救我救我救我啊~~~做过tpo11阅读关于songbird的那道题的请进请进哈~~

zhima427

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—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.

Experiments have shed much light on the begging behaviors of baby songbirds.

songbirds.
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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.

答案是前三个，不明白第四个为什么不是，而且第三在原文只不过是一个可能的解释，答案都说成是陈述句了，这样不是不正确吗？？

zhangxiao91z

个人认为，第三个选项对应的是这句话，应该比较清楚了...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
至于4为什么不对，4对应的是第一段中的Many signals that animals make seem to impose on the signalers costs that are overly damaging. 我也不知道它为什么不对= =但是1,2,3选项很好的对应了全文的各个部分...我是这么想的...

zhima427

个人认为，第三个选项对应的是这句话，应该比较清楚了...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
至于4为什么不对，4对应的是第一段中的Many signals that animals make seem to impose on the signalers costs that are overly damaging. 我也不知道它为什么不对= =但是1,2,3选项很好的对应了全文的各个部分...我是这么想的...

-- by 会员 zhangxiao91z (2012/8/12 18:34:47)

哦，谢谢啊~~但是我问错了，应该是第二个我不认同是正确答案，因为原文说是可能的答案，而答案都变成肯定句了，第三是毫无疑问的~~~第四我都找到原文了，还是首句，难道这个还只是细节吗？不懂不懂~~~