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  3. To the people of Europe, cuckoos are harbingers of spring. To European birds, though, the cuckoo’s call is less welcome—for cuck

To the people of Europe, cuckoos are harbingers of spring. To European birds, though, the cuckoo’s call is less welcome—for cuck

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问题     To the people of Europe, cuckoos are harbingers of spring. To European birds, though, the cuckoo’s call is less welcome—for cuckoos, notoriously, are parasites of others’ nests. They lay their eggs in them and leave the hapless foster-parents to do the hard work of bringing up baby.
    But are those parents always so hapless? How the cuckoo gets away with it has been the subject of much speculation, and some biologists think that, at least some of the time, cuckoos may bring subtle benefits which help offset the undoubted costs they impose. And, as a paper just published in Science outlines, for one sort of cuckoo and one sort of surrogate parent, that does appear to be the case.
    Daniela Canestrari of Oviedo University, in Spain, and her colleagues looked at relations between great spotted cuckoos and carrion crows. Unlike some nest parasites, great spotted cuckoos do not evict the eggs or young of their hosts. They do, however, compete with them for food. The result is that crows which raise both their own and young cuckoos to the point when they can fly fledge fewer of their own chicks than do crows which fledge a clutch without cuckoos. This suggests, as might be expected, that cuckoos are a bad thing.
    Dr. Canestrari, however, decided to look a little deeper. She suspected that though their fledged clutches were smaller, crows with cuckoos in the nest were more likely to fledge at least some young than were unparasitised crows. That might be enough to compensate for the lower number of fledgling per nest.
    Her idea was that cuckoo nestlings engage in a form of chemical warfare with predators. They certainly secrete a noxious mixture of chemicals. This suggests these chemicals have a specific purpose, rather than being mere waste products. And when she offered meat with cuckoo nestling secretion to wild cats and birds of prey, which are predators of crow nests in the study area, they would not touch it. That indicates having a cuckoo or two in the nest really is a defence.
    To prove the point, she did some experiments—swapping cuckoo nestlings from the nests where they had hatched into other nests without cuckoos. The receiving nests turned out to be more likely to yield at least some fledgling crows than did other nests that had never had cuckoos in them. Moreover, 16 years’ worth of observations of nests suggested that, though the difference was small, having cuckoo chicks in the nest was actually a better strategy on average than not having them.
To other birds, cuckoos have a bad name because______.
选项 A、they eat other birds’ babies
B、they get paid without work
C、they expel other birds’ chicks
D、they lay eggs in their own nests
答案B
解析 根据题干中的to other birds，cuckoos等词定位到第一段。再根据have a bad name“声名狼藉”定位到第二行cuckoo’s call is less welcome一句，答案来自破折号之后：forcuckoos，notoriously，are parasites of others’nests．They lay their eggs in them and leave thehapless foster—parents to do the hard work of bringing up baby．大意为“因为杜鹃臭名昭著，它们是其他鸟类巢穴的寄生物。它们把蛋下在别的鸟巢里，让倒霉的养父母们辛苦抚育孩子。”选项[A]they eat other birds’babies“它们吃掉其他幼鸟”，[C]they expel other birds’chicks“它们驱逐其他幼鸟”和[D]they lay eggs in their own nests“它们将蛋下在自己巢穴里”与文章大意不符，答案为[B]they get paid without work“它们不劳而获”。
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