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  3. You Call It Music, They Call It an Air Raid Songs can have a powerful effect on people. Play " Gypsies, Tramps and Thieves"

You Call It Music, They Call It an Air Raid Songs can have a powerful effect on people. Play " Gypsies, Tramps and Thieves"

admin2013-07-11  41
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.
When a black-capped chickadee sings its song______.
选项 A、some predator’s habitat must have been nearby
B、all of its flock mates arrive to drive the enemy out
C、the song carries exact information about threat of the predator
D、the song warns other species to stay out of the territory
答案C
解析 本题考查多处细节。由第二段的前三句话可知：山雀的歌声是个暗号，根据捕食动物的大小、危险程度的不同而变化，是目前发现的最精确的报警呼叫系统，因此[C]项正确。由第一段末句可知，[A]项错在habitat，捕食动物在附近并不意味着它的巢穴也在附近。由第三段第三句可知，当听到呼叫，其他的鸟要么冲上来掩护，要么保持不动以免被发现。因此[B]项不正确。鸟儿的歌曲只对同类有警示作用，因此[D]项不正确。
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