Many signals that animals make seem to impose on the signalers costs that are overly damaging. A classic example is noisy begging by nestling songbirds when a parent returns to the nest with food. These loud cheeps and peeps might give the location of the nest away to a listening hawk or raccoon, resulting in the death of the defenseless nestlings. In fact, when tapes of begging tree swallows were played at an artificial swallow nest containing an egg, the egg in that “noisy” nest was taken or destroyed by predators before the egg in a nearby quiet nest in 29 of 37 trials.
Further evidence for the costs of begging comes from a study of differences in the begging calls of warbler species that nest on the ground versus those that nest in the relative safety of trees. The young of ground-nesting warblers produce begging cheeps of higher frequencies than do their tree-nesting relatives. These higher-frequency sounds do not travel as far, and so may better conceal the individuals producing them, who are especially vulnerable to predators in their ground nests. David Haskell created artificial nests with clay eggs and placed them on the ground beside a tape recorder that played the begging calls of either tree-nesting or of ground-nesting warblers. The eggs “advertised” by the tree-nesters' begging calls were found bitten significantly more often than the eggs associated with the ground-nesters' calls.
The hypothesis that begging calls have evolved properties that reduce their potential for attracting predators yields a prediction: baby birds of species that experience high rates of nest predation should produce softer begging signals of higher frequency than nestlings of other species less often victimized by nest predators. This prediction was supported by data collected in one survey of 24 species from an Arizona forest, more evidence that predator pressure favors the evolution of begging calls that are hard to detect and pinpoint.
Given that predators can make it costly to beg for food, what benefit do begging nestlings derive from their communications? One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health, making it worthwhile for the listening parent to give it food in a nest where several other offspring are usually available to be fed. If this hypothesis is true, then it follows that nestlings should adjust the intensity of their signals in relation to the signals produced by their nestmates, who are competing for parental attention. When experimentally deprived baby robins are placed in a nest with normally fed siblings, the hungry nestlings beg more loudly than usual—but so do their better-fed siblings, though not as loudly as the hungrier birds.
If parent birds use begging intensity to direct food to healthy offspring capable of vigorous begging, then parents should make food delivery decisions on the basis of their offsprings’ calls. Indeed, if you take baby tree swallows out of a nest for an hour feeding half the set and starving the other half, when the birds are replaced in the nest, the starved youngsters beg more loudly than the fed birds, and the parent birds feed the active beggars more than those who beg less vigorously.
As these experiments show, begging apparently provides a signal of need that parents use to make judgments about which offspring can benefit most from a feeding. But the question arises, why don't nestlings beg loudly when they aren't all that hungry? By doing so, they could possibly secure more food, which should result in more rapid growth or larger size, either of which is advantageous. The answer lies apparently not in the increased energy costs of exaggerated begging——but rather in the damage that any successful cheater would do to its siblings, which share genes with one another. An individual's success in propagating his or her genes can be affected by more than just his or her own personal reproductive success. Because close relatives have many of the same genes, animals that harm their close relatives may in effect be destroying some of their own genes. Therefore, a begging nestling that secures food at the expense of its siblings might actually leave behind fewer copies of its genes overall than it might otherwise.
Paragraph 1: Many signals that animals make seem to impose on the signalers costs that are overly damaging. A classic example is noisy begging by nestling songbirds when a parent returns to the nest with food. These loud cheeps and peeps might give the location of the nest away to a listening hawk or raccoon, resulting in the death of the defenseless nestlings. In fact, when tapes of begging tree swallows were played at an artificial swallow nest containing an egg, the egg in that “noisy” nest was taken or destroyed by predators before the egg in a nearby quiet nest in 29 of 37 trials.
1. The phrase “impose on” in the passage is closest in meaning to
○ increase for
○ remove from
○ place on
○ distribute to
2. According to paragraph 1, the experiment with tapes of begging tree swallows establishes which of the following?
○ Begging by nestling birds can attract the attention of predators to the nest.
○ Nest predators attack nests that contain nestlings more frequently than they attack nests that contain only eggs.
○ Tapes of begging nestlings attract predators to the nest less frequently than real begging calls do.
○ Nest predators have no other means of locating bird nests except the begging calls of nestling birds.
Paragraph 2: Further evidence for the costs of begging comes from a study of differences in the begging calls of warbler species that nest on the ground versus those that nest in the relative safety of trees. The young of ground-nesting warblers produce begging cheeps of higher frequencies than do their tree-nesting relatives. These higher-frequency sounds do not travel as far, and so may better conceal the individuals producing them, who are especially vulnerable to predators in their ground nests. David Haskell created artificial nests with clay eggs and placed them on the ground beside a tape recorder that played the begging calls of either tree-nesting or of ground-nesting warblers. The eggs “advertised” by the tree-nesters' begging calls were found bitten significantly more often than the eggs associated with the ground-nesters' calls.
3. The word “artificial” in the passage is closest in meaning to
○ attractive
○ not real
○ short-term
○ well designed
4. Paragraph 2 indicates that the begging calls of tree nesting warblers
○ put them at more risk than ground-nesting warblers experience
○ can be heard from a greater distance than those of ground-nesting warblers
○ are more likely to conceal the signaler than those of ground-nesting warblers
○ have higher frequencies than those of ground-nesting warblers
5. The experiment described in paragraph 2 supports which of the following conclusions?
○ Predators are unable to distinguish between the begging cheeps of ground-nesting and those of tree-nesting warblers except by the differing frequencies of the calls.
○ When they can find them, predators prefer the eggs of tree-nesting warblers to those of ground-nesting warblers.
○ The higher frequencies of the begging cheeps of ground-nesting warblers are an adaptation to the threat that ground-nesting birds face from predators.
○ The danger of begging depends more on the frequency of the begging cheep than on how loud it is.
Paragraph 3: The hypothesis that begging calls have evolved properties that reduce their potential for attracting predators yields a prediction: baby birds of species that experience high rates of nest predation should produce softer begging signals of higher frequency than nestlings of other species less often victimized by nest predators. This prediction was supported by data collected in one survey of 24 species from an Arizona forest, more evidence that predator pressure favors the evolution of begging calls that are hard to detect and pinpoint.
6. The word “prediction” in the passage is closest in meaning to
○ surprise
○ discovery
○ explanation
○ expectation
7. The word “pinpoint” in the passage is closest in meaning to
○ observe
○ locate exactly
○ copy accurately
○ recognize
Paragraph 4: Given that predators can make it costly to beg for food, what benefit do begging nestlings derive from their communications? One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health, making it worthwhile for the listening parent to give it food in a nest where several other offspring are usually available to be fed. If this hypothesis is true, then it follows that nestlings should adjust the intensity of their signals in relation to the signals produced by their nestmates, who are competing for parental attention. When experimentally deprived baby robins are placed in a nest with normally fed siblings, the hungry nestlings beg more loudly than usual—but so do their better-fed siblings, though not as loudly as the hungrier birds.
8. The word “derive” in the passage is closest in meaning to
○ require
○ gain
○ use
○ produce
Paragraph 4: Given that predators can make it costly to beg for food, what benefit do begging nestlings derive from their communications? One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health, making it worthwhile for the listening parent to give it food in a nest where several other offspring are usually available to be fed. If this hypothesis is true, then it follows that nestlings should adjust the intensity of their signals in relation to the signals produced by their nestmates, who are competing for parental attention. When experimentally deprived baby robins are placed in a nest with normally fed siblings, the hungry nestlings beg more loudly than usual—but so do their better-fed siblings, though not as loudly as the hungrier birds.
Paragraph 5: If parent birds use begging intensity to direct food to healthy offspring capable of vigorous begging, then parents should make food delivery decisions on the basis of their offsprings’ calls. Indeed, if you take baby tree swallows out of a nest for an hour feeding half the set and starving the other half, when the birds are replaced in the nest, the starved youngsters beg more loudly than the fed birds, and the parent birds feed the active beggars more than those who beg less vigorously.
9. In paragraphs 4 and 5, what evidence supports the claim that the intensity of nestling begging calls is a good indicator of which offspring in a nest would most benefit from a feeding?
○ When placed in a nest with hungry robins, well-fed robins did not beg for food.
○ Among robin nestlings, the intensity of begging decreased the more the nestlings were fed.
○ Hungry tree swallow nestlings begged louder than well-fed nestlings in the same nest.
○ Hungry tree swallow nestlings continued to beg loudly until they were fed whereas well-fed nestlings soon stopped begging.
10. It can be inferred from paragraphs 4 and 5 that parent songbirds normally do not feed
○ nestlings that are too weak to beg for food as vigorously as their nestmates
○ more than one hungry nestling during a single visit to the nest
○ offspring that were fed by the parents on the previous visit to the nest
○ nestlings that have been removed and then later put back into their nest
Paragraph 6: As these experiments show, begging apparently provides a signal of need that parents use to make judgments about which offspring can benefit most from a feeding. But the question arises, why don't nestlings beg loudly when they aren't all that hungry? By doing so, they could possibly secure more food, which should result in more rapid growth or larger size, either of which is advantageous. The answer lies apparently not in the increased energy costs of exaggerated begging—such energy costs are small relative to the potential gain in calories—but rather in the damage that any successful cheater would do to its siblings, which share genes with one another. An individual's success in propagating his or her genes can be affected by more than just his or her own personal reproductive success. Because close relatives have many of the same genes, animals that harm their close relatives may in effect be destroying some of their own genes. Therefore, a begging nestling that secures food at the expense of its siblings might actually leave behind fewer copies of its genes overall than it might otherwise.
11. In paragraph 6, the author compares the energy costs of vigorous begging with the potential gain in calories from such begging in order to
○ explain why begging for food vigorously can lead to faster growth and increased size
○ explain how begging vigorously can increase an individual’s chance of propagating its own genes
○ point out a weakness in a possible explanation for why nestlings do not always beg vigorously
○ argue that the benefits of vigorous begging outweigh any possible disadvantages
12. According to paragraph 6, which of the following explains the fact that a well-fed nestling does not beg loudly for more food?
○There is no benefit for a nestling to get more food than it needs to survive.
○By begging loudly for food it does not need, a nestling would unnecessarily expose itself to danger from predators.
○If a nestling begs loudly when it is not truly hungry, then when it is truly hungry its own begging may be drowned out by that of its well-fed siblings.
○More of a nestling's genes will be passed to the next generation if its hungry siblings get enough food to survive.
Paragraph 1: Many signals that animals make seem to impose on the signalers costs that are overly damaging. ■A classic example is noisy begging by nestling songbirds when a parent returns to the nest with food. ■These loud cheeps and peeps might give the location of the nest away to a listening hawk or raccoon, resulting in the death of the defenseless nestlings. ■In fact, when tapes of begging tree swallows were played at an artificial swallow nest containing an egg, the egg in that “noisy” nest was taken or destroyed by predators before the egg in a nearby quiet nest in 29 of 37 trials. ■
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
The cheeping provides important information to the parent, but it could also attract the attention of others.
Where would the sentence best fit?
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Experiments have shed much light on the begging behaviors of baby songbirds.
●
●
●
Answer Choices
○ Songbird species that are especially vulnerable to predators have evolved ways of reducing the dangers associated with begging calls.
○ Songbird parents focus their feeding effort on the nestlings that beg loudest for food.
○ It is genetically disadvantageous for nestlings to behave as if they are really hungry when they are not really hungry.
○ The begging calls of songbird nestlings provide a good example of overly damaging cost to signalers of signaling.
○ The success with which songbird nestlings communicate their hunger to their parents is dependent on the frequencies of the nestlings' begging calls.
○ Songbird nestlings have evolved several different ways to communicate the intensity of their hunger to their parents.
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參考答案：
1. ○3
2. ○1
3. ○2
4. ○2
5. ○3
6. ○4
7. ○2
8.○2
9. ○3
10. ○1
11. ○3
12. ○4
13. ○2
14. Songbird species that…
Songbird parents focus Itisgenetically…
雛鳥(niǎo)的乞食行為
有些動(dòng)物發(fā)出的信號(hào)可能會(huì)給他們自身帶來(lái)極大危害。一個(gè)典型的例子就是歌鳥(niǎo)的雛鳥(niǎo)在它們的父母帶著食物歸巢時(shí)吵鬧的乞食行為。這些喧鬧的叫聲可能會(huì)讓巢外的老鷹和浣熊聽(tīng)到并獲取到它們的位置信息，從而致使毫無(wú)抵抗能力的雛鳥(niǎo)喪命。事實(shí)上，如果在一個(gè)盛有鳥(niǎo)蛋的人工燕窩旁播放樹(shù)燕討食的錄音，這個(gè)試驗(yàn)做了37次，有29次的結(jié)果都是，這個(gè)“嘈雜”鳥(niǎo)巢里的樹(shù)燕蛋比周?chē)察o的鳥(niǎo)巢里的樹(shù)燕蛋更早被捕食者掠走或破壞。
一項(xiàng)關(guān)于地面筑巢的黃鶯與住在相對(duì)安全的樹(shù)上的黃鶯對(duì)比的研究進(jìn)一步為乞食行為的代價(jià)提供了證據(jù)。地面筑巢的黃鶯雛鳥(niǎo)發(fā)出乞食叫聲的頻率要高于樹(shù)上筑巢的黃鶯。這種高頻的聲音不會(huì)傳播的很遠(yuǎn)，可以更好地隱藏在地面鳥(niǎo)巢里單獨(dú)發(fā)出這種聲音而容易成為捕食者攻擊的雛鳥(niǎo)。David Haskell 制做了一些裝有泥制鳥(niǎo)蛋的‘假巢”并放在錄音機(jī)旁的地面上，播放著地面筑巢或樹(shù)上筑巢的黃鶯的乞食聲音。置于樹(shù)上筑巢的聲音旁邊的“被注意的”鳥(niǎo)蛋被發(fā)現(xiàn)的幾率顯然要比地面筑巢的黃鶯的鳥(niǎo)蛋高得多。
一個(gè)關(guān)于乞食行為的假說(shuō)認(rèn)為，乞食聲已經(jīng)進(jìn)化出一種避免引起捕食者注意并及時(shí)作出預(yù)警的特性：比起那些較少受到捕食者捕食的雛鳥(niǎo)相比，被捕食率高的鳥(niǎo)類(lèi)的雛鳥(niǎo)需要發(fā)出更輕柔頻率更好的叫聲。對(duì)亞利桑那森林里的24個(gè)物種的調(diào)查所收集的數(shù)據(jù)證實(shí)了這一假說(shuō)，更多的證據(jù)也表明捕食者的存在迫使乞食聲變得難以察覺(jué)和難以定位。
既然捕食者可以讓雛鳥(niǎo)為食物付出巨大代價(jià)，那么乞食的雛鳥(niǎo)們到底可以從這種交流方式中得到什么益處？可能原因之一是吸引注意力的雛鳥(niǎo)可以準(zhǔn)確傳達(dá)它們很餓而且很健康的信號(hào)，它們這么做是為了讓父母在同一鳥(niǎo)巢的眾多雛鳥(niǎo)中將食物喂給自己。如果這一假說(shuō)成立，那么我們可以斷定雛鳥(niǎo)會(huì)根據(jù)其他爭(zhēng)相引起父母注意的同伴所發(fā)出的信號(hào)來(lái)調(diào)整它們信號(hào)的強(qiáng)度。人們做了一個(gè)實(shí)驗(yàn)，將饑餓的知更鳥(niǎo)雛鳥(niǎo)放進(jìn)那些正常喂養(yǎng)的同類(lèi)的巢中，饑餓的雛鳥(niǎo)會(huì)發(fā)出比平時(shí)更響亮的乞食聲，而其他喂養(yǎng)的很好的雛鳥(niǎo)們也是如此，盡管沒(méi)有饑餓的雛鳥(niǎo)們叫的響。
如果鳥(niǎo)父母是根據(jù)乞食聲音的響亮程度來(lái)給那些健康且更積極乞食的幼鳥(niǎo)喂食，那么鳥(niǎo)父母應(yīng)該是根據(jù)幼崽乞食聲來(lái)分配食物的。所以，如果你將樹(shù)燕雛鳥(niǎo)帶離鳥(niǎo)巢一個(gè)小時(shí)，并將一半雛鳥(niǎo)喂飽同時(shí)不讓另外一半吃東西，當(dāng)把雛鳥(niǎo)們放回巢時(shí)，饑餓的雛鳥(niǎo)們會(huì)比已經(jīng)吃飽的雛鳥(niǎo)們叫得更響，而鳥(niǎo)父母會(huì)給積極乞食的雛鳥(niǎo)們比不積極的雛鳥(niǎo)喂更多的食物。
這些實(shí)驗(yàn)表明，乞食行為很明顯為鳥(niǎo)父母提供了一個(gè)判斷誰(shuí)能吃的最多的需求信號(hào)。但是問(wèn)題又出現(xiàn)了，為什么雛鳥(niǎo)不在它們不餓的時(shí)候大聲乞食呢？如果它們這么做，就可以保證更多的食物，也就能更快的成長(zhǎng)或者擁有更壯的身體，怎么說(shuō)都是有利的。這個(gè)問(wèn)題的答案顯然不是因?yàn)檫^(guò)分乞食會(huì)消耗更多的能量——損耗的能量相比于其潛在能得到的熱量來(lái)說(shuō)只是很小部分——而是因?yàn)槿魏芜@么做成功騙取食物的雛鳥(niǎo)會(huì)帶來(lái)跟它們擁有相同基因的同伴們?cè)斐晌：Α?/span>
一個(gè)物種成功延續(xù)它的基因所產(chǎn)生的影響要比它自身繁殖所帶來(lái)的影響大的多。因?yàn)榻H中有很多相似基因，動(dòng)物傷害它們的近親的同時(shí)很可能會(huì)摧毀一些它們特有的基因。因此，一個(gè)乞食的雛鳥(niǎo)如果以犧牲它的同類(lèi)為代價(jià)來(lái)獲取食物，事實(shí)上可能它能保存下來(lái)的基因要遠(yuǎn)遠(yuǎn)少于相反的做法。
鳥(niǎo)類(lèi)在孵化和育雛期間，相對(duì)于幼體雙親，被稱(chēng)為“親鳥(niǎo)”。
