科学家们早就知道，鸟类在不同的环境下的鸣叫是不同的，而市区的鸟是以更高的音调鸣叫。
Scientists have long known that bird songs vary in different settings and that urban songbirds in particular sing at a higher pitch.
这些问题的答案至今还是未知之数，但是科学家们希望通过声音重放实验测试雌性划蝽是喜欢嘹亮的鸣叫还是温柔的鸣叫。
That's unclear so far, but the scientists are hoping to conduct playback experiments to test female preference for loud over soft calls.
旧金山要塞区麻雀的鸣叫声实际上比它们以往任何时候的叫声都要更高——这样人们才能在驶过附近金门大桥的汽车隆隆声中听到它们的鸣叫。
Sparrows living in San Francisco's Presidio district actually tweet their tunes in a higher register than they did in the past, to be heard over the rumble of cars on the nearby Golden Gate Bridge.
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