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You Call It Music, They Call It an Air Raid Songs can ha

游客2024-12-16  16
问题                     You Call It Music, They Call It an Air Raid
    Songs can have a powerful effect on people. Play " Gypsies, Tramps and Thieves" to many baby boomers, for example, and chances are they’ll run off, hands over their ears. Songs can have a powerful effect among birds, too. Consider the black-capped chickadee. When it sings its " chick-a-dee" song, its flock mates come running. The song is a warning that a hawk, owl or other predator is moving nearby, and the other chickadees arrive to harass the enemy until it leaves.
    Researchers from the University of Montana have discovered that this warning call is a coded signal. By varying the call, a bird communicates to other birds the size of the predator, and thus the scope of the danger. " This is so far the most finely detailed alarm call system that we’ve found," said the lead researcher, Christopher N. Templeton, who is now a doctoral student at the University of Washington. The findings appear in the current issue of the journal Science.
    Mr.Templeton and his colleagues exposed chickadees to 15 different species of predators and recorded and analyzed the calls the birds made. In addition to "chick-a-dee", the birds make a high-pitched "sect" call when they spy a predator flying in the air. Upon hearing this call, the other birds either dive for cover or remain motionless so as not to be spotted. But it’s the "chick-a-dee" call that the researchers focused on. "They change a number of different features about these calls," Mr. Templeton said. "But most are not audible to us except the number of dees’ at the end."
They found that the birds varied the number of "dee" sounds depending on the size of the predator. More "dees"—as many as 21 in one case—were sounded for smaller predators like the Northern pygmy owl. Because chickadees are small and fast, smaller, more quick-moving predators are more of a threat than larger ones.
    The more "dees", the more chickadees show up to harass the predator, by dive-bombing it or making noises in its face. "The goal is to drive it out of their territory so that it is no longer a threat," Mr. Templeton said. This "mobbing" response to the calls is probably learned behavior, he said, a way that birds teach their young about risks. "It’s a means by which adults tell the kids in the flock, ’ These guys are dangerous,’" Mr. Templeton said. [br] Which of the following is Not an example of "coded signal" (Line 3, Para. 2)?
选项 A、Bees perform dances to convey that the food source is not far away from the hive.
B、Parrots imitate human speech and whistle when kept in captivity.
C、Huntsmen use horns to indicate the presence of a fox in a field or to call the hunting party together.
D、Bats and dolphins use high frequency sounds for communication and navigation.
答案 B
解析 本题考查对文中内容的理解和演绎推理。coded signal出现在第二段首句，根据上下文鸟儿的例子可知，它指的是一种用来交流或预警的信号，信号内容应是隐藏的，信号方式一般是约定俗成的，不易被其他种类的动物听懂。依次类推，只有[B]项说明的是动物的模仿能力，不属于暗号。
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