Holly老師的英語新天地

Birdsong

The different ways birds acquire their songs have proved to be rich subjects for scientific investigation. The songs that have proved most useful in these studies are those that exhibit intermediate complexity. For example, the European chaffinch produces a 2-to 2.5-second burst of sound consisting of several sequences of repeated notes of different types. Individual chaffinches sing several variants of the song－all clearly recognizable as belonging to that species but differing in detail. Neighboring male chaffinches often have several songs in common, but each bird usually has its own individual mix of songs.

Such variability of birdsong raises intriguing questions about its origins. It has been known for some time that chickens and pigeons produce all their characteristic calls when isolated. Scientists wondered if the songs of chaffinches were similarly resistant to environmental influences. ■They also wonderer if the variants were genetically based. To answer these questions, researchers took young birds from the nest immediately after hatching and reared them alone in soundproof chambers. ■The following spring, when the males began singing in isolation, their song was recognizable as belonging to the chaffinch species but was much simpler in form and showed little variation either within or between individuals. ■Thus his experiment seems to indicate that the different song variants are due to some outside influence. ■A likely explanation is that this external source is the song of adult birds heard by young birds raised in their natural environment both in the nest and during their first spring, and this proved to be the case.

Work by researchers with an American finch, the white-crowned sparrow, presents a somewhat different and more complex picture of song learning. This bird has a wide range on the Pacific coast, and like the chaffinch, its songs vary. But they vary in a more systematic way in that birds from a given geographic area tend to sing similar song variants, as a result there are clear local dialects. If young males are taken immediately after hatching and isolated, as were the chaffinches, then no matter which region they come from, they all eventually sing very similar and simplified versions of the normal song. Obviously, in ordinary circumstances young males must pick up the local dialect by listening to adult birds and modifying their own simple song pattern accordingly. The researchers found that this learning process usually takes place during the first three months of life and thus before the bird has ever sung. Males captured when they are three months old and then reared alone begin to sing for the first time several months later, at which time they produce a recognizable version of the local dialect they were originally exposed to.

There are clear indications of a sensitive period for learning dialect characteristics. Up to three months of age, isolated males can be trained to sing their own or other dialects by playing tape-recorded songs for them, though the results of such experience do not show until the birds begin to sing themselves some months later. The young birds carry the memory of the songs they hear, and they reproduce them when they first sing. Beyond four months of age, the birds are unreceptive to any further training by tapes, and their songs, when they begin singing, are not affected. Thus for white-crowned sparrows there appears to be a simple, inherited song pattern that is sensitive to modification by learning but only during early life.

Other experiments have clarified the inherited element of the simple species song. It was found that when a fledgling is not only isolated from other birds but also prevented from hearing even the sound of its own voice, it produces only a series of disconnected notes that is quite unlike the recognizably white-crowned sparrow song produced by an isolated fledgling that is able to hear itself singing. Thus what is inherited is only the template or pattern for the simple song. The bird must still learn how to produce a song of that pattern. By comparing what its singing until it achieves a good fit with the inherited pattern.

Bird song鳥鳴

鳥類用不同方式學會唱歌，對科學調察而言題材豐富。這些研究中最有用的是表現exhibit（辭彙題）出證明這些歌曲中間的複雜性。然後舉了歐洲的chaffinch能鳴唱複雜的曲調。這些多變的曲調怎麼產生？科學家想知道，鳥類學會鳴唱和先天的基因有沒有關係，為了解開謎底，研究人員把剛孵出的幼鳥隔離致完全隔音的房間裡作一系列的實驗。

首先chaffinch的鳥鳴內容很豐富，在出生三個月內會從parents那裡學會鳴叫。並且在鳥鳴聲大致類似的基礎上，各個成鳥都有自己獨特的旋律。於是科學家想看看到底chaffinch這個本領是因基因遺傳還是後天學習。他們把一種美國東岸chaffinch的幼鳥從鳥群格哩，讓他聽不到其他鳥唱歌，結果發現他還是會唱歌，並且recongnizable是基本的屬於chaffinch特徵的鳴叫，但沒有正常的成鳥的豐富旋律，不像野生鳥唱的歌那麼複雜。於是科學家得出：因此認定chaffinch天生就有唱歌的能力，但是後天跟adult鳥的學習可以讓內容更豐富。然後相同情況下又做了個實驗，給他聽種鳥唱歌的磁帶，發現他們在投幾個月並不唱歌，而是hearing，這幾個月聽完之後才開始模仿磁帶的歌聲（有題），結果他的調調就和那些鳥一樣了。

研究者發現chaffinch的歌有口音，也就是後天學習的部份。不同地方的歌除了主音節（先天的）之外，同一個地區的chaffinch會唱類似的歌。有個實驗將剛孵化的幼鳥從一個地區帶到另一個地區，聽他們的叫聲表現，發現還是跟原本地區的叫聲有類似，由此可以證明鳥的鳴叫聲也跟遺傳有關係。然後進一步探討了後天學習的時間期限，做了另一個實驗，如果在white-crowned Sparrow，出生後的三個月內，把做過實驗只會發出單音而不會唱歌的white-crowned Sparrow放回去野外，發現他們又開始學唱歌了，不過倘若躺過三個月，即便他們返回鳥群也不在對成鳥的叫聲有反應了（not responsive to），他們發出聲音很單調，類似上一個實驗的結果，因為他們有學習的期限，即生出後的三個月。

另外科學家還做另一個實驗：如果鳥聽不到自己的歌聲會怎樣。如果不讓被分離的幼鳥聽到自己的聲音，那他們只能發一寫簡單的不連續的unrecongnizable的聲音，稱不上是歌聲，這說明了在不聽別的聲音的情況下，小鳥不能自己教自己唱歌（同義改寫題）。科學家發現white-crowned Sparrow還有dialect。不同的地方的同種小鳥唱歌是有一些區別的。如果把野生white-crowned Sparrow在出生三個月內，換到另外一種口音的群體中，則他會學習新群體的口音，而不是native的歌，說明他們的dialect也受後天地域影響的（有題）；不過若是出聲超過三個月，則他們的口音就不會改了。

相對於上一段的實驗，文末提到chaffinch則是沒有學習期限，不管出生多久，只要把它們放到新群體中，他就會學到新群體的口音。

最後考了一題分類題：

chaffinch的特徵：鳴叫聲受遺傳影響（離群長大後也能發出大致的鳴叫）。

white-crowned Sparrow的特徵：鳴叫聲主要是靠後天學習（有三個月學習期限）；如果幼鳥自己聽不到自己的聲音的話，基本不會鳴叫。

兩種鳥都有的特徵：幼鳥離群長大後發出簡單的鳴叫（共同特點僅此一個）。

辭彙題：

Exhibit，選show

Intriguing，選interesting

unacceptable      

Q1. The word “exhibit” in the passage is closest meaning to

A1. show

Q2. According to paragraph 1, all of the following statements about the songs of chaffinches are true Except

A2. The songs consist of a single note repeated several times.

Q3. The word “intriguing” in the passage is closest in meaning to

A3. interesting

Q4. According to paragraph 2, why did researchers take young chaffinches from their nests?

A4. To investigate the contribution of inheritance to birdsong

Q5. According to paragraph 2, what did researchers discover was the most significant influence on variability in the song development of young chaffinches?

A5. The opportunity for young chaffinches to develop their own song styles in isolation

Q6. The word “modifying” in the passage is closest in meaning to

A6. adjusting

Q7. The final sentence of paragraph 3 serves which of the following purposes in the paragraph’s exposition?

A7. It details and supports the earlier claim that dialect learning takes place before song production.

Q8. Paragraph 4 supports which of the following conclusions about a male white-crowned sparrow that is isolated for the first four months of its and then returned to the locale of its birth?

A8. It would sing the sample species song but not the local dialect of its native area.

Q9. The phrase “unreceptive to” in the passage is closest in meaning to

A9. unresponsive to

Q10. 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.

A10. An isolated white-crowned sparrow fledgling will produce the species song unless it cannot hear itself sing, in which case it produces only disconnected notes.

Q11. Paragraph 5 answers which of the following questions about the song of white-crowned sparrows?

A11. Can a young white-crowned sparrow teach itself a song it cannot hear?

Q12. Look at the four squares [■] that indicate where the following sentence could be added to the passage.

If variant songs resulted from individual creativity or genetic variation, then the researchers would have observed variants among the isolated chaffinches.

A12. (C)

Q13.Directions: From the six statements below, select the one statement that is true ONLY of chaffinches, the statements that are ONLY of white-crowned sparrow, and the two statements that are true of BOTH chaffinches and white-crowned sparrows. Drag each phrase you select into appropriate column of the table. One statement will NOT be used. This question is worth 3 points.

A13.

Chaffinches but NOT white-crowned sparrows

●   Birds raised in isolation sing simple versions of their species’ characteristic song.

White-crowned sparrows but NOT chaffinches

●   Adults from different regions of the species’ range sing different dialects.

●   Song variants must be learned months before they are first sung.

    BOTH chaffinches AND white-crowned sparrows

●   In their natural environment, young birds learn song variants from adults of their species.